chemical composition of dietary fiber and polyphenols of wine
TRANSCRIPT
AN ABSTRACT OF THE THESIS OF
Qian Deng for the degree of Master of Science in Food Science and Technology
presented on February 11, 2011.
Title: Chemical Composition of Dietary Fiber and Polyphenols of Wine Grape
Pomace Skins and Development of Wine Grape (cv. Merlot) Pomace Extract Based
Films.
Abstract approved:
_____________________________________________________________________
Yanyun Zhao
The objectives of this project were to investigate the chemical composition of
five varieties of wine grape pomace (WGP) skins obtained in the Pacific Northwest of
the United States with the emphasis on dietary fiber (DF) and polyphenolic
compounds, and further to evaluate the feasibility of developing WGP extract based
edible films in terms of their physicochemical, nutritional and antimicrobial properties.
Research studied two varieties of white WGP (WWGP) skins (vinifera L. cv. Morio
Muscat and cv. Muller Thurgau) and three varieties of red WGP (RWGP) skins (Vitis
vinifera L. cv. Cabernet Sauvignon, cv. Pinot Noir and cv. Merlot). DF was measured
by gravimetric-enzymatic method with sugar profiling by HPLC-ELSD. Soluble
polyphenols were extracted by 70% acetone/0.1% HCl/29.9% deionized water and
measured spectrophotometrically.
The major composition of insoluble DF (IDF) were Klason lignin (7.9-36.1%
DM), neutral sugars (4.9-14.6% DM), and uronic acid (3.6-8.5% DM), which weighed
more than 95.1% of total DF in all five WGP varieties. RWGP was significantly
higher in DF (51.1-56.3% DM) than those of WWGP (17.3-28.0% DM), but lower in
soluble sugar (1.3-1.7% DM in RWGP vs. 55.8-77.5% DM in WWGP) (p<0.05).
RWGP contained larger amount of soluble pectin (water soluble, chelator soluble and
hydroxide soluble) (5.1-5.6% DM) compared with that of WWGP (3.2-4.1% DM).
Compared with WWGP, RWGP had higher values in total phenolics content (21.4-
26.7 mg GAE/g DM in RWGP vs. 11.6-15.8 mg GAE/g DM in WWGP) and DPPH
radical scavenging activity (32.2-40.2 mg AAE/g DM in RWGP vs. 20.5-25.6 mg
AAE/g DM in WWGP) (p<0.05). The total flavanol and proanthocyanidin contents
were ranged from 31.0 to 61.2 mg CE/g DM and 8.0 to 24.1 mg/g DM, respectively
for the five WGP varieties. This study not only demonstrated that the skins of WGP
can be ideal sources of DF rich in bioactive compounds, but also built up the baseline
data for developing innovative utilizations of both red and white wine grape pomace
skins.
Because of its highest amounts of water soluble pectin (4.5 mg GUAE/g DM)
and total phenolic content (25.0 mg GAE/g DM) among five WGP varieties, RWGP
(cv. Merlot) was selected to develop WGP extract based films accompanying the study
on their physicochemical, nutritional and antibacterial properties. Pomace extract (PE)
was obtained by hot water extraction and had a total soluble solid of 3.6% and pH 3.65.
Plant based polysaccharides, low methxyl pectin (LMP, 0.75% w/w), sodium alginate
(SA, 0.3% w/w), or Ticafilm® (TF, 2% w/w), was added into PE for film formation,
respectively. Elongation at break and tensile strength of the films were 23% and 4.04
MPa for TF-PE film, 25% and 1.12 MPa for SA-PE film, and 9.89% and 1.56 MPa for
LMP-PE film. Water vapor permeability of LMP-PE and SA-PE films was 63 and 60
g mm m-2
d-1
kPa, respectively, lower than that of TF-PE film (70 g mm m-2
d-1
kPa)
(p<0.05). LMP-PE film had higher water solubility, indicated by the haze percentage
of water after 24 h of film immersion (52.8%) than that of TF-PE (25.7%) and SA-PE
(15.9%) films, and also released the highest amount of phenolics (96.6%) than that of
TF-PE (93.8%) and SA-PE (80.5%) films. PE films showed antibacterial activity
against both Escherichia coli and Listeria innocua, in which approximate 5 log
reductions in E. coli and 1.7-3.0 log reductions in L. innocua were observed at the end
of 24 h incubation test compared with the control. In conclusion, wine grape pomace
extract based edible films with the addition of a small amount of commercial
polysaccharides showed attractive color and comparable mechanical and water barrier
properties to other edible films. The films also demonstrated their antioxidant and
antimicrobial functions.
The results from this study provided guidance on the utilizations of WGP skins
based on their chemical compositions, and also demonstrate the possibility of
developing innovative packaging materials using WGP skins extracts that may be used
as colorful wraps or coatings for food, pharmaceutical or other similar applications.
©Copyright by Qian Deng
February 11, 2011
All Rights Reserved
Chemical Composition of Dietary Fiber and Polyphenols of Wine Grape Pomace
Skins and Development of Wine Grape (cv. Merlot) Pomace Extract Based Films
by
Qian Deng
A THESIS
submitted to
Oregon State University
In partial fulfillment of
the requirements for the
degree of
Master of Science
Presented February 11, 2011
Commencement June 2011
Master of Science thesis of Qian Deng presented on February 11, 2011.
APPROVED:
_____________________________________________________________________
Major professor, representing Food Science and Technology
_____________________________________________________________________
Head of the Department of Food Science and Technology
_____________________________________________________________________
Dean of the Graduate School
I understand that my thesis will become part of the permanent collection of Oregon
State University libraries. My Signature below authorizes release of my thesis to any
reader upon request.
_____________________________________________________________________
Qian Deng, Author
ACKNOWLEDGEMENTS
This research could not be successfully carried out without the supports from
people around me. I feel greatly thankful for being in the Department of Food Science
& Technology at Oregon State University. I sincerely acknowledge to those who have
helped me in this two and half years.
I would like to dedicate my sincere thanks to my major adviser Dr. Yanyun
Zhao for advising me throughout my whole master program with constantly
encouragement. Without her patient guidance, it is impossible for me to accomplish in
the master program. I learned academic knowledge, laboratorial skills, and
interpersonal skills from her, which in future will benefit me for lifelong time.
I would like to recognize Dr. Michael Penner for his professional guidance on
dietary fiber and chemical composition analysis, letting me to use his equipments, and
being my committee member. Many thanks to Dr. Mark Daeschel for providing me
with wine grape pomace, allowing me to use his lab equipments, and also being my
committee member. I appreciate Dr. Gita Cherian being my graduate council
representative and participating in my master program.
I would like to thank Dr. James Osborne for donating wine grape pomace, Dr.
Jingyun Duan for teaching me to run microbial test and giving me lots of help in
addition of research, Dr. Seth Cohen for generously donating purified wine grape
condensed tannins, and Mr. Jeff Goby for helping me profile neutral sugar by HPLC-
ELSD. What’s more, I dedicate many thanks to Mr. Jeff Clawson for his time and
effort to help me overcome many instrument issues, Ms. Supaporn
Sophonputtanaphoca for giving me lots of advice on determining dietary fiber, and Ms.
Jooyeoun Jung for determining resistant proteins for me.
Many thanks also go to Dr. Robert McGorrin, and main office ladies, Linda
Hoyser, Linda Dunn, Christina Hull, Debby Iola, and Debby Yacas for providing
assistance in every aspect, and my awesome friends in Corvallis who make my life
more than just research and give me physical and mental supports continuously.
Last but not the least, I deeply acknowledge my family in China and relatives
in the United States for unconditionally supporting me to come here and pursue my
M.S. in Food Science and Technology at Oregon State University. Their love always
comforts me whenever I am frustrated, makes me strong whenever I am weak, and
encourages me to fulfill my goal.
CONTRIBUTION OF AUTHORS
Dr. Yanyun Zhao assisted with the experimental design, data analysis, and
writing of each chapter. Dr. Michael H Penner was involved with writing of Chapter 3.
TABLE OF CONTENTS
Page
1 CHAPTER 1 Introduction....................................................................... 1
2 CHAPTER 2 Literature Review.............................................................. 5
2.1 Overview of dietary fiber...................................................................
5
2.1.1 Definition of dietary fiber...........................................................
2.1.1.1 Non-digestible carbohydrates............................................
2.1.1.2 Lignin.................................................................................
2.1.1.3 Associated plant substances...............................................
2.1.2 Health benefits of dietary fiber....................................................
2.1.3 Analysis of dietary fiber..............................................................
5
5
8
8
9
10
2.2 Overview of wine grape pomace.......................................................
12
2.2.1 Wine grape production and varieties in the Pacific
Northwest of the United States.....................................................
2.2.2 Wine making procedure...............................................................
2.2.2.1 Red wine process.................................................................
2.2.2.2 White wine process……......................................................
2.2.3 Wine grape pomace......................................................................
2.2.4 Antioxidant activity of WGP........................................................
2.2.5 Antimicrobial activity of WGP....................................................
2.2.6 Extraction of phenolic compounds from WGP............................
2.2.7 Utilizations of WGP.....................................................................
12
14
15
16
16
18
18
19
20
2.3 Edible films and coatings...................................................................
23
2.3.1 History of edible films and coating..............................................
2.3.2 Functions of edible films and coatings for food
applications...................................................................................
2.3.3 Film forming materials..................................................................
2.3.4 Overview of edible films and coatings originated
from plant materials.......................................................................
2.3.4.1 Sources of plants...................................................................
2.3.4.2 Antimicrobial property of edible films and coatings
originated from plant materials.............................................
2.3.4.3 Antioxidant property of edible films and coatings
originated from plant materials.............................................
2.3.4.4 Applications of edible films and coatings originated
from plant materials in foods.................................................
23
23
25
26
26
28
29
29
TABLE OF CONTENTS (Continued)
Page
2.4 Conclusion............................................................................................ 30
2.5 Reference.............................................................................................
31
3 CHAPTER 3 Dietary Fiber and Polyphenols of Five Different
Varieties of Wine Grape Pomace Skins....................................................
43
Abstract.....................................................................................................
44
Introduction..............................................................................................
45
Materials and Methods..............................................................................
46
Results and Discussion...............................................................................
53
Conclusion.................................................................................................
68
Acknowledge............................................................................................
68
Reference..................................................................................................
69
4 CHAPTER 4 Physicochemical, Nutritional and Antimicrobial
Properties of Wine Grape (cv. Merlot) Pomace Extract Based Films.......
74
Abstract.....................................................................................................
75
Introduction...............................................................................................
76
Materials and Methods..............................................................................
78
Results and Discussion...............................................................................
84
Conclusion..................................................................................................
101
Reference....................................................................................................
101
5 CHAPTER 5 General Conclusion.............................................................. 106
BIBLIOGRAPHY........................................................................................... 108
TABLE OF CONTENTS (Continued)
Page
APPENDIX Chromatograms and correction factors of neutral sugars.......... 126
LIST OF FIGURES
Figure Page
3.1 Fractionation of soluble pectin (water soluble, chelator soluble and
hydroxide soluble pectin) from wine grape pomace (WGP) expressed as mg
GUAE/g DM.................................................................................................
56
3.2 Correlation between RSA and TPC (R=0.989), RSA and TFC (R=0.653),
and RSA and PAC (R=0.667) for five WGP varieties.................................
66
4.1 Surface microstructures of wine grape pomace extract based films
viewed at magnification 40×; (a) TF-PE; (b) LMP-PE; (c) SA-PE. LMP=low
methoxyl pectin.............................................................................................
87
4.2 Water vapor permeability (g mm m-2
d-1
kPa-1
) of wine grape pomace
extract based films corresponding to film thickness (μm).............................
93
4.3 Solubility of wine grape pomace extract based films in
aqueous solution..............................................................................................
95
4.4 Total phenolics content (TPC) in film forming solutions (FFS)
and amount of TPC released from films at the end of 24 h water
immersion test.................................................................................................
96
4.5 TPC releasing characterization of wine grape pomace extract based films
in distilled water corresponding to time at room temperature..........................
97
4.6 The inhibiting activity of wine grape pomace extract based films against
E. coli and L. innocua corresponding to time at room temperature..................
100
LIST OF TABLES
Table Page
2.1 Common sources of non-digestible carbohydrates (NDC) from
references......................................................................................................
7
2.2 Official methods for analyzing dietary fiber from food
stuffs.............................................................................................................
11
2.3 Summary of 2008 and 2009 wine grape production and average
prices in Oregon and Washington.................................................................
13
2.4 Treatment and usage of grape wastes, physicochemical properties
and their utilization........................................................................................
21
3.1 Crude protein, fat and ash content of five varieties of wine grape
pomace (WGP) .............................................................................................
54
3.2 The major carbohydrate fractions of wine grape pomace (WGP)...........
55
3.3 Dietary fiber content in five different wine grape pomace (WGP).........
59
3.4 Bound condensed tannins (CT) and resistant protein (RP) of insoluble
dietary fiber (IDF) residue (% DM)................................................................
61
3.5 Soluble phenolic compounds of different varieties of wine grape pomace
(WGP) extracted by method A and B.............................................................
64
3.6 The documentary values of total phenolic compounds from wine grape
pomace (WGP), fresh wine grape berry, and other fruit byproducts............
65
4.1 Formulations of wine grape pomace (WGP) extract based film forming
solutions (FFS).................................................................................................
79
4.2 Total soluble solids (TSS), pH and casting weight of film forming
solutions (FFS).................................................................................................
85
4.3 Moisture content, water activity, density, mechanical properties and
color of wine grape pomace extract based films...........................................
88
LIST OF TABLES (Continued)
Table Page
4.4 Bibliographical values of mechanical properties and water barrier
properties of fruit pomace base edible films.................................................
91
Chemical Composition of Dietary Fiber and Polyphenols of Wine Grape Pomace
Skins and Development of Wine Grape (cv. Merlot) Pomace Extract Based Films
CHAPTER 1
Introduction
Wine grape pomace (WGP), the byproduct of winery industry, is composed of
wine grape skins, seeds, and stems. WGP is a rich source of malate, ethanol, tartrate,
citric acid, grape seed oil and dietary fiber (DF) (Arvanitoyannis, et al., 2006).
Additionally, due to the pronouncing amount of polyphenols (Katalinić et al., 2000),
WGP are reported to be high in bioactive compounds with anticancer, antioxidant,
anti-inflammatory, and antimicrobial properties (Pinelo et al., 2006; Arvanitoyannis, et
al., 2006; Spigno and De Faveri, 2007; Cowan, 1999; Özkan, et al., 2004). The Pacific
Northwest region of the United States are the leading wine grape production states in
the country, in which Washington produced 156,000 tons in 2009 and Oregon 40,200
tons in 2009 (USDA-NASS, 2010a,b). The increasing yield of WGP in US Pacific
Northwest and their recognized health benefits drove more studies on their chemical
compositions for developing value-added applications.
DF, defined as “edible parts of plants or analogous carbohydrates that are
resistant to digestion and absorption in the human small intestine with complete or
partial fermentation in the large intestine” (AACC, 2001), is originated from plant cell
walls and is revealed to be of great health benefits (Dreher, 2001). WGP of European
varieties (cv. Airén, Cencibel, Mango Negro, Prensal Blanc) was reported to be high
in insoluble dietary fiber (IDF), condensed tannins, but low in soluble dietary fiber
(SDF) (Valiente et al., 1995; Bravo and Saura-Colixto, 1998; Llobera and Cañellas,
2007; Llobera and Cañellas, 2008; Goni et al., 2009). However, little is known about
the WGP of US varieties. Therefore, one of the objectives of this study was to
characterize DF in two varieties of white WGP (WWGP) (cv. Muller Thurgau, Morio
2
Muscat) and three varieties of red WGP (RWGP) (cv. Merlot, Pinot Noir, Cabernet
Sauvignon) grown in the Pacific Northwest region. Studies on WGP have emphasized
on optimizing the recovery of polyphenols from WGP by investigating extraction
conditions (Pinelo et al., 2006a). However, it has not come up a universal protocol to
extract polyphenolic compounds from WGP which is able to enhance the extraction
efficiency, reduce the solvent usage as well as improve the extract purity. Therefore, it
is necessary to optimize extraction methods based on previous publications. Because
WGP skins weigh 82% of fresh WGP (Jiang et al., 2011) and contain 39 types of
polyphenols (Kammerer et al., 2004), this study aimed at characterizing DF,
investigating the method of extracting polyphenolic compounds, and determining
polyphenolic compounds in WGP skins originated from Pacific Northwest of the
United States.
On the other hand, motivated by the increasing demands on environmentally
friendly packaging materials, there are more development of edible films and coatings
with competitive mechanical and mass barriers (i.e. gas, moisture, flavor, lipid, aroma)
properties to traditional plastic wraps (Han and Gennadios, 2005). Plant materials have
been used to form edible films and coatings because they not only consist of required
film forming materials (i.e. starch, pectin, soluble sugar, moisture, fatty acid, wax) but
also some bioactive compounds, such as polyphenos and organic acids. Park and Zhao
(2006) successfully developed cranberry pomace extract based edible films with the
aid of pectin and plasticizers. WGP skins contain a various amounts of
polysaccharides and sugars, as well as bioactive compounds, which led to the
hypothesis that WGP extracts can be used to develop innovative edible films with
additional nutritional and antimicrobial functions. Based on our best knowledge, no
study has investigated nutritional and antimicrobial properties of WGP extracts based
edible films. Therefore, the objective of this study was to develop WGP extracts based
films by not only investigating their physiochemical properties, but also the nutritional
and antimicrobial properties.
3
Overall, the objectives of this project consisted of two parts. First, the DF and
polyphenols of five varieties of WGP skins in the Pacific Northwest region of the
United States were studied in order to provide some baseline data for developing
further applications of WGP skins. Secondly, WGP (cv. Merlot) extract based edible
films were developed and evaluated in terms of their physicochemical, nutritional, and
antimicrobial properties.
Literature cited
American association of cereal chemists (AACC), 2001. The definition of dietary fiber.
46, 112-126.
Arvanitoyannins, I.S., Ladas, D., Mavromatic, A, 2006. Potential uses and
applications of treated wine waste: a review. Int. J. Food Sci. Tech. 41, 475-587.
Bravo, L., Saura-Calixto, F., 1998. Characterization of dietary fiber and the In Vitro
indigestible fraction of grape pomace. Am. J. Enol. Vitic. 49, 135-141.
Cowan, M.M., 1999. Plant products as antimicrobial agents. Clin. Microbiol. Rev. 12,
564-582.
Dreher, M.L., 2001. Dietary fiber overview. In Cho, S.S. and Dreher, M.L. (Eds.),
Handbook of dietary fiber. Marcel Dekker, Inc., New York, USA. pp1-194.
Goñi, I., Díaz-Rubio, M.E., Pérez-Jimenez, J., Saura-Calixto, F., 2009. Towards and
updated methodology for measurement of dietary fiber, including associated
polyphenols, in food and beverages. Food Res. Int. 42, 840-846.
Han, J. H., Gennadios, A., 2005. Edible films and coatings: a review. In Han, J. H.
(Ed.), Innovations in food packaging. Elsevier academic press, Oxford, UK, pp 237-
262.
Jiang, Y., Simonsen, J., Zhao, Y., 2011. Compression-molded biocomposite boards
from red and white wine grape pomaces. J. Appl. Polym. Sci. 119, 2834-2846.
Kammerer, D., Claus, A., Carles, R., Schieber, A., 2004. Polyphenol screening of
pomace from red and white grape varieties (Vitis Vinefera L.) by HPLC-DAD-
MS/MS.J, Agric. Food Chem. 52, 4360-4367.
Katalinić, V., Moţina, S.S., Skroza, D., Generaliţ, I., Abramović, H., Miloš, M.,
Ljubenkov, I., Piskernik, S., Pezo, I., Terpinc, P., Boban, M., 2010. Polyphenolic
4
profile, antioxidant properties and antimicrobial activity of grape skin extracts of 14
Vitis vinifera varieties grown in Dalmatia (Croatia). Food Chem.. 119, 715-723.
Özkan, G., Sagdiç, O., Baydar N.G., Kurumahmutoglu, Z. 2004. Antibacterial
activities and total phenolic contents of grape pomace extracts. J. Sci. Food Agric. 84,
1807-1811.
Park S., Zhao Y., 2006. Development and characterization of edible films from
cranberry pomace extracts. J. Food Sci. 71, 95-101.
Pinelo, M., Arnous, A., Meyer, A.S., 2006 (a). Upgrading of grape skins: significance
of plant cell-wall structural components and extraction techniques for phenol release.
Trends Food Sci. Tech. 17, 579-590.
Spigno, G., De Faveri, D.M., 2007. Antioxidant from grape stalks and marc: influence
of extraction procedure on yield, purity and antioxidant power of the extract. J. Food
Eng. 78, 793-801.
Valiente, C., Arrigoni, E., Esteban, R.M., Amado, R., 1995. Grape pomace as a
potential food fiber. J. Food Sci. 60, 818-820.
USDA-NASS (United State Department of Agriculture-National Agricultural
Statistics Service), 2010 (a). Grape release (Washington). Revised and reposted
February 9, 2010.
USDA-NASS (United State Department of Agriculture-National Agricultural
Statistics Service), 2010 (b). 2009 Oregon vineyard and winery report. February 2010.
5
CHAPTER 2
Literature Review
2.1 Overview of dietary fiber
2.1.1 Definition of dietary fiber
The term “dietary fiber” (DF) was firstly introduced by Hipsley (1953),
defined as cellulose, hemicellulose, and lignin in food and was then adopted as the
remnant of plant cell walls which resists to the alimentary enzymatic hydrolysis in
human bodies in 1970s (Trowell 1972; Trowell 1978). The definition of DF has
gradually merged from two perspectives: chemical characterizations and physiological
functions. American Association of Cereal Chemists (AACC, 2001) suggested the
definition of DF as “dietary fiber is the edible parts of plants or analogous
carbohydrates that are resistant to digestion and absorption in the human small
intestine with complete or partial fermentation in the large intestine”. The constituents
of DF include non-starch polysaccharides and resistant oligosaccharides, analogous
carbohydrates, lignin, and associated plant substances (AACC, 2001). DF is also
classified into insoluble DF (IDF) and soluble DF (SDF), in which SDF is water
soluble after enzymatic treatments, while the IDF is the insoluble DF after enzymatic
treatments (AACC, 2001).
Antioxidant DF (ADF) was first introduced by Saura-Calixto (1998) who
defined a product with larger than 50% DF and high antioxidant activities (per gram
sample has capacity of inhibiting lipid oxidation ≥ 200 mg vitamin E equivalent by
thiocyanate procedure and free radical scavenging capacity ≥ 50 mg vitamin E by
DPPH method) (Saura-Calixto, 1998). Wine grape pomace (Saura-Calixto, 1998),
guava fruit (Jeménez-Escrig et al., 2001) and the stems and fruits of cactus (Opuntia
ficusindica) (Bensadón et al, 2010) were all identified as the good sources of ADF.
6
2.1.1.1 Non-digestible carbohydrates
As indicated by AACC (2001), the non-digestible carbohydrates (NDC)
include non-starch polysaccharides, resistant oligosaccharides of which the degree of
polymerization are within 3~10, and analogous carbohydrates (“i.e., modified
cellulose, resistant starches, and synthesized polymers”) (AACC, 2001). The NDC has
been characterized from many resources of plant cell walls and some of them are
listed in Table 2.1. Cellulose and hemicellulose are the most abundant NDC in nature
(Das and Singh, 2004). They belong to IDF fraction and usually come with lignin (Das
and Singh, 2004). Additionally, part of NDC is SDF, such as pectin, pectic
polysaccharides and inulin. Pectin or pectic polysaccharides are abundant in plant cell
walls. For commercial applications, apple and citrus fruits are the major raw materials
for the production of pectin (Thibault and Ralet, 2003). Inulin and olifructans have
been promoted as sources of functional foods in the past decade and are mainly
extracted from chicory roots for industrial usage (Niness, 1999). Except for the NDC
discussed in Table 2.1, some other common plant cell wall materials, such as alginates,
carrageenans, and gums are also widely spread in nature.
7
Table 2.1 Common sources of non-digestible carbohydrates (NDC) from references NDC Degree of
polymerization (DP)
Plant sources Solubility in water Structure
Cellulose &
hemicellulose
DP for cellulose varies,
from 30-300) (Isogai et
al., 2008); DP for
hemicellulose is
smaller than cellulose.
Abundant in nature, such as
straws (cellulose 30%-57%
DM; hemicellulose 15%-29%
DM), fruits & vegetables
(cellulose 1%-13.4% DM;
hemicellulose 4%-36%);
cereals (cellulose 2%-12%;
hemicellulose ~ 3%) (Das and
Singh, 2004).
Cellulose and
hemicellulose are
not water soluble;
but the cellulose
derivatives are
water soluble.
Cellulose is a linear polymer of which
the glucose units are linked by β 1, 4
carbon bonds.
Hemicellulose is formed into a shorter
and branched chain and includes other
sugar residues other than glucose, such
as xylose, mannose, galactose,
rhamnose and arabinose.
Pectin Various “ ~35% of primary walls in
dicots and non-graminaceous
monocots, 2-10% of grass and
other commelinoid primary
walls; and up to 5% of walls
in woody tissue” (Mohnen,
2008)
Yes Pectins are mainly composed of 1,4
linked-α-D-galacturonic acids as
backbone units. Homogalacturonan is a
kind of linear structure while
rhamnogalacturonan I and
rhamnogalacturonan II are hairy
structures with the galacturonic acid
backbone and other sugar subunit
branches (Mohnen, 2008).
Polyfructans
(Inulin &
Oligofructans
)
DP for inulin is 2-6;
DP for oligofructans is
2-8 (Roberfroid, 2007).
Presenting in >36,000 plant
species (Carpita et al., 1989);
chicory roots as the major raw
materials for extracting inulin
and oligofructans (Niness,
1999)
Highly soluble They are heterogeneous structures. The
fructose units are linked by β 1, 2
carbon bonds in fructose oligomers,
polymers, sucrose and glucose residues
(Roberfroid, 2007).
8
2.1.1.2 Lignin
“Lignin is a hydrophobic polymer formed through enzyme-mediated radical
coupling of monolignols, mainly coniferyl and sinapyl alcohols” (Hatfield and
Fukushima, 2005). Lignin is indigestible in intestinal tract and comes with cellulose
and hemicellulose in plant cell walls (Hatfield and Fukushima, 2005; Das and Singh,
2004). Generally, lignin takes about 7-13% dry matter (DM) in agricultural residues
(straw, hulls, and bagasse); the amount of lignin in fruits and vegetables ranges widely
from traceable amount to 35% DM depending on the varieties, such as lemon has 35%
DM lignin but potato has only a traceable amount (Das and Singh, 2004).
Although numerous methods have been applied to quantify the lignin in
forages, including acid detergent, Klason, and permanganate methods (Hatfield and
Fukushima, 2005), the determination of lignin for dietary fiber in foods and plant
residue most frequently employs Klason method which is to weigh the residue after
acid hydrolysis of insoluble dietary fiber fraction.
2.1.1.3 Associated plant substances
In the plant tissues, there are associated plant substances attached in the lignin
and the non-starch polysaccharides such as waxes, phytate, cutin, saponins, suberin,
and tannins (AACC, 2001). Those substances have been widely studied and proven to
be of various health benefits to human bodies. For example, tannins, presenting widely
in nature (i.e. legums, wine, and berries) are usually divided into two groups: water
soluble tannins (simple phenolic compounds with low degree of polymerization (DP))
and condensed tannins (a chain of flavonoid units with DP of 2-50). Tannins show
antimicrobial, antioxidant, and anti-radical scavenging activities, and are also
anticarcinogens (Dokkum et al., 2008). In general, although the amount is smaller than
NDC and lignin in plant cell walls, the plant associated substances usually play several
bioactive functions on human bodies, thus have attracted increasing attentions from
researchers.
9
2.1.2 Health benefits of dietary fiber
Health benefits of DF have been widely studied and many of them have been
proven in recent decades. One of the most important health benefits of DF is to
promote the laxation and increase fecal bulks therefore to prevent colon diseases.
Physicochemical properties of DF (soluble or insoluble), gut microflora, and human
gastrointestinal (GI) tract influence the effects of DF towards human health (Stewart et
al., 2010). IDF in cereals, for instant, was revealed to be the effective laxatives
(Topping, 2007), while some SDF, such as pullulan, resistant starch, soluble fiber
dextrin, and soluble corn fiber are also ideal candidates for promoting colon health
(Stewart et al., 2010). On the other hand, high fiber diets showed great influences on
preventing coronary heart disease (Anderson et al., 1994; AACC, 2001; Champ et al.,
2003). The soluble and viscous DF distributing in foods (apples, barleys, beans, fruits,
oatmeals, etc.), for instant, beet fiber, guar gum, pectin, and soy proteins, can
effectively reduce the risk of cardiovascular disease by “changing of diet composition,
reducing cholesterol adsorption, changing of bile acid synthesis and reducing
cholesterol biosynthesis” (Marlett, 2001). Many other health benefits contributed by
DF have also been continuously studied, such as weigh regulation to prevent obesity
(Chandalia et al., 2000; Howarth et al., 2001), breast and prostate cancer (Marlett,
2001).
Food and Nutrition Board of the National Academy of Sciences (2002) has
suggested the dietary fiber intake amounts for different genders during various age
groups. Overall, adult males are suggested to digest more DF than adult females, 30-
38 g/d and 21-26 g/d, respectively. During the times of pregnancy and lactation,
women require a bit higher amount of DF, 28 g/d and 29 g/d, respectively. The
suggested DF for children is lower than adults (19-25 g/d). Because DF from natural
sources also has various plant associated compounds which are able to provide more
health benefits, it is also recommended to intake dietary fiber from natural plant
tissues instead of from nutraceutical supplements.
10
2.1.3 Analysis of dietary fiber
The methods used for analyzing DF vary based on the purposes of the studies.
Generally speaking, food stuffs are tested in powder form and DF from food powders
are separated into two fractions: SDF and IDF. They are then quantified and/or
characterized photometrically, chromatographically, and/or gravimetrically. It is
important to quantify the portion of SDF and IDF in food stuffs, not only for the
purpose of labeling (Champ et al., 2003), but also the solubility of DF associated with
the physiological effects on human health as was mentioned in 2.1.2. American
Official Association of Chemists (AOAC) has approved about 7 official methods of
DF analysis (Table 2.2), most parts of which focus on the enzymatic treatment and
gravimetrical measurement of DF. The enzymatic methods imitate the food digestion
in upper alimentary tracts (Champ et al., 2003) so that the measured DF is able to
better represent the physiological effects on animal bodies. Therefore, enzymatic
methods are usually applied for analyzing DF in foods.
11
Table 2.2 Official methods for analyzing dietary fiber from food stuffs Designation
a Title
a Description
b
AOAC 985.29
(AOAC, 2007)
Total dietary fiber in foods, enzymatic-
gravimetric method
Dried food sample is subsequently treated with α-amylase, protease and
amyloglucosidase. After precipitating by ethanol, the sample is filtrated through a
fritted crucible and then weighed to quantify. This method is only applied in the case
that only the amount of total dietary fiber (TDF) is taken into consideration.
AOAC 991.42
(AOAC, 2007)
Insoluble dietary fiber in foods and food
products, enzymatic-gravimetric method,
phosphate buffer
Dried food sample is treated with α-amylase, protease and amyloglucosidase. The
mixture is then filtered and washed by water in order to remove soluble fraction. The
insoluble fiber is washed with 95% ethanol and acetone. The insoluble fiber is the
weight after subtracting protein and ash.
AOAC 991.43
(AOAC, 2007)
Total, soluble and insoluble dietary fiber in
foods and food products, enzymatic
gravimetric method, MES-Tris buffer
Mes-Tris buffer is specifically used in this methods compared with another methods
where phosphate buffer are applied in. Still, the dried food sample is treated with α-
amylase, protease and amyloglucosidase. Soluble dietary fiber (SDF) is ethanol
precipitated, dried and weighed while the insoluble dietary fiber (IDF) is also dried
and weighed. TDF is the sum of SDF and IDF.
AOAC 992. 16
(AOAC, 2007)
Total dietary fiber, enzymatic-gravimetric
method
Grounded, dried foods are autoclaved with heat-stable amylase, amyloglucosidase,
and protease. The undigested fiber is precipitated by ethanol, filtrated and weighed
gravimetrically. Neutral detergent fiber (NDF), on the other hand, is refluxed in the
neutral detergent solution, treated with α-amylase dried and deashed. The sum of
these portions of residue is TDF.
AOAC 993.19
(AOAC, 2007)
Soluble dietary fiber in foods and food
products, enzymatic-gravimetric method
(phosphate buffer)
This method is for determination of soluble dietary fiber (SDF) in vegetables, fruit,
and cereal grains. Sample is free from starch by amylohlucosidase and free from
protein by protease. SDF is weighed gravimetrically after filtration, ethanol
precipitation and drying.
AOAC 993.21
(AOAC, 2007)
Total dietary fiber in foods and food products
with ≤2% starch, nonenzymatic-gravimetric
method
Foods with ≥10% total dietary fiber and <2% starch. Dry samples are suspended in
distilled water for 90 min at 37 oC to dissolve the soluble compounds. SDF is washed
by ethanol while the IDF is weighed gravimetrically.
AOAC 994.13
(AOAC, 2007)
Total dietary fiber (determined as neutral
sugar residues, uronic acid residues, and
Klason lignin), gas chromatographic-
colorimetric-gravimetric method (Uppsala
method)
The samples are treated with α-amylase and amyloglucosidase but without protease
treatment then subjected to 80% ethanol to gain SDF. The IDF and SDF are
hydrolyzed with 72% sulfuric acid. Neutral sugars are profiled by gas
chromatography (GC), pectic polysaccharides are quantified photometrically, Klason
lignin is weighed gravimetrically. a Source: adapted from AACC (2001).
b Source: description of the official method was summarized corresponding to the same code of the official method.
12
Some studies revealed that the washing step of SDF by 80% ethanol could
contribute some error to the accuracy of SDF due to the incompletion of precipitating
SDF or introduction of non-fiber compounds, such as organic acids (Mañas and Saura-
Calixto, 1993). Therefore, some publications reported to use dialysis tube (12,000-
14,000 molecule weight cut-off) to separate small molecules from the SDF solution
and then process SDF by freeze drying (Mañas and Saura-Calixto, 1993). In addition,
options to profile neutral sugars of DF are not only limited to use gas chromatography
(GC) but also high performance liquid chromatography (HPLC) which requires pre-
neutralization of H2SO4 hydrolysate (Villanueva-Suárez et al., 2003).
Some other studies not only have focused on the chemical characterization of
DF, but also on the extraction of SDF from food plant byproducts (i.e. orange
byproduct, peach pomace) and have studied on its rheological properties (Carme
Garau et al., 2007; Pagán and Ibarz, 1999).
2.2 Overview of wine grape pomace
2.2.1 Wine grape production and varieties in the Pacific Northwest of the United
States
Grapes are classified into wine grapes, table grapes, raisin grapes, sweet juice
grapes, and canning grapes in commerciality. The growth of grapes widely spread all
over the world and the variety grown is sensitive to the growing climate (primarily
heat summation), and directly impacts the brix/acid ratio, total acidity, tannins, and
other chemical constituents of the grapes (Winkler et al., 1974a). In US Northwest
region, Washington and Oregon grow appreciable amount of wine grapes and also
produce promising amounts of wine although the wine industry in California still
dominates domestically.
13
Table 2.3 Summary of 2008 and 2009 wine grape production and average prices
in Oregon and Washington
Varieties
Wine Grape Production Average Price
Oregon Washington Oregon Washington
2008 2009 2008 2009 2008 2009 2008 2009
Red Varieties Tons Dollars Per Ton
Cabernet Franc 200 265 2,500 2,600 1,890 1,790 1,246 1,271
Cabernet
Sauvignon 1,177 1,232 26,100 27,600 1,960 1,920 1,306 1,276
Merlot 967 1,125 25,400 24,800 1,640 1,770 1,126 1,088
Pinot Noir 17,571 21,364 800 800 2,600 2,290 1,233 870
Syrah 1,120 1,170 10,700 10,000 2,070 2,060 1,149 1,152
Semillon - - 1,200 1,200 - - 747 839
White Varieties Tons Dollars Per Ton
Chardonnay 1,630 2,244 28,000 33,400 1,640 1,530 883 857
Gewurztraminer 571 489 4,000 4,000 1,200 1,400 720 672
Pinot Gris 5,894 6,718 4,100 6,300 1,390 1,290 879 792
Sauvignon
Blanc 121 115 5,100 4,300 1,310 1,620 771 799
White Riesling 2,633 2,289 28,500 32,100 1,090 1,000 812 781
Viognier 307 367 1,300 1,300 1,780 1,740 1,007 989
Total wine grape
production or
annual average
price 34,700 40,200 145,000 156,000 2,050 1,910 1,030 989 a The table only reported the wine grapes produced more than 1000 tons per year in
Oregon or/and Washington. b
Sources: modified from USDA-NASS, Oregon (2010) and USDA-NASS,
Washington (2010).
The wine grape varieties grown in Oregon and Washington are listed in Table
2.3. Overall, total wine production in Washington in 2008 and 2009 was about 4 times
of those of Oregon whilst the average price (dollars per ton) of Oregon’s wine grapes
was two-fold as that of Washington’s wine grapes and each variety in Oregon was
priced higher than in Washington. Among red wine grapes, Pinot Noir, Cabernet
Sauvignon, and Syrah are produced more than 1,000 tons in Oregon. Meanwhile,
Merlot, Cabernet Sauvignon, Cabernet, Syrah, and Cabernet Franc are the
predominant cultivars in Washington, exceed 2,500 tons in 2008 and 2009. Pinot Noir,
well-known as one of the outstanding red varieties in the world (Winkler et al., 1974b),
14
is identified as signature wine grape in Oregon (>21,000 tons in 2009), followed by
Cabernet Sauvignon and Syrah (>1,100 tons). Inversely, Cabernet Sauvignon and
Merlot that produce the two mostly world-famous red wines (Winkler et al., 1974b),
predominantly grow in Washington, followed by Syrah, Cabernet Franc, and Semillon.
In this research, Pinot Noir, Cabernet Sauvignon, and Merlot were chosen as three red
wine grape varieties. The berries of Pinot Noir are descriptively small to medium, oval,
and black colored. They ripen very early. However, Cabernet Sauvignon’s berries are
spherically small in black color and the skins are tough. They usually ripen in late
season. Further, the berries of Merlot are round shaped in medium size with bluish
black skins (Winkler et al., 1974b).
Regarding to the white wine grape varieties, Pinot Gris is the major one in
Oregon, followed by White Riesling and Chardonnay. Nevertheless, Riesling and
Chardonnay are the major white wine grapes in Washington which are tenfold as those
in Oregon. Furthermore, Gewurztraminer, Pinot Gris, Sauvignon Blanc, and Viognier
are also flourished in Washington. In this study, however, Muller Thurgau and Morio
Muscat were the two objective white wine grape varieties studied. Across the United
States, Oregon is the leading producer of Muller Thurgau since it needs cool climate to
maintain the sugar level. The berries of Muller Thurgau are Blanc and ripen early
(Schmitz, 2000). The berries of Morio Muscat are white in color, round in shape, and
ripen in the middle season (Pool, 2000).
2.2.2 Winemaking procedures (Jackson, 2000a,b)
It has been well recognized that the winemaking in the world can trace back to
6,000 years ago while America only have about 400 years winemaking history (Vine
et al., 1997). Winemaking has been improved in the recent couple of centuries. Except
the grape varieties, growing regions climates, harvesting time, and wine making
procedures vary depending on the requirements of consumers. To make table wines,
grapes are harvested, stemmed, crushed, macerated, pressed, fermented and the
fermented liquid undergos some post fermentation steps before bottling, such as
malolactic fermentation, maturation, natural clarification, and stabilization (Jackson
15
2000a). Overall, the major differences of red winemaking and white winemaking are
that pressing for red winemaking is after fermentation and maceration while it is
before fermentation for white winemaking, which directly contributes to the different
chemical composition of the red wine grape pomaces (RWGP) from the white wine
grape pomaces (WWGP).
Harvesting grapes, stemming, and crushing should be conducted as soon as
possible to avoid juice browning and microbial contamination. In the step of stemming,
leaves and grape stalks are removed from grape clusters while stems, sometimes, may
be left in red winemaking procedures in order to get extra red color, astringent taste,
and tannins from the stems. Crushing is carried out immediately after stemming to
avoid the browning of released juices and microbial contaminations caused by the
damage of grape berries in the previous two steps. Crushing is a procedure for helping
the release of juices from the grape berries. After crushing, maceration, fermentation,
and pressing are done before getting RWGP, while WWGP is obtained after
maceration and pressing. Towards completing the alcoholic fermentation, malolactic
fermentation is carried out. Several post-fermentation treatments are also performed
before bottling, such as maturation and natural clarification, finishing, and
stabilization.
2.2.2.1 Red wine process (Jackson, 2000a)
Red must, the combination of juices, seeds and skins (may also include some
stems) are left for fermentation and maceration for red wine. Maceration in red
winemaking is for extraction of the pigment and tannin from the must. Time of
maceration differs upon the styles of red wine, and usually endures about 3 to 5 days.
Along with maceration, fermentation of must is carrying out simultaneously. Yeast,
usually Saccharomyces cerevisiae and Leuconostoc oenos, ferments the sugars in the
wine must and coverts sugar to ethanol. Meanwhile, the production of ethanol
enhances the extraction of the red pigments (anthocyanins) and the solubility of aroma
compounds from must, the metabolism of yeast enables to produce various aroma
compounds for the wine. The temperature for red wine fermentation is often from 24
16
to 27 oC, but not necessarily universal, which enables to extract more phenolic
compounds from the wine must. After fermentation, pressing is conducted mainly by
hydraulic force. RWGP is obtained after pressing. Since the red winemaking process
goes through the fermentation which complicated yeast metabolisms involved in, the
chemical composition of RWGP differs from that of WWGP. For red wine, malolactic
fermentation is often necessary due to the high acidity after completion of
fermentation. Except reducing the acidity of wine, malolactic fermentation also
modifies the sensory characters and influences the stabilities of microorganisms.
2.2.2.2 White wine process (Jackson, 2000a)
Unlike red wine process, maceration of white grapes is kept as short as
possible, maximum a couple of hours. The juice oxidation is the major reason for
shortening the maceration time in white wine production. WWGP is obtained after
juice pressing. Juice is then subjected to fermentation at low temperature (8-15 o C).
What is more, due to the relatively higher pH value for white wine production, adding
of malic acid to white wine before malolactic fermentation is required in some cases.
2.2.3 Wine grape pomace (WGP)
WGP, the byproduct from winemaking, is mainly composed of seeds and skins
while it is possible to contain stems in RWGP depending on winemaking processes. A
very few literature resources are available on the specific chemical composition of
WGP other than their polyphenolic compounds.
WGP is a rich source of polyphenols in nature. The distribution of polyphenols
in skins and seeds are different. Grape skins are rich in anthocyanins (only in RWGP
skins), hydroxycinnamic acids, flavonol glycosides, and flavonols while flavonols
mainly existed in grape seeds. Overall, 13 anthocyanins (only in RWGP skins), 11
hydroxylbenzoic and hydroxycinnamic acids, and 13 catechins and flavonols were
found in WGP (Kammerer et al, 2004). Therefore, WGP is a diverse and rich source
of polyphenols, enabling their bioactivities, such antioxidant, antimicrobial, and anti-
cancer activities.
17
Early, some simple measurements on the chemical composition of WGP other
than polyphenols were performed by the researcher in the New York State (Kinsella et
al., 1974; Rice, 1976) in order to evaluate potential utilizations of WGP. 6 varieties of
WWGP and 5 varieties of RWGP were investigated in terms of their percentage of
solid residue (%), moisture content (%), seeds (%), sugar (%), tartrate (%), crude fiber
(%), nitrogen (%), phosphorus (%), ash (%), and seed oil (%). Overall, the tartrate (%)
of white varieties in average was higher than that of the red varieties. On the other
hand, crude fiber (%) of RWGP was higher than that of WWGP. Grape seed oil,
however, existed in both of RWGP and WWGP with the close percentage. As the
study of chemical composition of WGP getting further, carbohydrates or even specific
DF from WGP were studied. Walter (1985) fractionated the hydrocolloidal fractions
from WGP (cv. Seyval) by using water, NaOH, EDTA, and HCl independently, and
obtained some basic data for extracting hydrocolloids from WGP. Meanwhile,
researches on dietary fiber and polyphenols of WGP were carried out in Europe
(Saura-Calixto et al, 1991; Valiente et al., 1995; Bravo and Saura-Calixto, 1998). With
more attention to nutritional properties of dietary fiber from WGP, the studies in
Europe employed protease to treat WGP and then expressed the results in terms of
Klason lignin (%), SDF (%), IDF (%), resistant protein (%), uronic acid (%), and
polyphenols (%) (Saura-Calixto et al., 1991; Valiente et al., 1995; Bravo and Saura-
Calixto, 1998).
Although the wine production is continuously climbing, little information on
the WGP from North America is available. Chemical composition data of WGP is
essential when comes to develop new applications of this highly valuable byproduct.
Therefore, this study aimed to investigate the chemical composition (majorly DF and
polyphenols) of five varieties of WGP (cv. Merlot, Carbernet Sauvignon, Pinot Noir,
Muller Thurgau and Morio Muscat) which are predominant in the Pacific Northwest
region of the United States.
2.2.4 Antioxidant activity of WGP
18
Since “French paradox” was discovered in 1992 (Renaud et al., 1992),
numerous studies have investigated the bioactive functions of WGP. Following that,
the studies on the health functions of red wine, especially the antioxidant functions of
red wine, have been continuously carried out. Those positive findings stimulated the
researches on the antioxidant activity of WGP in which high amounts of polyphenols
are left after pressing. Many in vitro methods have been applied to evaluate the
antioxidant activity of WGP, such as Folin-Ciocalteau assay (FC assay) for total
phenolic compounds, 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay and Trolox
equivalent antioxidant capacity (TEAC) assay for free radical scavenging ability,
ferric reducing antioxidant power (FRAP) for reducing power, and oxygen radical
absorbance capacity (ORAC) for antioxidant capacity (Ruberto et al., 2007; Kataliníc
et al., 2010; Monagas, et al., 2006). Kataliníc (2001) reported that the antioxidant
activities of white grape skins were less than those in red grape skins in respect of
DPPH and FRAP assay. The relatively high antioxidant activity (162-495 mg vitamin
E equivalent/g DM) (Llobera and Cañellas, 2007) of WGP compared with other plant
wastes enables WGP to be named as ADF. Except for the in vitro experimental
methods, in vivo methods for testing the antioxidant activity of WGP in animals and
humans were also performed. Feeding rats with ADF from WGP could effectively
reduce the apoptosis by modulating “glutathione redox system and endogenous
antioxidant enzymes” (Lópex-Oliva et al., 2010). ADF from WGP was also given to
adult panelists and the study found that ADF from WGP was able to reduce the blood
pressure and significantly decrease the lipid profile, therefore reduced the risk of
cardiovascular disease (Jiménez, et al., 2008).
2.2.5 Antimicrobial activity of WGP
Many researches on the antimicrobial activities of plant based products
concluded that phenolics, polyphenols, flavonoids, flavonols, and tannins are among
the major sources of antimicrobial agents produced in plants (Cowan, 1999). However,
there is no identical finding about whether WGP is more effective on preventing the
growth of gram-negative or gram-positive microorganisms. For instance, Kataliníc
19
(2010) reported that the WGP skin extracts inhibited the growths of both gram-
negative and gram-positive microorganisms while some other studies found that the
gram-positive organisms are more susceptible to WGP extracts (Corrales et al., 2009;
Özkan et al., 2004). Furthermore, it was suggested that some organic acids, such as
tannin acid, malic acid, and tartaric acid, performed antimicrobial activities in grape
juice and wine (Daglia et al., 2007; Kim et al., 2008). The organic acids left in WGP
may still contribute to a part of antibacterial function, but requires further
investigations.
2.2.6 Extraction of phenolic compounds from WGP
Efforts on improving the yield and quality of phenolic compounds from WGP
have been dedicated to solvent types, ratio of liquid-solvent, temperature, and time
(Pinelo, et al., 2006a). Usually, methanol, ethanol, acetone, or ethylacetate is mixed
with water in various ratios (Spigno et al., 2007; Spigno and De Faveri, 2007). It is
also suggested to use acidified solvents (i.e. acetic acid, hydrochloric acid) (Spigno
and De Faveri, 2007) to improve the release of phenolic compounds from plant cell
walls thus to yield higher amounts of phenolic compounds (Krygier and Sosulski,
1982; Maisuthisakul and Gordon, 2009). Temperature is another important factor
influencing the yield of phenolic compounds from WGP. High temperature but not
exceeding 50 oC might enable a higher recovery of phenolic compounds from WGP
(Cacace and Mazza, 2003; Pinelo, et al., 2006b). The liquid-solid ratio is also studied
to optimize the extraction efficiency while reducing the consumption of organic
solvents. The reported extraction time varied between 5 min to 60 h and was related to
other extraction conditions (Spigno et al., 2007; Spigno and De Faveri, 2007).
Although many publications on extracting phenolic compounds from WGP have been
published, no agreement on the most appropriate protocol has been reached. Therefore,
it is necessary to investigate the most appropriate extraction procedure of WGP skins
in this project so that a similar protocol can be applied to extract phenolic compounds
in the future.
20
2.2.7 Utilizations of WGP
Utilizations of WGP have been widely studied (Table 2.4). The products
developed from WGP included fertilizers, organic acids, organic solvents, dietary
supplements, ethanol, animal feeds, and food additives. WGP may also be used as the
substrates for solid-state fermentation of organic acids, organic solvents, pullulan, and
enzymes. The possible applications of WGP for food and nutraceutical industries, as
well as other possible utilizations are discussed below.
21
Table 2.4 Treatment and usage of grape wastes, physicochemical properties and
their utilization Pomace Treatment Physicochemical
characteristics
Utilization
Grape waste Composting of grape waste
and hen droppings
Organic matter
content
Fertilizer for corn
seed
Grape seed
and skin
extracts
Fractionation of grape seed
and skin extracts from
grape waste
Phenol content Dietary supplements
for disease prevention
Grape waste Gasification of waste
products from grape
Concentrations of
unused residues
Gas production for
heating purpose
Pressed grape
skin
Composting of solid waste
and wastewater
Organic matter
content
Fertilizer
Wine pomace
and grape
seeds
Lyophilisation and
extraction of flavanols
Flavanol content Dietary supplements,
production of
phytochemical
Grape marc,
stalks and
dregs
Lyophilisation and
extraction of polyphenols
Polyphenolic content Source of flavanols
Grape skins,
seeds and
stems
Acidolysis of a polymeric
proanthocyanidic fraction
of grape pomace in the
presence of cysteamine
Flavanol content Source of flavanols
Grape seed
extract (GSE)
Pre-and post-mrtem use of
grape seed in feeding
experiment
Phenol content Feedstuff for dark
poultry meat
Grape skin
pulp
Fermentation by
Aureobasidium pullulan
Ethanol precipitate Pullulan production
Grape seeds Solid-state cultivation by
Pleurotus sp.
Lignocellulosic
content
Laccase production
Grape
pomace
Solid-state cultivation by
Pleurotus sp.
Pruning content, high
phenolic components
and total sugars
Feedstuff for animals
Wastewater Electrodialysis Tartaric acid content Additive in medicines
and cosmetics,
acidulant compound
in soft drinks
Wastewater Electrodialysis at 60 oC Tartaric acid and
malic acid content
Food and
pharmaceutical
industries
Source: Adapted from Arvanitoyannis et al. (2006).
Regarded to nutraceuticals, grape seeds, grape extracts, and red wine powder
(skins of RWGP) are the basic WGP products in the US market, in which was reported
to include 22 types of grape seed products, 5 types of grape extract and 7 types of red
22
wine skin powder (Shrikhande et al., 2000). Phenolic compounds and unsaturated fatty
acids (especially from grape seed oils) are the major functional groups in those dietary
supplements. Recent research revealed the possibly medical utilization of WGP
because the content of polyphenols might contribute to prevent tooth decay (Kish,
2008).
In food industry, WGP has been evaluated as potential natural food colorants
based on its high amount of anthocyanins (Sriram et al., 1999). With the increasing
demands for functional foods, the possibility for WGP as food ingredients has been
elucidated in several studies. Saura-Calixto (1998) evaluated the possibility of using
WGP as “antioxidant dietary fiber” which could be directly applied on various food
products (i.e. dairy, cereal, and confectionary products) to enhance the DF content and
nutritional value in foods. In a recent study, the WGP powder was applied in minced
chicken for reducing the lipid oxidation of raw and cooked chicken hamburgars
(Sáyago-Ayerdi et al., 2008). In beverage industry, after distillation and fermentation
of WGP, it comes with “Grappa”, a popular and historical alcohol-beverage
originating from Italy (Bovo et al., 2009). WGP popsicle has been reported to be
successfully made in laboratory (Ishimoto, et al., 2009). For bakery applications, the
dry WGP skin powder has also been commercially sold as bakery flour in Canada
(Vinifera Fod Life CanadaTM
, Jordan, ON, Canada). The product development of
WGP is promising, and not many WGP-incorporated food products are available in
the consumer market yet. Therefore, more studies on using WGP for food applications
require to be further executed.
Another potential application of WGP is as edible or biodegradable packaging
materials. WGP based biocomposite boards have been successfully developed in our
laboratory (Park et al., 2010; Jiang et al., 2011) and their application in foods and
other agricultural applications as packaging containers are under the way. More fruit
and vegetable byproducts, such as cranberry pomace, mango puree, apple puree, have
been applied to form edible films and coatings because their extracts naturally contain
DF and other film forming materials, as well as some bioactive compounds (Park and
23
Zhao, 2006; Du et al., 2008a,b; Azeredo et al., 2009). It is believed that WGP extracts
can be used as the basic film forming materials to obtain edible films and coatings
with antimicrobial and antioxidant properties based on their functional constitutes.
2.3 Edible films and coatings
2.3.1 History of edible films and coatings
Edible films and coatings are formed by food grade materials, either made as a
thin-layer sheet as films or as a part of food products when coated directly on the
surface of food (Debeaufort et al., 1998). According to the historical record, wax
coatings were applied on citrus fruits to prevent the fruit from dehydration in China in
12th
and 13th
centuries; the soy protein layers from boiled soy milk, called “Yuba”,
were applied to preserve foods in Asia in 15th
century; edible films were used to coat
meat products to avoid shrinkages in 16th
century; sucrose was employed to coat the
surfaces of tree nut products in 19th
century (Debeaufort et al., 1998). In more recent
history, edible films and coatings have been applied on a wide range of food products
to improve their quality (i.e. appearance, flavor, aroma, nutritional value) and extend
shelf-life since 1930s (Debeaufort et al., 1998). Nowadays, with the increasing
consumer demands for high quality food products, studies on innovating edible films
and coatings with diverse functionalities and excellent mechanical properties continue.
2.3.2 Functions of edible films and coatings for food applications
Edible films and coatings play significant roles on food. Their functionalities
may be summarized below.
(a) Edible films and coatings may have mechanical properties that can prevent
the physical damage to a certain extent (Han and Gennadios, 2005). However, the
mechanical properties of edible films and coatings are usually weaker than those of
plastic films (i.e. LDPE, HDPE, EVOH, PVC, and PET) (Han and Gennadios, 2005).
Therefore, the study on improving mechanical properties needs to be enhanced and
different film forming materials should be continuously investigated to gain better film
mechanical properties.
24
(b) Edible films and coatings are able to regulate mass transfer between foods
and the storage environment. Mass transfer can cause adverse effects on food texture,
aroma, appearance, nutrient value and food safety (Wu, 2002; Lin and Zhao, 2007).
Edible films and coatings can control the exchange of moisture, gas, lipid, aroma and
flavor compounds from foods to the environment depending on the nature of film
forming materials, and storage conditions (i.e. temperature and relative humidity)
(McHugh et al, 1996; Han and Gennadios, 2005). It has been widely recognized that
lipid-based edible films and coatings (waxes, lacs and fattic acids) perform better
moisture barrier property than that of polysaccharide-based and protein-based edible
films (Bourlieu, et al., 2009). Conversely, lipid-based edible films and coatings are
less capable to control lipid and gas exchange compared with polysaccharide-based
and protein-based films and coatings (Han and Gennadios, 2005; Bourlieu et al., 2009).
Generally, in fresh-cut and minimally processed fruits and vegetables, edible coatings
are employed to reduce the moisture loss and control respiration rate of fruits and
vegetables (Han and Gennadios, 2005; Vargas, et al. 2008). In cereals and bakery
products, edible coatings are applied to control the moisture migration among the
different food ingredients in the products (Han and Gennadios, 2005). For the high-fat
food products, such as fish (Duan et al., 2010), meat (Caprioli, et al, 2009) and cheese
(Cerqueira, et al., 2009), edible films and coatings are widely used to prevent lipid-
oxidation and reduce moisture loss (Kerry et al., 2006). In confectionary industry,
edible coatings (wax, cellulose gum, whey proteins) are applied for candies and
chocolates to prevent “stickiness, agglomeration, moisture absorption, and oil
migration” (Debeaufort et al., 1998).
Owing to their capacities of regulating mass transfer, edible films and coatings
can also enhance some food processing steps (Han and Gennadios, 2005). For instant,
edible coatings applied on fruits and vegetables can reduce the leak-out of soluble
compounds from foods and prevent the dehydrating solutions get inside foods during
osmotic dehydration (Han and Gennadios, 2005). They can also lower the absorption
25
of oil during the frying process, as well as decrease the loss of flavor compounds
during lyophilization (Han and Gennadios, 2005).
(c) Edible films and coatings can carry active substances to enhance the
nutrient value and/or microbial safety of food products. For fruits and vegetables,
functional ingredients that are usually added to edible coatings may include
antimicrobial agents (essential oils, potassium sorbate, chitosan), antioxidants (citric
acid, ascorbic acid, N-acetylcysteine), texture enhancers (calcium chloride, calcium
gluconate, calcium lactate), and nutraceuticals (calcium gluconate, vitamin E, ascorbic
acid, Bifidobacterium lactis) (Rojas-Graü et al., 2009). In meat products, active
ingredients including bacteriocin (nisin, lacticin, pediocin), enzymes (glucose oxidase),
organic acids, essential oils, and herb extracts may be incorporated into coatings for
meat preservation (Coma, 2008).
For food applications, the active compounds should be effectively released
from edible films and coatings (Han and Gennadios, 2005). The release speed and
amount depend on the interactions between the active compounds and other film
forming materials, and the releasing condition (temperature, pH, solution, etc.) (Al-
Musa, et al., 1999; Roger, 2006).
2.3.3 Film forming materials
In general, the polysaccharides (i.e. pectin, carrageenan, starch) (Maftoonazad
et al., 2006; Park and Zhao, 2006; Seol et al., 2009; Kim et al., 2002), proteins (i.e.
corn zein, wheat gluten, soy protein, collagen, gelatin) (Cuq et al., 1998), and lipids
(i.e. fatty acids, waxes, resins, acetylated glycerides) (Bourlieu et al., 2009) are three
basic matrix for forming edible films and coatings (Han and Gennadios, 2005). It has
been widely recognized that protein and polysaccharide based films are of relatively
high water vapor permeability and stronger mechanical properties while lipid-based
films are inverse in both properties (Ruan et al., 1998). To overcome the shortage of
each basic film forming material, edible films made from blended materials have been
developed lately, such as fatty acid-hydroxypropyl methylcellulose edible films
(Hagenmaier and Shaw, 1990), essential oil-alginate-apple puree edible films (Rojas-
26
Graü et al., 2007), hydroxypropyl methylcellulose-lipid edible coatings (Perez-Gago et
al., 2003), and soy proteins-high methoxyl pectin films (Piazza, et al., 2009).
Plasticizers, defined as “substantially nonvolatile, high boiling, non-separating
substance, which change the physical and/or mechanical properties of other materials”
(Banker, 1966) are usually added as film forming materials to reduce the brittleness
(Park and Zhao, 2006) and control the mouth feelings of the films (Guilbert, 1986;
Kim et al., 2002). However, plasticizers can enhance the diffusion of small molecules
since the addition of plasticizers decrease the glass transition temperature of films
(Bourlieu et al., 2009). Water, sucrose, corn syrup, propylene glycol, sorbitol,
mannitol, xylitol, and glycerol are all used as plasticizers in edible films and coatings
(Kim et al., 2002; Han and Gennadios, 2005).
In composite edible films and coatings (emulsion composite or bi-layer
composite) containing lipids, emulsifiers (lecithin, Tweens, Spans) are commonly
added to the film forming solutions to help the dispersion of lipid droplets in film
forming solutions (Bravin et al., 2004; Han and Gennadios, 2005; Pérez-Gago and
Krochta, 2005).
Overall, lipids, proteins and polysachcarides compose the major structures of
edible films and coatings, plasticizers improve the flexibility, and emulsifiers specially
assist lipids incorporating with proteins and polysaccharides. Other functional
ingredients such as antimicrobials, antioxidants, texture enhancers, and nutraceuticals
may also be incorporated into edible films and coatings for enhancing the
physiological, antimicrobial and nutritional properties of the films and coatings.
2.3.4 Overview of edible films and coatings originated from plant materials
2.3.4.1 Sources of plants
The three basic film forming materials (polysaccharides, proteins, lipids) are
partially from plant materials. Polysaccharides are abundant in plant materials.
Polysachcarides, such as pea starch (Corrales et al., 2009), pectin (Schultz et al., 1949;
Oms-Oliu et al., 2008; Pérez et al., 2009), cellulose derivatives (carbomethylcellulose,
27
hydroxypropylcellulose, and methyl cellulose) (Hagenmaier and Shaw, 1990; Ayranci
and Tunc, 2001; Forssell et al., 2002), and xylan from agricultural byproducts (i.e.
hulls, sorghum, and wheat straw) (Kayaserilioğlu et al., 2003), have been studied to
form edible films and coatings. Plant proteins are also exploited to be good film
forming materials. Soy protein and soy protein isolate (Piazza et al., 2009; Denavi et
al., 2009; Atarés et al., 2010), corn zein (Kim et al., 2004), and pea protein isolate
(Choi and Han, 2002) based films have shown good mass barriers and strong
mechanical properties with or without the incorporation of other film forming
materials. Plant is also a rich source of lipids. Rice bran wax has been used to coat
candy and coumarone indene resin for fresh citrus fruits (Bourlieu et al., 2009). In
addition, most parts of fatty acids are originally from plant materials, such as oleic
acid from “olive, peanut, palm, corn, rapeseed and canola” and linoleic acid from
“soybean, sunflower, corn and cottonseed” (Rhim and Shellhammer, 2005).
Bioactive compounds produced by plant materials have also been added into
edible films and coatings in recent years. Essential oils which “are volatile, natural
compounds with a strong odor and formed by aromatic plants as secondary
metabolites” (Guimarães et al., 2010), have been added to provide both antioxidant
and antimicrobial functions. For instance, cinnamon and ginger essential oils were
added to the soy protein isolate based films (Atarés et al., 2010); tea tree essential oil
was incorporated into hydroxypropyl methylcellulose to form edible films (Sánchez-
González et al., 2009); allspice, cinnamon, and clove bud essential oils were added
into apple puree based edible films (Du et al., 2009). Plant extracts added edible films
have also been studied, such as ginseng extract added alginate films (Norajit et al.,
2010), grapefruit seed extract added algae (Gelidum corneum) films (Lim et al., 2010),
gooseberry extract added chitosan films (Mayachiew and Davahastin, 2010), and
aqueous oregano and rosemary extracts added gelatin films (Gómez-Estaca et al.,
2009a). More plant extracts may be applied with better technologies to extract
bioactive compounds from plant tissues. While the addition of bioactive compounds
enhance the functionality of edible films and coatings, it may alter their mechanical
28
and mass barrier properties (Sánchez-González et al., 2009; Du et al., 2009;
Mayachiew and Davahastin, 2010; Gómez-Estaca et al., 2009a; Atarés et al., 2010;
Norajit et al., 2010; Lim et al., 2010). Therefore, in this project, the WGP extract
based edible films were evaluated in respects to their physicochemical, mechanical,
nutritional and antimicrobial properties.
The method of utilizing plant tissues film forming materials varies in published
studies. Many studies have used commercially purified plant based materials as basic
film forming materials, while some other studies directly used the raw plant tissues
without purification. For example, mango puree, apple puree, and tomato puree have
been directly utilized as film forming materials (Du et al., 2008a,b; Rojas-Graü et al.,
2007; Sothornvit and Rodsamran, 2008). In our previous study, cranberry pomace
extracts that contain pectin, cellulose, polyphenols, organic acids, minerals and other
nutrient compounds were successfully applied to form edible films (Park and Zhao,
2006). WGP has similar chemical composition as that of cranberry pomace, thus was
used as basic film forming material in this project.
2.3.4.2 Antimicrobial property of edible films and coatings originated from plant
materials
Except for the mechanical, moisture and gas barrier properties, antimicrobial
property of edible films and coatings are increasingly studied with the intension to
extend the shelf-life of food products without the addition of other chemical
preservatives. One of the major studies in developing antimicrobial films and coatings
is to incorporate essential oils to enhance the antimicrobial properties. Due to their
numerous chemical constituents (terpenes, aromatic compounds and terpenoides),
essential oils are cytotoxic to a wide range of microorganism (Bakkali, et al., 2008).
Therefore, after properly incorporating with other film forming materials, essential
oils incorporated films have shown good antimicrobial activity against the growth of
Listeria monocytogenes (Ponce et al., 2008; Du, et al., 2009), Salmonella enterica and
Escherichia coli O157:H7 (Du et al., 2009).However, only a few publications studied
the antimicrobial activities of phenolic compounds incorporated films. Galangal
29
extracts added chitosan films effectively decreased the growth of Staphylococcus
aureus (Mayachiew et al., 2010). Grape seed extracts added soy protein isolate film
inhibited the growth of Salmonella typhimuriu, Escherichia coli O157:H7, and
Listeria monocytogenes (Sivarooban et al., 2008). With the increasing attention on
food safety, it is necessary to investigate the antimicrobial property of edible films and
coatings with natural plant bioactive compounds.
2.3.4.3 Antioxidant property of edible films and coatings originated from plant
materials
Along with the antimicrobial activity, antioxidant activity of edible films has
also attracted great research interests, not only due to its ability to elongate the shelf-
life but also to provide extra health benefits. Majority of studies on the antioxidant
activity of edible films have focused on incorporating essential oils and aqueous
soluble plant extracts, such as phenolic compounds and organic acids into film
forming materials. Essential oils (oregano and pimento) added milk protein based
films were applied to beef muscle for preventing lipid oxidation (Oussalah et al.,
2004). Borage extracts increased the antioxidant activities of gelatin based edible films
compared to the ones with α-tocopherol and butylated hydroxytoluene (BHT)
according to the in vitro antioxidant analysis (FRAP, ABTS, and iron (II) chelation
activity) (Gómez-Estaca, 2009b). Ginseng extracts (Norajit et al., 2010), grape seed
extracts (Lim et al., 2010), and gooseberry extracts (Mayachiew and Davahastin, 2009)
were employed as antioxidant bioactive compounds in edible films. However, limited
study is available about the WGP skins extracts and their antioxidant properties in
edible films or coatings, Therefore, part of this project has targeted to evaluate the
antioxidant property of the WGP (skins) extract based edible films.
2.3.4.4 Applications of edible films and coatings originated from plant materials
in foods
Plant based or plant extract added edible films and coatings have been applied
on different food products to extend shelf-life. Fresh-cut or minimum processed fruit
and vegetable products tend to be easily spoiled by microorganisms as well as
browning discoloration (Rojas-Graü et al., 2009). Plant based polysaccharides,
30
proteins, and lipids are the basic coating forming materials to extend shelf-life of these
products by building up gas barrier (oxygen, carbon dioxide, ethylene, and volatile)
and moisture barrier functions (Maria et al., 2008; Lin and Zhao, 2007). Plant
originated or plant extract added coatings are also applied on meat products for
preventing lipid oxidation and spoilages (Kerry et al., 2006). Plant based or plant
extract added edible films are used as food wraps, topping decorators and kids’ snacks
(Origami Foods LLC., Stockton, CA, USA). Mango puree (Azeredo et al., 2009),
apple puree (McHugh and Senesi, 2000), and tomato puree (Du et al., 2008b) have
been made into food wraps for various commercial applications.
The development of WGP based edible films in this study aimed to maximize
the utilization of WGP as film forming material to obtain films with promising
mechanical and water barrier properties. Therefore, the films could be applied as a
packaging material to extend shelf-life and enhance flavor and nutrition of wrapped or
coated food products.
2.4 Conclusion
Wine grape pomace is abundant in the Pacific Northwest of the United States
as a wine processing byproduct. Studies to investigate its chemical composition are
essential before developing their value-added applications. Limited information on the
dietary fiber and polyphenols of WGP skins (vinifera L. cv. Morio Muscat, cv. Muller
Thurgau, cv. Cabernet Sauvignon, cv. Pinot Noir and cv. Merlot) from the Pacific
Northwest of the United States is available. Therefore, it is necessary to design the
protocol for determining the dietary fiber and associated polyphenols and obtain the
chemical composition data of these WGP skins.
Furthermore, WGP extract based edible films are anticipated to have
antioxidant and antimicrobial functions according to its high content of polyphenols
and organic acids. However, a very few study has developed WGP extract based
edible films and investigated their antimicrobial and antioxidant properties
simultaneously. The release of the bioactive compounds from film matrix is worthy of
31
studying as it is directly related to the application of the edible package. Therefore,
this project also evaluated the feasibility of using WGP extracts to make edible films
by investigating their physicochemical, nutritional and antimicrobial properties.
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43
CHAPTER 3
Chemical Composition of Dietary Diber and Polyphenols of Five Different
Varieties of Wine Grape Pomace skins
Qian Deng, Michael H. Penner, Yanyun Zhao*
Department of Food Science and Technology, 100 Wiegand Hall,
Oregon State University, Corvallis, OR 97331, USA
*correspondent author: Email: [email protected]
To be submitted to Food Research International
3-1750 The Queensway Suite 1311, Toronto, Ontario, M9C 5H5, Canada
44
Abstract
The skins of two white wine grape pomace (WWGP) and three red wine grape
pomace (RWGP) from US Pacific Northwest were analyzed for their dietary fiber (DF)
and phenolics composition. DF was measured by gravimetric-enzymatic method with
sugar profiling by HPLC-ELSD. Insoluble DF composed of Klason lignin (7.9-36.1%
DM), neutral sugars (4.9-14.6% DM), and uronic acid (3.6-8.5% DM) weighed more
than 95.5% of total DF in all five WGP varieties. WWGP was significantly lower in
DF (18.8-30.3% DM) than those of RWGP (51.1- 56.3%), but extremely higher in
soluble sugar (55.8-77.5% DM vs. 1.3-1.7% DM) (p<0.05). Soluble polyphenols were
extracted by acidified 70% acetone and measured spectrophotometrically. Compared
with WWGP, RWGP had higher values in total phenolics content (21.4-26.7 mg
GAE/g DM vs. 11.6-15.8 mg GAE/g DM) and DPPH radical scavenging activity
(32.2-40.2 mg AAE/g DM vs. 20.5-25.6 mg AAE/g DM) (p<0.05). The total flavanol
and proanthocyanidin contents were ranged from 31.0 to 61.2 mg CE/g DM and 8.0 to
24.1 mg/g DM, respectively for the five WGP varieties. This study demonstrated that
the skins of WGP can be ideal sources of DF rich in bioactive compounds.
Key words: wine grape pomace (WGP), dietary fiber (DF), polyphenols, radical
scavenging activity (RSA)
45
Introduction
The United States is the 4th
largest wine producing region in the world. It is
estimated that over 4 million metric tons of grapes are harvested and processed into
wine products in the US annually (USDA, 2006) and that amount is expected to
increase. Wine grape production in Washington and Oregon was 156,000 and 40,200
tons in 2009, respectively; their production being 2nd
and 4th
among all states (USDA-
NASS, 2010). Therefore, tremendous amounts of wine grape pomace (WGP) are
available annually in the Pacific Northwest region of the United States. WGP is
primarily composed of seeds, skins and stems, and is commonly used for the
extraction of grape seed oils (Mattick and Rice, 1976), the production of citric acid,
methanol, ethanol, and xanthan via fermentation (Hang and Woodams, 1985; Hang, et
al., 1986; Couto and Sanromán, 2005), and as animal feed (Saunders and Takeda,
1982). The large amounts of WGP available at relatively low cost provide an
opportunity for value-added product development through innovative technologies.
Dietary fiber (DF), defined as “edible parts of plants or analogous
carbohydrates that are resistant to digestion and absorption in the human small
intestine with complete or partial fermentation in the large intestine” (AACC, 2001), is
abundant in plant products such as fruits, vegetables, and grains. DF is widely
recognized as being a beneficial component of a healthy diet, its consumption being
correlated with reductions in risks associated with cardiovascular disease, cancer, and
diabetes (Cho and Dreher, 2001). Furthermore, grape skins, which comprise, on
average, 82% of the wet weight of WGP (Jiang et al., 2011), contain multiple types of
polyphenols, including 39 types of anthocyanins, hydroxycinnamic acids, catechins,
and flavonols (Kammerer et al., 2004). These polyphenols have been claimed to have
antioxidant activity (González-Paramás et al., 2004) and inhibit low-density
lipoprotein oxidation (Yildirim et al., 2005).
The DF content of WGP from grape varieties in Spain, such as Manto Negro,
Cencibel, and Airén, has been published (Valiente et al., 1995; Bravo and Saura-
Calixto, 1998; Llobera and Cañellas, 2007). However, little is known of the
46
composition of WGP resulting from the processing of grapes common to the US
Pacific Northwest. These varieties include Pinot Noir, which accounts for >50% of the
total wine grape production in Oregon (USDA-NASS, 2010), and Cabernet Sauvignon
and Merlot, the latter two being the top red wine varieties in Washington (USDA-
NASS, 2010). The chemical composition of WGP is known to vary depending on the
grape cultivar, growth climates, and processing conditions. Therefore, the aim of this
study was to characterize the DF and polyphenol fractions of WGP skins common to
the US Pacific Northwest. The information obtained from this study will be helpful in
the development of value added products derived from such WGP. In this study, skins
of WGP were abbreviated as WGP.
Materials and Methods
Sample preparation
Two white wine grape pomace (WWGP) samples, Vitis vinifera L. cv. Morio
Muscat and cv. Muller Thurgau, were donated by a private winery in Corvallis,
Oregon, USA. One red wine grape pomace (RWGP), Vitis vinifera L. cv. Cabernet
Sauvignon, was from a commercial winery in Kennewick, Washington, USA. The
other two RWGP samples, Vitis vinifera L. cv. Pinot Noir and cv. Merlot, were
received from the Oregon State University Research Winery (Corvallis, OR, USA).
All WGP samples were processed in fall 2008, packed in the polyethylene
terephthalate pails (Ropak Corp., Cincinnati, OH, USA) and stored at -24 oC until used.
Dietary fiber samples were prepared from the skins contained within the WGP
using the procedures of Park et al. (2009). Briefly, WGP was thawed at room
temperature, stems and seeds were removed manually and the remaining WGP skins
were ground in a disintegrator (M8A-D, Corenco, Inc., Sebastopol, CA, USA) to pass
a 0.11 mm mesh screen. The resulting preparation was then dried in an environmental
chamber (T10RS, Tenney Environmental, Williamsport, PA, USA) at 10% RH and 70
oC for 48 hours. The dried WGP was then milled (Thomas Scientific, Swedesboro, NJ,
47
USA) to pass a 20-mesh screen. The resulting powders were stored in Ziploc® storage
bags (S.C. Johnson & Son, Inc., Racine, WI, USA) at -24 oC until used.
Analysis of ash, fat and crude protein contents
Ash, fat and crude protein contents of the WGP powders were determined at a
certified commercial laboratory (Bodycote Testing Group, Portland, OR, USA) and
the results were expressed as percentage of dry matter (DM).
Analysis of soluble sugars
A representative 0.5 g sample of WGP powder in a 35 mL centrifuge tube was
extracted three times in succession with 25 mL of 80% ethanol for 15 min at room
temperature in an ultrasonic unit (Branson B–220H, SmithKline Co., Shelton, CT,
USA) (AOAC 994.13, 2007). Each extraction was terminated by centrifugation
(10,000 × g for 10 min) and collection of the resulting supernatant. The combined
supernatants, from the three extractions, were evaporated at 50oC under vacuum by a
rotary evaporator (Brinkmann Instruments, Westbury, NY, USA) to remove ethanol
and then diluted to 50 mL with water. The sugar content was then determined by
thoroughly mixing 1 ml of the soluble sugar-containing solution with 2 mL 75%
H2SO4 and 4 mL anthrone reagent (anthrone reagent consisted of 0.5 mg anthrone
(Alfa Aesar, Ward Hill, MA, USA) in 250 mL 75% H2SO4, incubating the reaction
mixture at 100 oC for 15 min, cooling to room temperature, and measuring absorbance
at 578 nm (UV160U, Shirmadzu, Kyoto, Japan) (Gerhardt, 1994). Absorbance values
were converted to “glucose equivalents” using a calibration curve prepared with a D-
glucose (Sigma Chemical Co., MO, USA) as specified above. Results were expressed
as a percent of WGP DM.
Fractionation of extractable pectins
WGP total extractable pectins (TEP) were fractionated into water soluble
pectin (WSP), chelator soluble pectin (CSP), and hydroxide soluble pectin (HSP) as
described by Silacci and Morrison (1990). WGP powder, 1.0 g, was first homogenized
(PT 10-35, Kinematica, Littau, Switzerland) in 20 g deionized water for 10 min. The
48
homogenate was then filtrated (Whatman No.1 filter paper) and the retentate and
filtrate collected. WSP was obtained as the precipitate that resulted from the addition
of 95% ethanol to the filtrate (filtrate: 95% ethanol = 1:5) and then allowing it to stand
overnight in the refrigerator. CSP was obtained from the water extracted residue by
first boiling the residue with 95% ethanol for 10 min and then doing three successive
extractions of the resulting residue with 50 mL, 20 mM disodium ethylenedinitrilo
tetraacetic acid (Na2-EDTA, Mallinckrodt Baker, Inc., Phillipsburg, NJ, USA), pH 8.0.
Following each extraction the suspension was filtered and the filtrates combined. The
residue obtained from the Na2-EDTA extractions was then extracted with 50 mL of 50
mM NaOH for 15 min at room temperature; the suspension was filtered and the filtrate
collected for measurement of HSP.
WSP, CSP, and HSP were quantified as galacturonic acid equivalents (GUAE)
(Spectrum Chemical, Co., Gardena, CA, USA) based on a colorimetric assay (AOAC
994.13, 2007) using galacturonic acid for preparation of the calibration curve. Briefly,
250 µL boric acid-sodium chloride solution (content) and 250 µL of sample (or
standard) were mixed with 4 mL of 96% H2SO4 and incubated at 70 oC for 40 min.
Next, 200 µL of dimethyphenol reagent (100 mg of 3, 5-dimethyphenol in 100 mL of
glacial acetic acid; Sigma Chemical Co., MO, USA) was added with mixing and the
absorbance read at 400 nm and 450 nm, respectively.
Determination of dietary fiber
Separation of soluble dietary fiber (SDF) and insoluble dietary fiber (IDF).
A representative 0.5 g sample of WGP powder was defatted by two successive
extractions with 25 mL petroleum ether for 10 min in an ultrasonic water bath at room
temperature; the liquid and solid phases being separated by centrifugation for 10 min
at 10,000 × g. The defatted residue was then extracted three times in succession with
80% ethanol, as described above, to remove soluble lower molecular weight
saccharides. The resulting residue was dried at 40 oC for 16 h. The dried residue was
then treated with 0.0275 mL protease (P-5459, Sigma Chemical Co., MO, USA) in
49
0.05 M phosphate buffer, pH 7.5, for 30 min at 60 oC (AOAC, 1985; Bravo and Saura-
Calixto, 1998). Liquid and solid phases were separated by centrifugation at 10,000 × g
for 10 min. The supernatant was saved for determination of SDF. The residue was
washed with two portions of 10 mL deionized water; the supernatants from these
washings were combined with the supernatant obtained following the protease
treatment for determination of SDF. The resulting residue was washed first with 95%
ethanol and then twice with acetone followed by drying at 40 oC for 16 h (Prosky et al.,
1985). This residue was used for IDF analyses.
Analysis of SDF. In order to prevent error caused by precipitating dietary fiber
with ethanol (Mañas, 1994), SDF was separated by exhaustive dialysis of the SDF-
containing liquid against deionized water using tubing with a molecule weight cutoff
of 12,000-14,000 (Spectrum Laboratories, Inc., Rancho Dominguez, CA, USA) in 1 L
of DI water in the refrigerator. DI water was changed at 4, 16, 28, 30, and 36 h,
respectively and the dialysis was finished at 48 h of which the conductivity of
dialysate was around 2-6 µS/cm, very close to the value of DI water (~1 µS/cm). The
dialyzed SDF preparation was freeze-dried and then acid hydrolyzed in 6% sulfuric
acid at 121 oC for 1 h (Bravo and Saura-Calixto, 1998). Uronic acids (UA) in the
resulting hydrolysate were quantified by colorimetry as described above. Neutral
sugars (NS) were determined by HPLC following neutralization by addition of
calcium carbonate. D-(+)-glucose, D-(+)-xylose, D-(+)-galatose, D-(+)-arabinose, and
D-(+)-mannose were employed as standards. HPLC was done using a Shimadzu 20A
series instrument equipped with Shimadzu-LT II evaporative light scattering detector
(ELSD) (Shimadzu, Columbia, MD., USA) and a Biorad Aminex HPX-87P column
(Bio-Rad Laboratories, Hercules, CA, USA). The nitrogen pressure of the ELSD was
maintained at 50.6 to 52.0 psi and column temperature at 85 oC. Distilled/deionized
water was used as the mobile phase with a flow rate of 0.6 mL/min and injection
volume of 20 µL (Sluiter, et al., 2008). The sum of NS and UA was taken as the
amount of SDF in WGP. All the results were expressed as percentage per DM.
50
Analysis of IDF. The dry residue was hydrolyzed in a two-stage manner. The
first stage involves the addition of 3 mL 72% sulfuric acid to the residue, with stirring,
and subsequent incubation at 30 oC for 1 h. The second stage consists of diluting the
first-stage hydrolysate to 2.5% sulfuric acid by the addition of 84 g deionized water,
followed by incubation of the resulting suspension at 121 oC for 1 h. The hydrolyzed
mixture is then filtrated (fritted crucible; Pyrex® 30 mL M, Corning, Inc., USA). The
filtrate is used for quantifying UA and NS as described above. The crucible containing
the residue is used for the gravimetric determination of Klason lignin (KL) as
described by Sluiter et al. (2008). KL determination was based on mass measurements
following drying the residue at 105 oC for 16 h and ashing for 5 h at 525
oC. Resistant
protein (RP) in the WGP powder, defined as the protein after protease treatment and
acid hydrolysis, was determined by the micro-Kjedahl method using a nitrogen-to-
protein conversion factor of 6.25 (AOAC 960.52, 1995). IDF was the total of NS, UA
and KL, and expressed as percentage per DM.
Determination of bound condensed tannins (CT)
Residue analogous to that used for the IDF analyses, prepared from 0.5 g WGP
as discussed above, was used for determination of bound CT using the method
described by Reed (1982). The residue was incubated with 50 mL 5% HCl-butanol
(v/v) in a capped Erlenmeyer flask at 100 oC for 3 h. After cooling to room
temperature, the absorbance of the liquid phase at 553 nm was determined. Standards
for CT are not commercially available; therefore, a CT preparation from red wine
grape skin (~80.4% by weight CT) was used as the standard in companion analyses
(Kennedy and Jones, 2001). The extinction coefficient used for quantification was
based on incubating a 5.0 mg sample of the CT standard with 10 mL 5% acid-butanol
at 100 oC for 30 min and subsequently determining the liquid phase absorbance at 553
nm. The bound CT of WGP was expressed as percentage per DM.
51
Extraction and quantification of soluble phenolic compounds
Phenolics extraction from fresh WGP. Two methods were compared for
extraction of soluble phenolics in WGP. Frozen WGP were ground to a fine powder in
liquid nitrogen and subsequently used for extraction experiments as WGP. Preliminary
data (not shown), as well as a survey of the literature (Spigno and Faveri 2007; Spigno,
et al., 2007), indicated that 1:4 (w/v) ratio of WGP to solvent was sufficient for
extraction of phenolic compounds, thus both methods were carried out at this ratio. In
the first method (method “A”), WGP was extracted with 0.1% HCl/70% acetone/29.9%
water (v/v/v) by placing the suspension in an ultrasonic unit for 1 h at room
temperature; the temperature of the ultrasonic bath was kept below 45 oC by
exchanging water when necessary. The liquid and solid phases were then separated by
centrifugation at 10,000 × g for 15 min. This procedure was done three times per
sample (total of three extractions per sample). The combined supernatant from the
three extractions was concentrated on a rotary evaporator at 40 oC under vacuum and
then brought to 50 mL with deionized water and stored at -70 oC until analyzed. In the
second method (method “B”), the solvent was 70% acetone/30% water and the
extraction was done in an environmental shaker at room temperature with constant
agitation (125 rpm). This procedure was done two times per sample (total of two
extractions per sample). The combined supernatant from the two extractions was
concentrated, brought to volume and stored as in method “A”. The thawed
supernatants resulting from extraction methods A and B (referred to below as
“extracts”) were used as the starting material for the analysis of total phenolics,
antiradical scavenging activity, total flavanol, extractable proanthocyanidins, and
anthocyanins.
Analysis of total phenolic content (TPC). The total phenolic content of
extracts was measured using the Folin–Ciocalteu (FC) reagent-based colorimetric
assay as described by Singleton and Rossi (1965). Phenolic content was calculated as
gallic acid equivalents (GAE) and reported as mg/g DM. Briefly, 0.5 mL appropriately
diluted extract (or gallic acid standard at 0, 50, 100, 150 or 200 ppm; Sigma Chemical
52
Co., MO, USA) was mixed with 0.5 mL of 2N FC reagent (Sigma Chemical Co., MO,
USA) and 7.5 mL deionized water and allowed to stand for 10 min at room
temperature; then 3 mL of 20% (w/v) Na2CO3 (Sigma Chemical Co., MO, USA) was
added to the reaction mixture and it was placed in a 40 oC water bath for 20 min. After
the 20 min reaction period, the samples were cooled to room temperature and the
absorbance measured at 765 nm.
Analysis of antiradical scavenging activity (RSA). The RSA of extracts was
determined by the 1,1–diphenyl–2–picryhydrazyl (DPPH)-based assay (Kasel Kogyo
Co. Ltd, Tokyo, Japan) using ascorbic acid as the calibration standard and reported as
mg ascorbic acid equivalents (AAE) per g DM (Brand-Williams, 1995). Briefly, 0.5
mL appropriately diluted extract (or ascorbic acid standard at 0, 0.01, 0.02, 0.03, 0.04
mg/mL, Mallinckrodt Baker Inc., Phillipsburg, NJ, USA) was mixed thoroughly with
1.5 mL of DPPH–methanol reagent (9 mg DPPH in 100 mL methanol) and allowed to
stand at room temperature for 5 min prior to measuring the solutions absorbance at
517 nm.
Determination of total flavanol content (TFC). The total flavanol content of
extracts was determined by the vanillin (Alfa Aesar, Ward Hill, MA, USA)
colorimetric assay (Price, 1978) using (+)-catechin hydrate (Sigma Chemical Co., MO,
USA) as the calibration standard. A 1.0 mL aliquot of appropriately diluted extract (or
the catechin standard at 0, 0.06, 0.12, 0.18, 0.24, 0.30 mg/ml) was mixed with 5.0 mL
vanillin reagent (0.5% vanillin in 4% HCl-methanol, w/v). This mixture was allowed
to react for 20 min at 30 oC and then the absorbance measured at 500 nm. The blank,
included in each assay, was treated as above except the blank-vanillin reagent
contained no vanillin. Concentrations were determined based on taking the difference
between the absorbance of the corresponding assay and blank samples. TFC was
expressed as mg catechin equivalents (CE) per g DM.
Determination of extractable proanthocyanidins (PAC). Extractable PAC
was measured by the colorimetric assay of Porter (1986) using a red wine grape skin
CT powder as the calibration standard. Briefly, 0.5 mL extract (or standard solution)
53
was mixed (vortexed) with 3 mL acid butanol (50 mL 12 N HCl with 950 mL n-
butanol) and 0.1 mL iron reagent (2% ferric ammonium sulfate (EMD Chemicals,
USA) in 2 N HCl). The mixture was then placed in boiling water for 50 min followed
by the measurement of its absorbance at 553 nm. Extractable PAC was expressed as
mg CT equivalents per g DM.
Analysis of anthocyanin content (ACY). The ACY content of extracts was
determined by the pH differential method (Guisti and Wrolstad, 2001). Briefly, extract
was diluted to the same extent in 0.025 M potassium chloride (final pH = 1.0) and in
0.4 M sodium acetate (final pH = 4.5) and the absorbance of the two solutions was
measured at 520 nm and 700 nm. A solution of malvidin-3-glucoside (Mvd-3-glu),
molar absorptivity of 28,000 L/cm/mol and molar mass of 529 g/mol, was used as the
calibration standard. ACY was calculated as:
ACY mg/liter =
((A520 – A700)pH 1 – (A520 – A700)pH 4.5 × 529 × dilution factor × 1000)/28000
(Thimothe et al., 2007), and expressed as mg Mvd-3-glu equivalents/g DM.
Data Analysis
All analyses, with the exception of those specified as being done by a
commercial laboratory, were done in triplicate. Results were expressed as mean ± SD.
Pair t-test was used to compare the differences between the two phenolic extraction
methods (A and B). One way ANOVA was used to analyze the differences among
WGP samples based on LSD test at 95% confidence level (SAS 9.1, SAS Institute Inc.,
Cary, NC, USA).
Results and Discussion
Ash, protein and fat
Overall, RWGP had higher crude protein, fat and ash contents than those of
WWGP (Table 3.1), which was consistent with the results found by Baumgärtel et al.
54
(2007). Among WWGP varieties, Muller Thurgau had higher values in crude protein
and fat but lower value in ash than those in Morio Muscat. Regarding to RWGP
varieties, Cabernet Sauvignon had relatively high crude protein, fat and ash content, an
indication of high amino acids and minerals in the pomace sample.
Table 3.1 Crude protein, fat and ash content of five varieties of wine grape
pomace (WGP) Composition
(% DM)
Muller
Thurgau
Morio Muscat Cabernet
Sauvignon
Merlot Pinot Noir
Crude protein 6.54 5.38 12.34 11.26 12.13
Fat 2.64 1.14 6.33 3.35 4.74
Ash 2.53 3.31 7.59 7.19 6.17
Soluble sugar
In this study, soluble sugar was defined as mono- or di-saccharides dissolving
in 80% ethanol. The two WWGP varieties had significantly (p<0.05) higher soluble
sugar contents than those of RWGP, about 56% for Muller Thurgau and 78% for
Morio Muscat (Table 3.2), while it was between 1.3-1.7% for RWGP. The high
soluble sugar content of WWGP was not reported in previous publications and
probably due to different winemaking procedures applied and different varieties of the
wine grape. WWGP was obtained right after pressing juice while RWGP was after
fermented with juice for several days in order to extract color and polyphenols. Hence,
the unfermented juice residue attaching to WWGP rendered the considerably higher
amount of soluble sugar compared with those in RWGP. Soluble sugar content of
RWGP from this study was relatively lower than those commercial RWGP in Europe,
such as Cencibel, Manto Negro, and Blauer Portugieser (Bravo and Saura-Calixto,
1998; Llobera and Cañellas, 2007; Baumgärtel et al., 2007), but closer to the data
reported in US wine grape varieties, such as cv. Concord, Ives, Baco Noir, and
Cascade (Rice, 1976).
55
Table 3.2 The major carbohydrate fractions of wine grape pomace (WGP) Composition
(% DM)
Muller
Thurgau
Morio
Muscat
Cabernet
Sauvignon
Merlot Pinot Noir
Soluble sugar 55.77±2.12b 77.53±1.01
a 1.71±0.49
c 1.34±0.92
c 1.38±0.93
c
Total dietary
fiber 28.01±1.36
e 17.28±0.21
d 53.21±0.38
b 51.09±0.58
c 56.31±1.47
a
Different superscripts in rows indicated the differences among five WGP varieties
based on LSD test (p<0.05).
Extractable pectins
Overall, RWGP had higher total extractable pectin (TEP) content (50.6 to 56.4
mg GUAE/g DM) than that of WWGP (32.3 to 41.2 mg GUAE/g DM) (figure 3.1)
(p<0.05). However, the similar trend was not observed in respect to individual fraction
of the pectin (Figure 3.1), in which the distributions of three pectin fractions varied
depending on the variety of WGP. Among the three fractions of extractable pectins,
the highest proportion was CSP (79.47% to 94.50% of TEP). CSP of RWGP was
higher than that of WWGP. Cabernet Sauvignon was of the highest value of CSP
(about 50 mg GUAE/g DM), followed by Merlot and Pinor Noir. For WWGP, CSP of
Muller Thurgau was 10 mg GUAE/g DM, higher than that of Morio Muscat (p<0.05).
Relatively, only small amounts of WSP and HSP were observed in both WWGP and
RWGP.
WSP of Merlot was significantly (p<0.05) higher than the values in any other
varieties, about 4.5 mg GUAE/g DM followed by Pinot Noir with a value of about 2.5
mg GUAE/g DM. The smallest proportion was HSP with the lowest amount in Morio
Muscat (0.42 mg GUAE/g DM) and the highest amount in Merlot (0.89 mg GUAE/g
DM). Insufficient studies on fractionating pectic polysaccharides of WGP into WSP,
CSP and HSP have been reported. According to Silacci and Morrison (1990),
winemaking procedures did not have largely impact on the distributions of three
fractions except that the WSP might be reduced due to the compression step, and the
high CSP indicated that the largest proportion of extractable pectin is cell wall bound
pectin.
56
(a) Water soluble pectin (WSP)
(b) Chelator soluble pectin (CSP)
(c) Hydroxide soluble pectin (HSP)
0
1
2
3
4
5
6
Muller Thurgau Morio Muscat Cabernet Sauvignon
Merlot Pinot Noir
WS
P (
mg
GU
AE
/g D
M)
d
cd
a
b
20
25
30
35
40
45
50
55
Muller Thurgau Morio Muscat Cabernet Sauvignon
Merlot Pinot Noir
CS
P (
mg
GU
AE
/g D
M)
c
d
ab
bc
0
0.5
1
1.5
Muller Thurgau Morio Muscat Cabernet Sauvignon Merlot Pinot Noir
HS
P (
mg
GU
AE
/g D
M)
b
c bc
a
b
57
(d) Total extractable pectins (TEP)
Figure 3.1 Fractionation of extractable pectins (water soluble, chelator soluble,
hydroxide soluble pectin and total extractable pectins) from wine grape pomace
(WGP) expressed as mg GUAE/g DM. Different letters on the top of each column
showed the differences among the varieties (p <0.05).
Dietary fiber
TDF (Table 3.2) was the predominant composition in the RGWP but not in the
WWGP in which soluble sugar took the largest proportion. TDF of 51.1% to 56.3% on
dry matter in the RWGP were similar to those reported by Veliente et al. (1995) and
Bravo and Saura-Calixto (1998) (about 50% to 60% of TDF).
Major fraction of TDF was insoluble dietary fiber (IDF) which dominated up
to 98.5% of the TDF (Table 3.3). RWGP had significantly (p<0.05) higher NS content
than those of WWGP. Regarding to NS in IDF, Merlot had at least 9% more than
other two RWGP varieties, and Muller Thurgau had 46% higher amount of NS than
that of Morio Muscat. Among the NS, glucose was of the highest amount for all five
WGP varieties, followed with xylose, while arabinose was traced to be the lowest
amount. Since cellulose structured by large amount of glucose subunits, substantial
amount of glucose existing in IDF indicated that cellulose was the major constituent of
IDF in the WGP. This finding was consistent with the results by Bravo and Saura-
Calixto (1998) and Veliente et al. (1995). The ratio of xylose to galactose varied from
0.8 in Morio Muscat to 2.1 in Merlot, which, to some extent, indicated the amount of
hemicellulose in IDF. This ratio is within the range of other findings (Valiente et al.,
0
10
20
30
40
50
60
70
Muller Thurgau Morio Muscat Cabernet Sauvignon
Merlot Pinot Noir
TE
P (
mg
GU
AE
/g D
M)
cd
a ab
58
1995; Bravo and Saura-Calixto, 1998). Based on the fact that the major constituent of
hemicellulose in grape skins is xyloglucans, structured by the glucan backbone linked
with β (1→4) linkage and 75% of glucose siding with xylose and 35% galactose
(Thompson and Fry, 2000), it was predictable that a promising amount of
hemicellulose is in the WGP skins.
59
Table 3.3 Dietary fiber content in five different wine grape pomace (WGP)
KL, Klason lignin; NS, neutral sugar; UA, uronic acid; IDF, insoluble dietary fiber;
SDF, soluble dietary fiber. IDF = NSIDF + UAIDF +KL; SDF = NSSDF + UASDF; TDF =
SDF + IDF. Data were expressed as mean ± SD. The different superscripts in the same
row were significant different (p <0.05).
Dietary fiber Muller
Thurgau
Morio
Muscat
Cabernet
Sauvignon
Merlot Pinot Noir
IDF
%
DM
Glucose 4.59±0.57c
3.16±0.07d
7.33±0.51b
9.16±0.46a
8.43±0.39a
Xylose 0.91±0.09c
0.45±0.04d
1.94±0.11b
2.13±0.11a
2.09±0.08a
Galactose 0.67±0.05c
0.54±0.03d
0.97±0.02b
1.02±0.03b
1.17±0.08a
Arabinose 0.43±0.04c
0.34±0.02d
0.76±0.05a
0.75±0.05a
0.58±0.06b
Mannose 0.49±0.05c
0.36±0.01d
1.48±0.04a
1.54±0.05a
1.12±0.07b
NSIDF 7.08±0.80d
4.85±0.04e
12.25±0.39c
14.59±0.39.a
13.39±0.37b
UAIDF 4.81±0.66cd
3.64±0.21d 8.53±0.82
a 6.62±0.25
b 5.14±0.70
c
NSIDF +
UAIDF
11.89±1.20c
8.49±0.17d
20.78±0.79a
21.20±0.61a
18.50±0.94b
KL 15.40±0.27d 7.94±0.06
e 31.62±0.48
b 28.38±0.67
c 36.06±0.75
a
IDF 27.29±1.46d
16.44±0.24e
52.40±0.40b
49.59±0.34c
54.59±1.57a
SDF
%
DM
Glucose 0.20±0.07c
0.15±0.04c
0.33±0.03b
0.38±0.1ab
0.43±0.39a
Xylose 0.02±0.00c
0.02±0.01c
0.03±0.01ab
0.04±0.01a
0.02±0.00c
Galactose 0.12±0.04ab
0.13±0.04a
0.07±0.03b
0.15±0.06a
0.18±0.02a
Arabinose 0.07±0.02c
0.11±0.01b
0.07±0.02b
0.13±0.02ab
0.16±0.01a
Mannose 0.05±0.01bc
0.01±0.00c
0.05±0.06bc
0.09±0.03b
0.22±0.08a
NSSDF 0.46±0.13c
0.42±0.10c
0.54±0.08c
0.78±0.22b
1.00±0.10a
UASDF 0.43±0.06b
0.26±0.03c
0.27±0.04c 0.73±0.07
a 0.72±0.06
a
SDF 0.72±0.14c
0.84±0.07c
0.81±0.06c
1.51±0.14b
1.72±0.15a
(NSIDF + NSSDF) %
DM
7.54±0.74d
5.27±0.11e
12.79±0.34c
15.37±0.48a
14.39±0.29b
(UAIDF + UASDF) %
DM
5.07±0.64cd
4.07±0.25d
8.80±0.79a
7.34±0.2b
5.72±0.72c
TDF % DM 28.01±1.36
e 17.28±0.21
d 53.21±0.38
b 51.09±0.58
c 56.31±1.47
a
60
Uronic acid (UA) ranged from 3.6-8.5% (Table 3.3) in the IDF fraction,
illustrated that a large proportion of pectic polysaccharides composed of cell wall
materials. Similarly, UA of RWGP was 7% to 134% higher than that of WWGP.
Cabernet Sauvignon had the highest UA value, while Muller Thurgau had the lowest
among the five varieties. Since UA is the backbone of pectic polysaccharides in plant
cell walls, it was concluded that RWGP generally had higher contents of pectic
polysaccharides. By considering the neutral sugar profiling data, it could be confirmed
that WGP skins contain a large amount of homogalacturonan (HG) consisting of
backbone galacturonic acids with some xylose and glucose and a small amount of
hairy pectic polysaccharides (rhamnogalacturonan I and rhamnogalacturonan II)
(Arnous and Meyer, 2009).
Unlikely in IDF, SDF took only small portion of TDF in all WGP varieties. In
SDF, the NS was mainly associated with UA to form the pectic polysaccharides. The
NS and UA values varied from 0.4% to 1.0% DM and 0.3% to 0.7% DM, respectively.
NS in SDF was the lowest in Morio Muscat (~0.4% DM) and the highest in Pinot Noir
(1.0% DM), and UA in SDF were the highest in Merlot and Pinot (0.73% DM and
0.72% DM, respectively) while the lowest in Morio Muscat and Cabernet Sauvignon
(0.26% DM and 0.27% DM respectively). Glucose was the predominant sugar in all
five WGP varieties with the highest in Pinot Noir (0.43% DM) and the lowest in
Morio Muscat (0.15% DM), but only 0.02% to 0.04% xylose was detected in the SDF
of WGP. The NS data in SDF did not agree with the findings by Bravo & Saura-
Calixto (1998) in which only arabinose was detected in SDF of WGP, but agreed with
the data from Valiente et al. (1995). That the UA value close to NS might indicate that
the hairy pectic polysaccharides were the major portion of the SDF. The low UA
content detected in the WGP differed from the work by Bravo and Saura-Calixto
(1998) and Valiente et al. (1995), possibly owing to the discrepancies in grape berry
maturity at the time of harvest, the WGP varieties, and the winemaking procedures.
Considerable amount of Klason lignin (KL) was observed in IDF fraction of
the WWGP, but significantly lower than those in the RWGP (Table 3.3). Pinot Noir
61
possessed the highest amount of KL among RWGP, 4.4% and 7.7% higher than that of
Cabernet Sauvignon and Merlot, respectively. In terms of WWGP, KL of Muller
Thurgau was nearly double than that of Morio Muscat. The ratios of KL to TDF
ranged from 54.9% in Morio Muscat to 64.0% in Pinot Noir. Differences in
lignifications of cell wall materials and wine grape variety contributed to the various
KL values in the WGP. The high KL content in IDF of WGP skins make it suitable for
various applications, such as phenolic resins and adhesives (Stewart, 2008). In this
study, resistant proteins (RP) and bound condensed tannins (CT) were also quantified
(Table 3.4).
Table 3.4 Bound condensed tannins (CT) and resistant protein (RP) of insoluble
dietary fiber (IDF) residue (% DM)
Expectedly, the CT and RP values generally had the same trend as KL. Both
bound CT and RP values of the RWGP were higher than those of WWGP. Pinot Noir
had the highest amount of bound CT (19.89% DM) and the highest RP (4.92% DM),
while Morio Muscat was the lowest in both values, 6.04% DM for bound CT and 1.50%
DM for RP.
The ratios of bound CT to RP were quite close among different WGP varieties,
from 3.57 to 4.45, indicated that the protein-binding capacity of polyphenols in the
WGP skins was not affected by the WGP varieties. The CT-RP matrix formed because
the polymeric polyphenols were able to precipitate proteins in the plant cell wall
during the grape berry maturation. The CT to RP ratios detected in this study were
higher than those described by Bravo and Saura-Calixto (1998), but close to that
Muller
Thurgau
Morio
Muscat
Cabernet
Sauvignon Merlot Pinot Noir
Bound CT % DM 8.53±0.33c 6.04±0.09
d 16.14±0.24
b 16.26±0.58
b 19.89±0.32
a
RP % DM 2.30±0.01b
1.50±0.04b
4.52±0.10a
3.65±0.03a
4.92±0.57a
Bound CT : RP 3.71 4.03 3.57 4.45 4.04
RP % of crude
protein
35.17 27.88 36.63 32.42 40.56
62
published by Llobera and Cañellas (2007). The bound CT in the WGP was
significantly higher than those in fruit, fruit peels and dark chocolates (Goñi et al.,
2009).
In addition, the percentage RP of crude protein (Table 3.4) was 40.6% for
Pinot Noir, 36.6% for Cabernet Sauvignon, 32.4% for Merlot, 35.2% for Muller
Thurgau, and 27.9% for Morio Muscat, lower than those described in the previous
studies, such as 80.6% in RWGP skins (Cencibel) and 78.6% in WWGP skins (Airén)
(Bravo and Saura-Calixto, 1998). In this study, RP was determined after protease
treatment and sulfuric acid hydrolysis while the RP in those publications were
measured right after protease digestion, which contributed the lower ratios of RP to
crude protein than literatural values.
Effect of different extraction conditions on the soluble phenolic compounds
Results in the soluble phenolic compounds extracted by using two different
extracting methods were reported in Table 3.5. Method A was superior to method B in
almost all phenolic compounds for all varieties of WGP (p<0.05) except TPC of
Morio Muscat and Merlot, ACY of Cabernet Sauvignon and Pinot Noir, and PAC of
Morio Muscat. By using method A, TPC values of RWGP and Muller Thurgau
increased from 39% to 110%, RSA and TFC values increased from 53% to 125% and
24% to 65%, respectively for all the WGP varieties, and PAC values also remarkably
increased from 49% to 130% for all varieties except for Morio Muscut. This study
demonstrated the influence of extraction conditions on the yield of phenolic
compounds from WGP. First, the ultrasound assisted extraction yielded higher content
of polyphenols than the extraction carried out at room temperature with low speed
shaking. This observation agreed with results from previous publications (Kalia et al.,
2008; Khan, Abert-Vian et al., 2009). Secondly, HCl acidified aqueous solvent
extraction enhanced the extraction yield of TPC and RSA but little on ACY (p value
was from 0.010 to 0.180), which was consistent with the findings from Maisuthisakul
and Gordon (2009) and Vatai et al. (2009). Increased TPC and RSA values as a result
of acid hydrolysis solvent extraction might be explained by the fact that the hydrolysis
63
step helped the release of polyphenols from plant cell wall materials (Krygier and
Sosulski, 1982; Maisuthisakul and Gordon, 2009). Finally, the three times extraction
might also promote the efficiency of phenolics extraction from the WGP.
Soluble polyphenols
Since method A worked better than method B in respect to extraction of
phenolic compounds, only results from method A are discussed here. TPC values of
RWGP were significantly higher than those of WWGP (p < 0.05) due to the lack of
ACY in WWGP. No markedly difference in TPC values between Muller Thurgau and
Morio Muscat was observed. Among RWGP, TPC of Pinot Noir was lower than that
in Merlot and Cabernent Sauvignon (p<0.05) (Table 3.5), which may be attributed to
the thinner fruit skin of Pinot Noir, retaining less TPC.
Table 3.6 shows the total polyphenols reported in previous publications on
wine grape pomace, grape berry, and other fruit byproducts. TPCs detected in this
study were within the range of the published data (9.7 to 54.0 mg GAE/g DM). The
higher TPC values in other publications were owing to inclusion of grape seeds into
WGP which possessed higher content of phenolics. The TPC values of fresh wine
grape berry were also reported in Table 3.6. TPC of Pinot Noir was 38.4 mg/g based
on fresh weigh, which was significantly higher than value from this study (21.4 mg
GAE/g DM). The reduction of TPC in WGP was due to the extraction of polyphenols
from red wine grape skins into wine via winemaking processing.
64
Table 3.5 Soluble phenolic compounds of different varieties of wine grape pomace (WGP) extracted by method A and B
TPC, total phenolics content; RSA, DPPH radical scavenging activity; ACY, monomeric anthocyanins; TFC, total flavanol content;
PAC, extractable proanthocyanidins content. Different superscripts shown within the method A column indicated the differences
among WGP varieties based on LSD test (p<0.05); the comparison between method A and B employed pair t – test (p<0.05) to
compare the differences in the values of the same parameter obtained by the two methods.
WGP TPC
mg GAE/g DM
RSA
mg AAE /g DM
ACY
mg Mvd– 3 – glu /g DM
TFC
mg CE/g DM
PAC
mg/g DM
A B p A B p A B p A B p A B p
Muller
Thurgau 15.8±0.3c 11.4±0.9b 0.001 25.6±1.9c 11.4±1.2b <0.001 - - - 58.9±1.6a 40.3±5.0a 0.004 19.4±2.3b 10.5±2.6b 0.010
Morio
Muscat 11.6±1.0c 11.4±1.7b 0.870 20.5±3.3c 10.9±1.6b 0.01 - - - 31.0±1.7c 25.0±3.3c 0.050 8.0±1.3c 7.7±1.5b 0.750
Cabernet
Sauvignon 26.7±1.8a 12.7±0.5b <0.00
1 39.7±2.6a 17.7±2.3a <0.001 0.89±0.02b 0.85±0.03b 0.140 54.3±4.6a 42.0±3.7a 0.022 17.2±2.3b 7.7±1.8b 0.005
Merlot 25.0±3.6a 18.3±3.0a 0.060 40.2±1.9a 19.7±1.7a <0.001 1.42±0.14a 1.09±0.03a 0.010 61.2±5.0a 37.0±2.6ab 0.001 24.1±3.8a 15.8±1.2a 0.020
Pinot Noir 21.4±4.3ab 11.2±0.2b 0.010 32.2±4.5b 21.1±2.3a 0.019 0.29±0.01c 0.26±0.03c 0.180 42.6±5.4b 32.5±3.1bc 0.050 11.9±1.4c 8.0±1.0b 0.016
65
Table 3.6 The documentary values of total phenolic compounds from wine grape
pomace (WGP), fresh wine grape berry, and other fruit byproducts
Byproducts Total phenolic content Bibliography
WGP and/or WGP skins
(varieties)
RWGP, skins (Cabernet
Sauvignon, Merlot and Pinot
Noir)
21.4 to 26.7 mg GAE/g DM This study
WWGP, skins (Muller
Thurgau and Morio Muscat)
11.6 to 15.8 mg GAE/d DM This study
Wine grape marc (Cabernet
Sauvignon and Merlot)
20.2 mg GAE/g DM Vatai, Škerget & Kenz, 2009
RWGP (Manto Negro) 26.3 mg GAE/g DM Llobera & Cañellas, 2007
WWGP, skins (Cencibel) 37.6 mg GAE/g DM Bravo & Saura – Calixto,
1998
RWGP, skins (Airén) 44.8 mg GAE/g DM Bravo & Saura – Calixto,
1998
WWGP and WWGP skins
(Roditis)
48.3 and 9.7 mg GAE/g DM
Makris, Boskou &
Andrikopoulos, 2007
RWGP and RWGP skins
(Agiorgitiko)
54.0 and 36.25 mg GAE/g
DM
Makris, Boskou &
Andrikopoulos, 2007
WWGP (Prensal Blanc) 34.9 mg GAE/g DM Llobera & Cañellas, 2008
Fresh wine grape berry
Red wine grape, skins (Pinot
Noir)
38.4 mg/g FW * Mané, et al., 2007
White wine grape, skins
(Muscat of Alexandria)
1.2 mg GAE/g FW Poudel, Tamura, Kataoka &
Mochioka, 2008
Other fruit byproduct
Cider apple pomace 6.46 ×10-3
mg GAE/g DM Suárez, et al., 2010
5.5 × 10-3
to 10.9 × 10-3
mg
GAE/g DM
García, Valles & Lobo, 2009
Orange peel 2.76 mg GAE/g FW Khan, et al., 2010
Acerola residues (juice
production)
6.81 mg GAE/g DM Oliveira, et al., 2009
Pineapple residues (juice
production)
2.75 mg GAE/g DM Oliveira, et al., 2009
Passion fruit residues (juice
production)
1.03 mg GAE/g DM Oliveira, et al., 2009
Strawberry residues (juice
production)
59.77 mg GAE/g extract
corresponding to the yield of
extract 17.1% DM
Peschel, et al., 2006
Pear residues (juice
production)
12.90 mg GAE/g extract
corresponding to the yield of
extract 11.4% DM
Peschel, et al., 2006
66
Table 3.6 (continued)
Byproducts Total phenolic content Bibliography
Red beet residues (juice
production)
91.74 mg GAE/g extract
corresponding to the yield of
extract 20.1% DM
Peschel, et al., 2006
Cranberry juice pomace About 11.0 mg GAE/g DM Vattem, Lin & Shetty, 2005
Blueberry pomace
Blueberry juice pomace 11.9 mg GAE/g DM
Su & Silva, 2006
Blueberry wine pomace 10.9 mg GAE/g DM
Su & Silva, 2006
Blueberry vinegar pomace 2.3 mg GAE/g DM Su & Silva, 2006
* TPC was quantified by HPLC instead of Folin-Ciocalteu assay.
WGP: wine grape pomace; WWGP: white wine grape pomace; RWGP: red wine
grape pomace; GAE: gallic acid equivalents.
Similar to the TPC values, the RSA values of RWGP were higher than those of
WWGP (p<0.05). RSA of Pinot Noir was of the lowest among the RWGP, while no
difference between two WWGP varieties. The TPC and RSA values were linearly
correlated (R=0.989) (Figure 3.2), which was in agreement with the results by
Dunonne et al. (2009).
Figure 3.2 Correlation between RSA and TPC (R=0.989), RSA and TFC
(R=0.653), and RSA and PAC (R=0.667) for five WGP varieties.
Anthocyanins (ACY) was not detected in the WWGP but in the RWGP with
the highest content in Merlot (1.42 mg Mal-3-glu/g DM) followed by Cabernet
0
10
20
30
40
50
60
70
20 25 30 35 40RSA (mg AAE/g DM)
TPC (mg GAE/g DM) TFC (mg CE/g DM)
PAC (mg/g DM)
67
Sauvignon (0.89 mg Mal-3-glu/g DM) and Pinot Noir (0.29 mg Mal-3-glu/g DM). As
was stated previously, due to the thicker skins of Merlot and Cabernet Sauvignon,
ACY values of those two varieties were significantly higher than that of Pinot Noir.
Reported ACY values in grape pomace varied depending on the extraction and
analytical methods and grape varieties. Thimothe et al. (2007) reported that ACY of
Pinot Noir and Cabernet Franc was 5.9 and 67.2 mg mal-3-glu/g of lyophilized extract,
respectively. Kammerer et al. (2004) quantified the total amount of ACY in 14 wine
grape varieties ranged from 11.47 to 29.82 mg/g DM by using HPLC.
The total flavanol content (TFC) and proanthocyanidins (PAC) differed
significantly among WGP varieties (Table 3.5). The TFC values in this study
represented the amount of monomeric flavanols (free or terminal of PAC) in the
aqueous solution whist the PAC values indicated the amount of oligomeric and
polymeric flavan-3–ols which were linked by C – C bonds (Muller-Harvey and
McAllan, 1992), were determined by the acid butanol assay. Merlot, Muller Thurgau
and Cabernet Sauvignon were of the highest content of TFC, followed by Pinot Noir
and Morio Muscat (p <0.05) (Table 3.5). Likewise, Merlot possessed the highest PAC,
followed by Muller Thurgau, Cabernet Sauvignon, Pinot Noir and Morio Muscat (p
<0.05). Although TPC for WWGP were lower than those for RWGP, TFC and PAC
values did not show significant difference between WWGP and RWGP varieties
(p>0.05) (Table 3.5). Furthermore, neither linear correlation between RSA and TFC
(R=0.653) nor between RSA and PAC (R=0.667) was observed (Figure 3.2), which
was consistent with the previous study by Bozan et al. (2008).
Overall, WGP had high TPC values comparing with other fruit byproducts.
Among the five WGP varieties evaluated in this study, Merlot ranked the first in all
phenolic compounds. Muller Thurgau also displayed relatively high values of TFC
and PAC.
68
Conclusion
This study was the first one that successfully characterized the chemical
composition of polyphenols and dietary fiber of WGP skins from the Pacific
Northwest. Results provided the baseline data for developing innovative utilizations of
the WGP skins. Overall, the RWGP skins had high contents of TPC, RSA, ACY, TFC
and PAC, making them excellent candidates for food applications such as food
additives with high antioxidant capacity and food coloring ingredient. They are also
good sources of dietary fiber with high contents of Klason lignin, cellulose, and
hemicellulose, hence are of great potentials of being environmental-friendly
supporting materials. The distinctively high amount of soluble sugar in the WWGP
skins may enable them to form innovative biodegradable packaging materials with
excellent flexibility. However, further study is necessary to improve WGP preparation
procedures for obtaining bright color, appreciative aroma, more soluble fractions and
nutrient compounds.
Acknowledge
The author would like to thank Dr. Mark Daeschel and Dr. James Osborn for
donating wine grape pomace, Dr. Seth Cohen for kindly providing wine grape skin
condensed tannins, Mr. Jeff Goby for helping the analysis of neutral sugars by HPLC,
and Ms. Jooyeoun Jung for analyzing resistant protein.
69
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74
CHAPTER 4
Physicochemical, Nutritional and Antimicrobial Properties of Wine Grape (cv.
Merlot) Pomace Extract Based Films
Qian Deng and Yanyun Zhao*
Department of Food Science and Technology, 100 Wiegand Hall,
Oregon State University, Corvallis, OR 97331, USA
*corresponding author: Email: [email protected]
Accepted by Journal of Food Science
525 W. Van Buren, Suite 1000, Chicago, IL 60607
75
Abstract
Wine grape (cv. Merlot) pomace (WGP) extract based films were studied in
terms of their physicochemical, mechanical, water barrier, nutritional and antibacterial
properties. Pomace extract (PE) was obtained by hot water extraction and had a total
soluble solid of 3.6% and pH 3.65. Plant based polysaccharides, low methxyl pectin
(LMP, 0.75% w/w), sodium alginate (SA, 0.3% w/w), or Ticafilm® (TF, 2% w/w),
was added into PE for film formation, respectively. Elongation at break and tensile
strength were 23% and 4.04 MPa for TF-PE film, 25% and 1.12 MPa for SA-PE film,
and 9.89% and 1.56 MPa for LMP-PE film. Water vapor permeability of LMP-PE and
SA-PE films was 63 and 60 g mm m-2
d-1
kPa, respectively, lower than that of TF-PE
film (70 g mm m-2
d-1
kPa) (p<0.05). LMP-PE film had higher water solubility,
indicated by the haze percentage of water after 24 h of film immersion (52.8%) than
that of TF-PE (25.7%) and SA-PE (15.9%) films, and also had higher amount of
released phenolics (96.6%) than that of TF-PE (93.8%) and SA-PE (80.5%) films. PE
films showed antibacterial activity against both E. coli and L. innocua, in which
approximate 5 log reductions in E. coli and 1.7-3.0 log reductions in L. innocua were
observed at the end of 24 h incubation test compared with control. This study
demonstrated the possibility of utilizing WGP extracts as natural, antimicrobial, and
antioxidant promoting film forming material for various food applications.
Key words: wine grape pomace extract, edible films, solubility, total phenolic
compounds, physicochemical and antibacterial property
76
Introduction
The increasing demand for environmentally friendly packages forced the
researchers to conduct study on biodegradable and edible packaging materials. Some
recently developed edible films have shown their competitive mechanical and mass
transfer properties respect to the synthetic ones. In addition, the capability of carrying
functional substances, such as antioxidant and antimicrobial agents has further
enhanced their functionality to extent shelf-life of packaged food products (Han and
Gennadios, 2005).
Fruit and fruit byproducts have attracted great interests as film forming
components because of their rich contents in celluloses, hemicelluloses, pectin,
pigments, flavors, and bioactive compounds, such as polyphenolics with demonstrated
antioxidant and antimicrobial properties. Wine grape pomace (WGP), the by-residual
from wine processing composed of a mass of skins, seeds, and stems, is a rich source
of dietary fibers, and possesses significant amount of polyphenols (Katalinić et al.,
2010). WGP extracts may be utilized as film forming materials since the extracts
contain pectin, celluloses, and sugars (Deng et al., 2011), the essential compounds for
film formation. The natural pigments, flavors, and polyphenols from WGP extracts
would provide additional benefits to its applications.
Different approaches may be employed when forming films using fruit or fruit
byproducts. Fruit purees, such as mango, apple, and peach puree contain high soluble
polysaccharides, thus can be directly utilized as basic film forming material with the
aid of plasticizer to improve film functionality (McHugh et al., 1996; McHugh and
Senesi, 2000; Azerodo et al., 2009). When using fruit byproducts, such as pomace
with relative low soluble polysaccharides, polysaccharides and other functional
compounds from pomace are first extracted using water or other food grade solvents.
The extracts are then directly incorporated into film forming solutions, freeze-dried or
concentrated for later use. For this application, a small amount of film forming
material (polysaccharide or protein) is usually required in order to obtaining films with
desirable mechanical and barrier properties (Mayachiew and Devahastin, 2010;
77
Corrales et al., 2009; Hayashi et al., 2006). We have previously developed cranberry
pomace based edible films by adding pectin and glycerol into the pomace extracts
(Park and Zhao, 2006). The resulting films had compatible mechanical strength and
water vapor permeability as other edible films, such as whey protein isolate based
films (McHugh and Krochta, 1994; Shaw et al., 2002), plus an attractive bright red
color and the distinctive cranberry flavor.
Different polysaccharides may be incorporated into PE to assist the film
formation. Low methoxyl pectin (LMP), composed of galacturonic acid backbone
chains with less than 50% of esterified carboxyl groups, is one of the non-starch
polysaccharide film forming materials. It works well with other polysaccharides, such
as starch and chitosan (Mariniello et al., 2003; Coffin et al., 1993; Fishman and others
1994) and plasticizers as polyvinyl alcohol, sorbitol, or glycerol (Fishman and Coffin,
1998; Park and Zhao, 2006) to obtain films with excellent mechanical properties.
Sodium alginate (SA), widely used in food industry (Mancini et al., 2002), is also used
as film forming material with glycerol to form films with good tensile strength and
elongation (Wang et al., 2007). Cellulose gums, having a structure of D-glucose units
and partial carboxymethylation of the hydroxyl groups, is water soluble and
compatible with other film forming materials, such as starch, proteins, alginate, and
pullulan (Zecher and Gerrish, 1997; Tong et al., 2008). Carrageenan from seaweed has
also been widely utilized as gelling agent and film forming material (Thomas, 1997).
In this study, three commercial polysaccharides, LMP, SA, and Ticafilm® (mixture of
cellulose gum, SA, and carrageenan, TIC Gum, Belcamp, MD, USA) were
incorporated into WGP extracts for forming films. All these materials are plant based,
food-graded, and colorless with good film forming properties.
The objectives of this study were to investigate the feasibility of utilizing WGP
water extracts with the incorporation of a small amount of commercial
polysaccharides (LMP, SA and Ticafilm®) as film forming materials, and to evaluate
the physicochemical, antioxidant, and antimicrobial properties of the films. Based on
our previous success on developing cranberry pomace extracts based edible films
78
(Park and Zhao, 2006) and identified high amount of bioactive compounds in wine
grape pomace (Deng et al., 2011), we hypothesized that WGP water extract can be
used as a base to develop edible films with antimicrobial and antioxidant activities,
and with similar mechanical and water barrier properties respect to the widely reported
edible films, with the aid of additional polysaccharides. Based on our best knowledge,
the polysaccharide based film literature has virtually no reports on developing edible
films using WGP extracts as film forming material.
Materials and Methods
Materials
Fresh red wine grape pomace cv. Merlot (Vitis vinifera) was donated by the
Oregon State University Research Winery (Corvallis, OR, USA) in the fall of 2009
and immediately stored at -24 oC till processing. Three types of commercial
polysaccharides were provided by TIC Gum (Belcamp, MD, USA), including LM 32,
a low methoxyl pectin (LMP) with a degree of esterification 17% to 25%; TICA-
algin® HG 400, sodium alginate (SA) of medium viscosity; and Ticafilm® (TM), a
mixture of sodium alginate, carrageenan, and cellulose gum. Glycerol from Fisher
Scientific Inc. (Fair Lawn, NJ, USA) was employed as a plasticizer.
Folin-Ciocalteu (FC) reagent (2N) (Sigma Chemical Co., MO, USA) was used
to determine total phenolic content. Plate count agar (PCA), tryptic soy agar (TSA),
tryptic soy broth (TSB), and brain heart infusion broth (BHI) were purchased from
Becton Dickinson and Co. (Sparks, MD, USA). Bacterial cultures, Escherichia coli
ATCC 25922 (E. coli) and Listeria innocua ATCC 51742 (L. innocua) were
purchased from American Type Culture Collection (ATCC) (Manassas, VA, USA).
Preparation of red wine grape pomace extracts
Only the skins of red wine grape pomace were used for the extraction. The
skins were separated manually from the seeds and stems, dried at 70 oC and 10% RH
for 24 h (T10RS, Tenney Environmental, Williamsport, PA, USA), and then milled to
pass a 20 mesh (Thomas Scientific, Swedesboro, NJ, USA) as described by Park et al.
79
(2009). The dried pomace powders were packed and sealed in Ziploc® storage bags
(S.C. Johnson & Son, Inc., Racine, WI, USA) and stored at -24 oC until utilization.
Pomace extract (PE) was prepared according to the procedures by Park and
Zhao (2006) with some modifications (Table 4.1). Briefly, pomace powders were
homogenized with 75 oC preheated deionized (DI) water at a ratio of 1: 4 (w/w) at
4,000 rpm (PT 10-35, Kinematica, Littau, Switzerland) for 10 min for enhancing the
release of soluble carbohydrates, polyphenolics, and pigments into the solution. The
mixture was then placed into a 75 oC water bath (Precision, Winchester, VA, USA) for
30 min following by squeezing out water soluble extract through 4 layers of cheese
cloths. The obtained solution was centrifuged at 10,000 g and filtrated through
Whatman 1 filter paper (Whatman Inc., Piscataway, NJ, USA) for three times until
crystalline salts (Jackson, 2000) were no longer observed. The filtrate was the pomace
extract used for film formation.
Table 4.1 Formulations of wine grape pomace (WGP) extract based film forming
solutions (FFS)
Pomace extract
(PE) WGP powder: hot water = 1:4
Film type* PE
(w/w FFS, %)
Polysaccharides (w/w
FFS, %)
Plasticizer
(w/w FFS, %)
LMP-PE 99.0 0.75 0.25
SA-PE 99.7 0.30 0
TF-PE 98.0 2.00 0 *
LMP= low methoxyl pectin; SA = sodium alginate; TF = Ticafilm® (mixture of
sodium alginate, carrageenan and cellulose gum).
Film formation
Pomace water extract alone does not contain enough polysaccharides to form
films with desirable mechanical and barrier properties, thereby additional
polysaccharides, LMP, SA and Ticafilm®, were incorporated in the film forming
solutions in order to evaluate their compatibility with PE. They were all plant based
and food graded non-starch polysaccharides and are commercially available as film
80
forming materials. In addition, glycerol was added as a plasticizer in some film
formula to improve film flexibility.
Preliminary studies allowed finding out the best ratio of polysaccharide and PE
as edible film. Our previous study (Park and Zhao, 2006) has reported that the films
based on cranberry pomace extract, 0.75% LMP, and 0.25% glycerol (w/w FFS) have
functional properties similar to other polysaccharide based films.
This formulation was applied for developing wine grape pomace extract based
LMP-PE film. For SA films, the most appropriate concentration was 0.3% SA (w/w
FFS) for forming SA-PE film with easy film casting and desirable film performance.
Our preliminary tests identified that 2% Ticafilm® (w/w FFS) is necessary to form
TF-PE films. Table 4.1 summarizes the final formulations of the film forming
solutions.
For preparing the FFSs, accurately weighed amount of PE was first warmed up
to 35-40 oC in a water bath, and then 0.75% LMP, 0.3% SA, or 2.0% Ticafilm® was
slowly added with constant stirring. For LMP-PE FFS, 0.25% (w/w FFS) glycerol was
also added when LMP was completely dissolved in the PE solution. The FFSs were
stirred at room temperature for 1 h and further homogenized at 2,000 rpm for 60 s for
preventing the lump formation. Finally, the FFSs were degassed under water aspirator
vacuum until no bubble was observed. The pH values of FFSs and PE were measured
before casting films.
Total soluble solid content (TSS, %) of FFS was a critical factor for obtaining
uniform film thickness, and was measured by a digital refractometer (Brix RA-250 HE,
Kyoto Electronics Manufacturing Co. Ltd., Kyoto, Japan). A calculated amount (Eq.
4.1) of each degassed FFS was cast onto a Teflon-coated glass plate with an area of
260 mm×260 mm.
TSS%LMP-PE × WLMP-PE = TSS%SA-PE × WSA-PE = TSS%TF-PE × WTF-PE (4.1)
where W was the weight of FFS (g). The FFSs were poured onto the plates and
dried at ambient conditions (24±2 oC and 40% ± 5% RH) for 36-48 h. Dried films
were then peeled and conditioned inside a cabinet assembled by our lab at 25 oC and
81
47 ± 2% RH (provided by saturated sodium bromide) for at least 24 h before any
testing. The FFSs and the films were performed in triplicate.
Determination of film color, water activity, and moisture content
Color of each individual film was measured at 3 random locations using a
colorimeter (Lab-Scan II, HunterLab, Inc., Reston, VA, USA) which was standardized
by a black and a white color plate (XCIE = 78.25, YCIE =82.85 and ZCIE = 85.83) with
illuminant D65, 0/45 geometry, and 10o observer. CIE L*, a*, b* values were recorded,
and average values were reported for each film replication (Park and Zhao, 2006).
Water activity (αw) of the films was measured by using the AquaLab water
activity meter (Decagon AquaLab Inc., Pullman, WA, USA). The instrument was pre-
standardized using 8.57 M LiCl (αw = 0.500). Moisture content was determined by
drying films at 75 oC in forced air convection oven (Precision Scientific, Inc., Chicago,
IL, USA) for 24 h, and expressed as the percentage of weight loss after drying.
Mechanical properties
Six strips (25 mm x 86 mm) of each film type at each replication were used for
the measurement of film thickness, film density and mechanical properties. The film
thickness was measured at 5 randomly selected spots of each strip, and the average
thickness was reported. Film density was obtained by the weight of each film strip
divided by the volume of each strip, and the average of film density was expressed as
gram per milliliter. A texture analyzer (TA XT2i, Texture Technologies Corp.,
Scarsdale, NY, USA) was utilized to determine mechanical properties by using
modified ASTM D882 standard (ASTM Intl, 2001; Park and Zhao, 2006). Briefly, a
film strip was mounted on the sample grips (TA96) between which the distance was
80 mm with the crosshead speed of 0.4 mm/s. The maximum loaded force (N) and
elongation of the strip ( L) was recorded. The tensile strength (TS) was reported as
maximum loaded force (N) divided by the area of cross section (mm2) and the
elongation at break (EL %) was expressed as L divided by the initial length of tested
strip and multiplied by 100%.
82
Water vapor permeability
Water vapor permeability (WVP) of the films was measured by using the cup
method according to ASTM E 96 (ASTM Intl. 2000) at 25 oC and 100/50% RH
gradient. Eleven mL of DI water was added into a Plexiglas test cup with inner depth
and diameter of 15 mm and 57 mm, respectively. A film specimen (75 mm × 75 mm)
was sealed on the top of the cup by vacuum grease and the distance between film and
water surface was 10.7 mm. Test cup assemblies were placed in the same temperature
and humidity controlled chamber conditioned at 25 °C and 50% RH. Each cup
assembly was weighted every one hour for 6 h and the weight loss versus time was
plotted linearly. WVP (g mm m-2
d-1
kPa-1
) was calculated by following the WVP
correction method (Gennadios et al., 1994; Park and Zhao, 2006). WVP was
determined twice for each film type at each replication.
Microstructures
Microstructure of the films was evaluated using a Nikon Eclipse E400
microscope (Nikon Co., Tokyo, Japan) equipped with an extended digital camera (Q
imaging, Surrey, BC, Canada). The surfaces of films were observed at a magnification
of 40X.
Total phenolics content (TPC) of FFSs and phenolics release from films into
aqueous solution
To evaluate TPC of FFSs, 1 g of FFS was diluted to 10 mL with DI water in a
10 mL volumetric flask. The TPC of FFS for each film type was calculated by
multiplying weight of FFS per casted film (260 mm x260 mm) and TPC per gram of
FFS solution. The TPC released from the films was monitored by placing 1 g of film
specimen into 100 mL DI water with constantly shaking in an environmental shaker
(100 rpm) based on the method by Mayachiew and Devahastin (2010) with some
modifications. A 2 mL of supernatant was obtained at 10 different sampling times
between 0 to 24 h, and then stored at -20 oC until TPC analysis. The total released
TPC was calculated as the released TPC accumulated after 24 h and expressed as mg
83
gallic acid equivalent per film (260 mm x 260 mm). TPC release test was carried out
twice for each film type at each replication.
TPC was quantified by Folin-Ciocalteu (FC) assay (Singleton and Rossi, 1965).
Briefly, 0.5 mL 2N FC reagent, 0.5 mL sample solution, and 7.5 mL DI water were
mixed in a test tube and settled at room temperature for 10 min before 3 mL of 20%
CaCO3 was added and reacted at 40 oC for 20 min. The sample was read at 765 nm
using a spectrophotometer (UV160U, Shimadzu, Kyoto, Japan).
Water solubility
One gram of the PE film specimen was placed into 100 mL DI water as
described above. Water solubility of the films was evaluated by monitoring the
changes of turbidity in the aqueous solution using a ColorQuest Sphere
spectrophotometer (ColorQuest HunterLab, HunterLab, Inc., Reston, VA, USA) (0/45
geometry, 10o observer, illuminant D65). The haze of solution was recorded at 0.5, 2, 4,
8, 12, and 24 h by placing the supernatant into 10 mm length quartz cell (Ngo and
Zhao, 2009). The experiment was carried out once for each film type at each
replication.
Antibacterial activity against Escherichia coli and Listeria innocua
To investigate the antibacterial activity of PE films against Gram-negative and
Gram-positive bacteria, bacterial strains of Escherichia coli ATCC 25922 and Listeria
innocua ATCC 51742, a modified method by Duan et al. (2008) was applied. A 0.35 g
of PE film specimen was placed in a Petri dish (85 mm diameter) which contained 10
mL of bacterial culture with an initial cell concentration at approximately 105
CFU/mL. Bacterial culture without film specimen was used as control. The Petri
dishes were shaken at 100 rpm at room temperature, and the samples were taken at 0,
4, 8, and 24 h. The samples were diluted with phosphate-buffered saline (PBS) and
plated on TSA or BHI agar for E. coli and L. innocua enumeration, respectively.
Plates were incubated for 24 h at 35 ◦C for E. coli and at 30 ◦C for L. innocua before
84
counting the number of colonies. For each bacterial strain, each film type was tested
on triplicate.
Experimental design and statistical analysis
Three film types (SA-PE, LMP-PE and TF-PE) were prepared independently
on triplicate using a completely randomized design (CRD). For film thickness, tensile
strength, elongation, and density, six pieces of each film type were measured for each
replication. For color, three measurements were performed for each film type. For the
TPC releasing test and WVP, two measurements were conducted for each film type at
each replication. For TSS, pH, water activity, moisture content, and TPC of FFS, one
measurement was conducted for each film type at each replication. Antibacterial
activity was conducted on triplicate for each bacterial strain. Results were expressed as
mean ± SD. One way ANOVA (Tukey-Kramer multi-comparison) was used to test the
differences among three film types using SAS (SAS Inc., Cary, NC, USA) (p<0.05).
Results and Discussion
Total soluble solid (TSS) and pH values of PE and FFS
Wine grape pomace extract had a TSS of 3.6%, the addition of TF or LMP into
PE significantly increased TSS of FFSs (Table 4.2), in which the TSS of TF-PE and
LMP-PE FFSs was increased by about 47% and 21%, respectively (p<0.05) and the
FFSs were visibly more viscous than that of PE alone. Adding 0.3% SA did not
change the TSS of SA-PE FFS (p>0.05). These results were similar to the report by
Park and Zhao in which adding same amount of LMP or HMP (high methoxyl pectin)
into cranberry pomace extract increased the TSS to a similar level (Park and Zhao,
2006). Park and Zhao (2006) indicated that the soluble solid ratio of PE and added
polysaccharides in FFS is critical for film formation and resulting film functionality
due to the characteristics of the different polysaccharides. Table 4.2 shows the
formulations and ratios of PE, polysaccharide and glycerol.
85
Table 4.2 Total soluble solids (TSS), pH and casting weight of film forming
solutions (FFS)*
FFSs+ TSS (%) pH Casting
weight
Ratio of soluble solid in PE,
added polysaccharide and
glycerol
PE 3.60±0.00c
3.65±0.02b
- -
LMP-PE 4.37±0.06b
3.65±0.06b
226.59±3.02b
PE:LMP:Glycerol =4.8:1:0.3
SA-PE 3.77±0.06c
3.79±0.06ab
261.65±2.31a
PE:SA:Glycerol = 12.0:1:0
TF-PE 5.30±0.10a
4.11±0.21a
188.39±3.56c
PE:TF:Glycerol =1.8:1:0 * Values within the same column with the different superscript meant significant
difference among the films (p<0.05), n=3. +
LMP = low methoxyl pectin; SA = sodium alginate; TF = Ticafilm® (mixture of
sodium alginate, carrageenan and cellulose gum).
Different polysaccharides have different gel formation mechanisms. SA and
LMP require divalent cations, such as Ca2+
, carrageenan needs mono- or divalent
cations, while multivalent cations, such as Fe 3+
is necessary for cellulose gum as the
crosslinking agents to link the adjacent chains to form gels (Onsøyen, 1997; May,
1997; Thomas, 1997; Zecher and Gerrish, 1997). Based on our previous study, wine
grape pomace (cv. Merlot) contains different types of crosslinking agents, such as
minerals, proteins, organic acids, and phenolic acids, at least 22% on dry matter
(except organic acids) (Deng et al., 2011). Moreover, some of those fractions were
water soluble compounds. Therefore, there were sufficient crosslinking agents in the
PE to assist the film formation without the need of adding other additional
crosslinking agents.
The pH of the PE was 3.65. About 90% of organic acids in grapes and wines
were malic and tartaric acid (Jackson, 2000). Therefore, it could be concluded that
those two organic acids were also dominated in the wine grape PE, thus resulted in the
high acidity of wine grape PE. Adding TF and SA increased the pH of FFSs to 4.11
and 3.79, respectively, while the pH of LMP-PE FFS was similar to that of PE. The
pH value of wine grape PE was higher than that of cranberry pomace extract (pomace:
water= 1:5, pH=2.86) reported by Park and Zhao (2006).
86
Microstructures
Figure 4.1 shows the surface microstructures of the films under the 40×
magnification. Globules were observed on the surfaces of all three types of films, in
which the TF-PE film formed the largest globules followed by LMP-PE and SA-PE
films. In the TF-PE films, particles from the film forming materials were un-uniformly
dispersed in the film matrix, reflected by the lower density (Table 4.3) and higher
water vapor permeability (Figure 4.2) of TF-PE films as reported and discussed in the
later sections. Compared with TF-PE film, the LMP-PE and SA-PE films were more
compact, dense and uniform, and had similar surface structure. The larger globule
formation in the TF-PE films might be attributed by the remarkably higher amount of
Ticafilm® material employed in the FFS resulting in decreased homogeneity of TF-PE
film, as similarly observed by Kayserilioğlu et al. (2003) that the increase of xylan in
wheat gluten films enlarged the globular formation and reduced the homogeneity of
the films.
87
C
A B
Figure 4.1 Surface microstructures of wine
grape pomace extract based films viewed at
magnification 40×; (a) TF-PE; (b) LMP-PE;
(c) SA-PE. LMP=low methoxyl pectin;
SA=sodium alginate; TF=Ticafilm® (mixture
of sodium alginate, carrageenan and cellulose
gum).
88
Table 4.3 Moisture content, water activity, density, mechanical properties and color of wine grape pomace extract
based films
Film+ Weight
(g)
Moisture
content
(%)
Water activity Density
(g/mL) TS (MPa) EL (%) L* a* b*
LMP-PE 12.0±0.6a 20.5±1.0
a 0.470±0.026
a 1.46±0.06
a 1.56±0.39
b 9.89±1.56
b 18.17±1.86
a 6.97±1.00
a 9.70±2.32
a
SA-PE 11.5±0.7a 15.5±2.3
b 0.484±0.029a 1.53±0.02
a 1.12±0.18b 25.07±2.94
a 18.97±0.79
a 6.66±0.47
a 8.83±0.92
a
TF-PE 11.5±0.7a 11.7±0. 4
c 0.470±0.035
a 1.29±0.09
b 4.04±0.29
a 23.05±2.82
a 21.40±1.43
a 7.07±0.58
a 9.80±1.25
a
a Values within the same columns with the different superscript meant significant difference among the films (p<0.05).
+ LMP = low methoxyl pectin; SA = sodium alginate;
TF = Ticafilm® (mixture of sodium alginate, carrageenan and
cellulose gum)
89
Physicochemical properties
Depending on the film formulation, it took 36 to 48 h to dry the films at room
condition, of which the TF-PE films dried the fastest (36 h), probably due to the
lowest amount of casting solutions used, followed by LMP-PE and SA-PE films.
Moisture contents (MC) of the films differed significantly (p<0.05), 20%, 16%, and 12%
for LMP-PE, SA-PE, and TF-PE films, respectively (Table 4.3). LMP-PE film
possessed the highest MC, probably due to the addition of glycerol (0.25% w/w) that
is known for its water attracting and holding capacity. There was no difference in
water activity (αw) among the different films, 0.470 to 0.484 (Table 4.3). The low αw
values below 0.60 proved that the films developed in this study were stable and
capable of retarding microbial proliferation under room conditions (Fontana and
Campbell 2004). TF-PE film had the lowest density compared with other two films,
which agreed with the observed loose surface microstructures of TF-PE films (Figure
4.1).
Color of the three types of films was not different (p>0.05) (Table 4.3). L*
values (lightness) were in a range of 18.2 to 21.4, a* values (redness) of 6.7 to 7.1, and
b* values (yellowness) of 8.8 to 9.8. Anthocyanins in the PE contributed to the color
of the films. Anthocyanins are pH sensitive, showing different colors depending on the
pH values. In this study, pH values of the FFSs were in the range of 3.65 to 4.11
(Table 4.2) within which the FFSs were in similarly red color. After drying, films
retained visually red. The polysaccharides (LMP, SA, and TF) and glycerol added into
FFSs were colorless, thus no impact on the color of the films. This observation was
consistent with our previous findings on the pectin-cranberry pomace extract based
films (Park and Zhao, 2006).
Mechanical properties
Tensile strength (TS) were significantly different among the three film
formulations (p<0.05) (Table 4.3), in which TS of TF-PE film was 4.0 MPa, about 2.6
times higher than those of other two films. Elongation at break (EL%) of SA-PE and
90
TF-PE films were 153% and 133% that of LMP-PE film. The type and concentration
of polysaccharides used for forming films significantly affected film mechanical
properties: the SA-PE film was the mostly elastic, but the weakest in strength, while
the LMP-PE film was weak in both elasticity and tensile strength. On the other hand,
TF-PE film had the best mechanical properties, strongest and most flexible. Ticafilm®,
a mixture of cellulose gum, carrageenan, and sodium alginate (portion for each
ingredient is unavailable), is claimed to be of superior film forming properties. As
indicated before, our preliminary study found that a high amount of Ticafilm® (2%,
w/w FFS) was necessary to carry the soluble solids from PE for forming the TF-PE
film with smooth surface and sufficient tensile strength. With the increased amount of
Ticafilm® material, TS was largely increased without reducing EL%. This result
agreed with the report by Azeredo et al. (2009) in which increased loading of cellulose
nanofibers into mango puree based edible films strengthened TS without diminished
the elastic properties unless the loading cellulose nanofibers amount was over the
optimum amount.
PE contains cellulose, hemicellulose, pectic polysaccharides, minerals, proteins,
lipids, and organic acids (Deng et al., 2011). The polysaccharides (cellulose gum,
carrageenan, sodium alginate, and low methoxyl pectin) added into PE have different
functional groups, including hydroxyl, sulphate (specific to carrageenan), carboxyl,
ester, and acid groups. Various interactions might occur during the film forming
process. Unfortunately, it was impossible to conclude the effects of these interactions
on the mechanical properties of the films since the specific proportion of each
compound in the FFS was unknown.
Compared with other fruit byproduct based edible films (Table 4.4), TF-PE
film could be considered as strong and flexible, SA-PE film was soft and flexible, but
LMP-PE film was not competitive with other films in terms of the mechanical
properties.
91
Table 4.4 Bibliographical values of mechanical properties and water barrier properties of fruit pomace base edible films
Film forming material TS
(MPa)
EL
(%)
WVP
(g mm m-2
d-1
kPa-1
)
Condition
for WVP Reference
Cranberry pomace extract (1.38% TSS)
incorporating with 0.50-0.75% of pectin (LMP
and HMP) and 0.25% of plasticizer (sorbitol or
glycerol)
1.0-8.1 12.9-47.7 70-80
25 oC;
100%/50%
RH
Park and Zhao
(2006)
Spinach extract (0-1.05% TSS) and wine grape
pomace extract (cv. Merlot) (0-8.16% TSS)
incorporating with cassava starch (5%), sucrose
(0.7%) and inverted sugar (1.4%)
1.8-4.2 65-217 1406.0-8804.75 75%/0%
RH
Hayashi and others
(2006)
26% of apple puree (38% TSS), 70.5% of 3%
LMP solution, 0.25% of ascorbic acid and citric
acid, 3% of glycerol and 0-1.5% of carvacrol
(w/w)
1.25-
1.93 38.1-50.3 91.4-121.2
25±1 oC;
77.4-
80.4%/0
RH
Du and others
(2008, a)
26% of apple puree (38% TSS), 71.5% of 2%
alginate solution, 1.0% of 1% N-acetylcysteine
and 1.5% glycerol and 0-0.5% essential oils
2.47-
2.90 51.1-58.3 104.9-126.0
25±1 oC;
63.5-67.1%
/0 RH
Rojas-Graü and
others (2007)
0-36 g of cellulose nanofibers and 100 g of
mango puree solution (27.5% TSS)
4.09-
8.76 31.5-43.3 40.1-63.8 N/A
Azeredo and others
(2009)
50.0-90.0% of PVA (10% TSS), 10.0-50.0% of
natural fibers (orange byproducts, apple pomace
or sugar cane bagasse) and various amounts of
glycerol, urea, starch, hexamethoxylmelamine
and citric acid
2-52 5.0-20.0 N/A N/A Chiellini and others
(2001)
92
Table 4.4 (continued)
Film forming material TS
(MPa)
EL
(%)
WVP
(g mm m-2
d-1
kPa-1
)
Condition
for WVP Reference
Mango puree (19% TSS) 1.2 18.5 213.2 27
oC,
50%/0 RH
Sothornvit and
Rodsamran (2008)
Small amount of cavacrol and tomato paste which
was formed by mixing 30% of tomato puree (31%
TSS) and 70% of 3% high methoxyl pectin
solution together
8.9-14.8 6.0-11.6 50.64-64.32
25±1 oC;
81.5-
85.1%/0
RH
Du and others
(2008, b)
4% of dry banana starch (native or oxidized), 2%
of glycerol and 0.2% of sunflower oil 3.5-4.0 12.5-35.0 17.3-121.0
25 oC ;
100%/57%
RH
Zamudio-Flores and
others (2006)
93
Water vapor permeability
Thickness of the films directly influences WVP values. The thickness of TF-
PE film was about 160 μm, about 20 μm and 30 μm higher than that of MP-PE and
SA-PE films, respectively (Figure 4.1). WVP of TF-PE, LMP-PE and SA-PE films
were about 70, 63, and 60 g mm m-2
d-1
kPa at 25 oC and 100/50% RH, respectively,
with TF-PE film had significantly higher WVP value than that of other films (p<0.05)
(Figure 4.2). All polysaccharides evaluated in this study are hydrophilic materials with
high water holding capacities, thus poor water barrier properties when forming films.
The larger thickness of TF-PE film may contribute to its high WVP value compared
with the other two films as previous study indicated that the thicker the hydrophilic
edible film, the higher the WVP values (McHugh et al., 1993). Also, the less
compacted structure of TF-PE film might reduce its moisture barrier ability (Figure
4.1).
Figure 4.2 Water vapor permeability (g mm m
-2 d
-1 kPa
-1) of wine grape pomace
extract based films corresponding to film thickness (μm). Different letters
indicated the significant difference at p<0.05. LMP=low methoxyl pectin;
SA=sodium alginate; TF=Ticafilm® (mixture of sodium alginate, carrageenan
and cellulose gum).
0
20
40
60
80
100
120
140
160
180
LMP-PE SA-PE TF-PE
thickness (um) WVP (g mm per m^2 d kPa)
a
a
b
b
b
b
94
Compared with the WVP values in other fruit (puree) and fruit byproduct
based films as shown in Table 4.4, WVPs of the films from this study were relatively
low. In general, fruit and fruit byproduct base edible films displayed poor moisture
barrier ability owing to the hydrophilic nature of the materials unless hydrophobic
materials were incorporated. For instant, WVP of apple puree based edible films
ranged from 91.4-126.0 g mm m-2
d-1
kPa (Du et al., 2008a; Rojas-Graü et al., 2007),
and mango puree base edible films with or without other film forming materials were
40.1-63.8 (Azeredo et al., 2009) or 213.2 g mm m-2
d-1
kPa (Sothornvit and
Rodsamran, 2008). Therefore, the moisture barrier properties of wine grape PE based
films from this study were promising (Figure 4.2).
Water solubility
Distinct differences of film solubility were observed among the three types of
films (Figure 4.3). LMP-PE film was highly water soluble with the haze percentage
value of its aqueous solution reached to about 46% at the end of 12 h, and the film
specimens were visually disintegrated. However, the solubility significantly slowed
down during the last 12 h. The haze percentage value at the end of 24 h was about 52%
(Figure 4.3). Adversely, the haze percentage values of SA-PE and TF-PE films
maintained stable within the first 12 h immersion in water (~7% at 12 h), and then
increased to 17% and 26%, respectively at the end of 24 h, at which the more turbid
aqueous solutions were observed. Compared with LMP-PE film, TF-PE and SA-PE
films retained their integrity after immersion into water for 24 h.
95
Figure 4.3 Solubility of wine grape pomace extract based films in aqueous
solution. The results are the mean of triplicates with standard deviations. LMP=
low methoxyl pectin; SA=sodium alginate; TF=Ticafilm® (mixture of sodium
alginate, carrageenan and cellulose gum).
It has been well recognized that film solubility largely depends on the amount
of crosslinking materials participating in the film forming process (Jin et al., 2004;
Cao et al., 2007). In general, the more the crosslinking materials, the lower the
solubility of the films. Wine grape PE provided several types of crosslinking materials,
such as minerals (Ca2+
, Mg2+
, and Fe3+
) and acids (organic acids, amino acids, and
phenolic acids) (Pavlath et al., 1999; Cao et al., 2007). In this study, SA-PE film had
the highest ratio of total solids from PE, followed by LMP-PE and then TF-PE film
(Table 4.2). The high water solubility in LMP-PE film might attribute to its high
moisture content and the added glycerol which is highly water soluble. The different
film forming properties of LMP (0.75% w/w FFS) and Ticafilm® (2% w/w FFS)
might also impact the water soluble property of the films.
Total phenolics content (TPC) of FFSs and TPC release from films
The TPC values significantly differed among the three FFSs (p<0.05), in the
order of SA-PE (167.8 mg GAE/g FFS)> LMP-PE (148.5 mg GAE/g FFS) >TF-PE
(111.5 mg GAE/g FFS) (Figure 4.4). Unlikely, the amount of TPC released from the
films into distilled water at the end of 24 h in room temperature followed different
orders, in which the largest amount was from LMP-PE film (144.1 mg GAE/film),
0
10
20
30
40
50
60
70
0 4 8 12 16 20 24
Ha
ze, %
Time (hr)
LMP-PE SA-PE TF-PE
96
followed by SA-PE film (134.3 mg GAE/film) and TF-PE film (104.7 mg GAE/film)
(Figure 4.4). About 96.6% TPC was released from LMP-PE film while 93.8% was
released from TF-PE film and 80.5% from SA-PE film. Different interaction
mechanisms between phenolic compounds and polysaccharides might attribute to the
diverse release characterization of TPC from different films. First, the formation of
polysaccharide-phenol complex might be due to the interaction of hydrogen bonds of
phenolic hydroxyl groups with the oxygen atoms of the crosslinking ether bonds of
sugars by which the phenolic compounds are entrapped into the polysaccharide pores
(Pinelo et al., 2006). Secondly, the form of hydrophobic regions of polysaccharides
might encapsulate phenolic acids inside the hydrophobic regions thereby caused the
aggregation of phenolic compounds (Pinelo et al., 2006). Further, film solubility also
correlated with phenolic compound released from hydrophilic films (Mayachiew and
Devahastin, 2010). LMP-PE film with the highest film solubility had the highest
released TPC while SA-PE films with the lowest water solubility had the lowest
amount of released TPC.
Figure 4.4 Total phenolics content (TPC) in film forming solutions (FFS) and
amount of TPC released from films at the end of 24 h water immersion test. The
different letters indicated the significant differences among the films at p<0.05.
LMP=low methoxyl pectin; SA=sodium alginate; TF=Ticafilm® (mixture of
sodium alginate, carrageenan and cellulose gum).
0
20
40
60
80
100
120
140
160
180
200
220
TPC of the FFS TPC of film
TP
C (m
g G
AE
/fil
m)
TF-PE LMP-PE SA-PE
a
b
dc
bc
d
Released TPC of film
97
The release kinetics of phenolic compounds from the films is shown in Figure
4.5. All films showed almost the same rapid release rate in the first hour with the
percentage TPC release reached to 69.5%, 68.7%, and 62.6% for LMP-PE, SA-PE,
and TF-PE film, respectively. After the first hour, the release of TPC slowed down
significantly, especially for the SA-PE film. After 4 h, almost no change in TPC
release rate was observed in SA-PE film, but TPC release increased about 10% for
LMP-PE and TF-PE films between 8-24 h. At the end of 24 h, TPC release was 96.6%,
93.8%, and 80.5% for LMP-PE, TF-PE and SA-PE film, respectively.
Figure 4.5 TPC releasing characterization of wine grape pomace extract based
films in distilled water corresponding to time at room temperature. The results
are the mean of triplicates with standard deviations. LMP=low methoxyl pectin;
SA=sodium alginate; TF=Ticafilm® (mixture of sodium alginate, carrageenan
and cellulose gum).
0%
20%
40%
60%
80%
100%
0 4 8 12 16 20 24
Per
cen
tage
of
rele
ase
d T
PC
LMP-PE SA-PE TF-PE
Time (hr)
98
No previous study had simultaneously evaluated the film water solubility and
TPC release kinetics. In this study, TPC release and film solubility were not in
synchronization at the first 8 h of water immersion test, where the phenolic
compounds were rapidly released from the film matrix, but only LMP-PE film was
highly dissolved into water at the same time period (Figures 4.3 and 4.5). The initial
fast release of TPC was possibly caused by the quick dissolve of phenolic compounds
which were hydrophilic, bonded with film polysaccharides, and distributed on the
surface of the films. Along with the longer water immersion, the film structure relaxed
and the film matrix swollen, leading to slower release of phenolic compounds (Wu et
al., 2005). This might explain continuously increased TPC release from LMP-PE film
matrix while TPC release from SA-PE and TF-PE films tended to be stable from 8 to
24 h.
Several previous studies have evaluated the antioxidant properties of plant
extract incorporated films. Corrales et al. (2009) reported that the pea starch based
films incorporated with grape seed extract (lyophilized powder) showed a low TPC
migration (8%). Mayachiew and Devahastin (2010) added gooseberry concentrate into
chitosan based films and reported about 70 to 90% of TPC release from the films. The
TPC release from this study was comparable with the results from Mayachiew and
Devahastin (2010).
Antibacterial activity
Overall, all types of PE films significantly delayed the bacterial growth during
24 h of growth test (Figure 4.6). At the end of 24 h, about 2 log reduction in L.
innocua and ~5 log reduction in E. coli were observed compared with control (culture
without added PE film). Within the same bacteria strain, three film types showed
similar inhibition against the growth of L. innocua or E. coli, while the PE based films
performed differently against the growth of the two different bacteria. No growth in E.
coli cultures containing any PE film was observed during 24 h test, and a 4.9 log (TF-
PE film)-5.5 log (SA-PE film) reductions were achieved compared with control. While
for L. innocua, continuous growth during the 24 h test period was observed, but was
99
significantly slower than that of control (p<0.05). A 0.5-1.3 log reduction was
observed at the first 4 h, followed by 2.4-3.0 log reduction at 8 h, and at 1.7-3.0 log
reduction at 24 h compared with control. Hence, it could be concluded that all types of
PE films inhibited the growth of E. coli and L. innocua, but E. coli was more
susceptible to the PE films than that of L. innocua in this study.
WGP skins are rich in polyphenols, such as tannins, phenolic acids, and
flavanols, which are proven having antimicrobial functions through different
mechanisms including membrane disruption, bind to proteins, and formation of a
complex with bacteria cell wall (Cowan, 1999). In addition, WGP is abundant in
organic acids which have antibacterial activity against both Gram-negative and Gram-
positive bacteria (Daglia et al., 2007; Kim et al., 2008). In this study, the released TPC
and organic acids from the PE films may both play the roles as antibacterial agents.
However, the literature contains controversial reports on the efficacy of WGP against
Gram-positive or Gram-negative bacteria. Kataliníc (2010) reported that WGP skin
extracts inhibited the growth of both Gram-negative and Gram-positive
microorganisms. On the other hand, Ӧzkan et al. (2004) found that S. aureus (Gram-
positive) were more susceptible to grape pomace extracts (2.5%) than E. coli O157:H7
(Gram-negative bacteria) at the same concentration level. Corrales et al. (2009)
indicated that grape seed extract incorporated pea starch films were able to inhibit
Gram-positive, but not Gram-negative bacteria. This study demonstrated that the PE
films inhibited both Gram-positive and Gram-negative bacteria, but were more
effectively against Gram-negative bacteria (E. coli) than Gram-negative bacteria (L.
innocua).
100
Figure 4.6 The inhibiting activity of wine grape pomace extract based films
against E. coli and L. innocua corresponding to time at room temperature. The
results are the mean of triplicates with standard deviations. LMP=low methoxyl
pectin; SA=sodium alginate; TF=Ticafilm® (mixture of sodium alginate,
carrageenan and cellulose gum).
0
2
4
6
8
10
12
0 4 8 12 16 20 24
control TF-PE
LMP-PE SA-PE
Survival of E.coli
log
(CF
U/m
L)
Time (h)
0
2
4
6
8
10
12
0 4 8 12 16 20 24
control TF-PE
LMP-PE SA-PE
log
(CF
U/m
L)
Time (h)
Survival of L.innocua
101
Conclusion
Wine grape pomace extract based edible films with the addition of small
amount of polysaccharides showed attractive color and comparable mechanical and
water barrier properties to other edible films. All films had relatively low WVP. TF-
PE films had high tensile strength, and SA-PE and TF-PE films showed large
elongation. Hence, they may be used as colorful food wraps. The controlled release of
phenolics from the film matrix illustrated their potential antioxidant and antimicrobial
functions. LMP-PE film had high water solubility and fast phenolics release rate,
making it a good candidate as the oral fast dissolving film in pharmaceutical or other
similar applications.
Several respects are worthy further studies. First, it is necessary to enhance the
water extraction of bioactive compounds and soluble polysaccharides from WGP in
order to promoting the antioxidant capacity and antimicrobial functionality,
meanwhile reducing the usage of extra sources of polysaccharides. Further, film
forming formulations can be improved with the addition of other functional substances
to strengthen the film mechanical and water barrier properties for more wide
applications. Moreover, applications of wine grape pomace extract based edible films
and coating should be studied on real food systems for their antioxidant and
antimicrobial functions.
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106
CHAPTER 5
General Conclusion
This project was the first study that analyzed the chemical composition of wine
grape pomace (WGP) skins grown in the Pacific Northwest of the United States, and
used WGP extract to form edible films.
The obtained chemical composition data of WGP skins provide the guidance
for developing their innovating applications. The high contents of total phenolic
compounds (TPC) (21.4-26.7 mg gallic acid equivalent/g DM), antiradical scavenging
activity (RSA) (32.2-39.7 mg ascorbic acid equivalent/g DM), anthocyanins (ACY)
(0.29-0.89 mg malvidin-3-glucoside equivalent/g DM), total flavanol contents (TFC)
(42.6-61.2 mg catechin equivalent/g DM) and proanthocyanidins (PAC) (11.9-24.1 mg
condensed tannin/g DM) in red WGP (RWGP) skins make them excellent candidates
as food additives which provides food commodities (i.e. beverages, dairy products,
candies) with high antioxidant activity and bright red colors. RWGP skins are also
good sources of dietary fiber (54.7-61.2% DM) with high contents of Klason lignin
(32.0-41.0% DM), cellulose, and hemicellulose, hence are of great potentials of being
biodegradable packaging containers. The high contents of dietary fiber and
polyphenolic compounds also enable RWGP skins powder for direct usage in foods.
For instant, RWGP skins powder can be a substitute of bakery flour, and it also can be
added to meat products to prevent lipid oxidation and fortify them with dietary fiber.
On the other hand, the distinctively high amount of soluble sugar in the white WGP
(WWGP) skins (55.8-77.5% DM) may also make them form packaging materials with
excellent flexibility.
WGP skins (cv. Merlot) were employed to formulate edible films with the
addition of a small amount of polysaccharides. Pomace extract (PE) edible films
107
showed attractive color and comparable mechanical and water barrier properties to
other edible films. Hence, they may be used as colorful food wraps. The low methoxyl
pectin-PE (LMP-PE) film had high water solubility and fast phenolics release rate,
making it a good candidate as the oral fast dissolving film in pharmaceutical or other
similar applications. All PE based edible films were able to release phenolics and
prevent the growth of Escherichia coli and Listeria innocua in an aqueous system,
demonstrated their potentials as functional edible films with antioxidant capacity and
antimicrobial activity.
Several respects of this project, however, are worthy further studies. First,
further study is necessary to improve WGP preparation procedures for obtaining bright
color, appreciative aroma, more soluble fractions and nutrient compounds. Secondly,
more food applications of WGP skins can be developed based on the chemical
composition data from this project. Thirdly, further study should be addressed to
improve mechanical and mass barrier properties of PE films by incorporating with
other film forming materials, to enhance the antioxidant capacity and antimicrobial
activity by optimizing the polyphenolic recovery of extract from WGP skins, and to
apply PE based edible films on real foodstuffs.
108
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APPENDIX
Chromatograms and correction factors of neutral sugars
Neutral sugars (NS) were the monosaccharides from acid hydrolysis of the
structural carbohydrates (dietary fiber). NS of WGP were characterized by eluting
through Aminex HPX–87P column equipped in HPLC-ELSD. The chromatograms of
IDF and SDF in Pinot Noir are shown in Figure A.1 as the examples. Retention time
for sugar standards were 12.567 min for glucose, 13.604 min for xylose, 14.343 min
for glactose, 15.481 min for arabiose, and 15.983 min for mannose, respectively.
The effect of sulfuric acid hydrolysis on the changes of responding signals of
five sugars are reported in Table A.1. Acid hydrolysis increased the responding signals
in ELSD of five neutral sugars by 9% to 72%, possibly due to the water molecules
trapped in the CaCO3 precipitates when calcium carbonate neutralized the acid
solution, thereby increased the concentrations of sugars in aqueous system. Therefore,
the correction factors were taken into account in order to obtain accurate amount of
NS in the WGP. The real concentration of each neutral in WGP was obtained by
multiplying detected response of each neutral sugar by the corresponding correction
factor.
127
a. HPLC – ELSD chromatogram of neutral sugar of IDF in Pinot Noir
b.
c. HPLC – ELSD chromatogram of neutral sugar of SDF in Pinot Noir
Figure A.1 Neutral sugar of IDF and SDF in Pinot Noir analyzed by HPLC-
ELSD
Table A.1 Correction factors of each hydrolysis neutral sugar standard in IDF
and SDF after acid hydrolysis (AH)
Retention time
(min)
Det
ecto
r re
spo
nse
(mV
)
Retention time
(min)
Det
ecto
r re
sponse
(mV
)
128
Glucose Xylose Galactose Arabinose Mannose
IDF SDF IDF SDF IDF SDF IDF SDF IDF SDF
Original
conc.*
38.91 2.38 4.80 0.47 8.18 1.95 3.20 0.58 10.82 0.51
Conc.+ (after
AH)
41.77 3.24 6.29 0.81 9.07 2.30 3.60 0.39 11.76 0.42
Correction
factor++
0.93 0.73 0.76 0.58 0.90 0.85 0.89 1.49 0.92 1.21
*Original concentration for acid hydrolysis.
+ Detected concentration after acid hydrolysis.
++ Correction factor was equal to original concentration divided by detected
concentration after acid hydrolysis.
