estabilidade e homogeneização - tradução

8/2/2019 Estabilidade e homogeneizao - traduo

1/23

ForP

eerR

eview

The effect of homogenization on the stability of PineapplePulp

Journal: International Journal of Food Science and Technology

Manuscript ID: IJFST-2010-06128.R1

Manuscript Type: Original Manuscript

Keywords: Pineapple, Viscosity, Food Quality

Institute of Food Science and Technology

International Journal of Food Science & Technology


2/23

ForPeer

Review

1

The effect of homogenization on the stability of1

Pineapple Pulp2

Homogenization of Pineapple Pulp3

Silva, V. M.; Sato, A. C. K.; Barbosa, G.; Dacanal, G. .; Velsquez, H. J. C.; Cunha, R. L.*4

Department of Food Engineering - School of Food Engineering5

UNICAMP (University of Campinas), P.O. Box 6121, Post Code: 13083-862, Campinas, So6

Paulo, Brazil.7

*[email protected]; phone: +55 19 3521.4047; fax: +55 19 3521.40278

Keywords: pineapple pulp, stability, homogenization, sedimentation, viscosity9

ge 1 of 22 International Journal of Food Science & Technology
mailto:[email protected]:[email protected]:[email protected]


3/23

ForPeer

Review

2

ABSTRACT10

Pineapple pulp was homogenized at different pressures and its stability investigated by way of11

flow curves, particle size distribution, morphology, cloudiness and sedimentation. The12

particle size of the homogenized pulp ranged from 400 to 100 m for homogenization13

pressures of between 0 and 700 bar. The pineapple pulp showed shear thinning behaviour14

with increasing flow index (n) after processing at higher pressures. In addition, the pulps with15

smaller particles showed less serum cloudiness, even though the sedimentation tests showed16

the highest stability for pulp homogenized between 200 and 300 bar. Above 400 bar the pulp17

showed phase separation and higher sedimentation indexes, similar to that observed for the18

untreated samples, which was attributed to the formation of aggregates due to inter-particle19

attraction.20

21

INTRODUCTION22

Pineapple, Ananas comusus (L.) Merr., is an important fruit crop in many tropical and23

subtropical countries. It may be consumed fresh or in a number of processed forms such as24

juices, desserts or pulps to be added as ingredients in foods such as yoghurts and ice creams.25

Fruit pulps are complex multicomponent systems, opalescent or turbid due to the presence of26

insoluble solids in suspension (Benitez et al., 2007a). Pineapple pulps or juices are unstable27

suspensions that settle quickly after extraction, and such phase separation depreciates the28

visual appearance of the product. However, it is believed that a better definition of the29

manufacturing conditions would contribute to an increased stability of the juices (Beveridge,30

2002). Suspensions can be diluted with no particle-particle interactions, sterically stabilized,31

flocculated with a fully formed structure, partially stable with some structure formation or32

sedimentation.The formation of a structure depends on the chemical structure of both phases,33

Page 2International Journal of Food Science & Technology


4/23

ForPeer

Review

3

the particle size and shape, the surface effects and/or the presence of any additives (Ferguson34

& Kemblowski, 1991).35

Many investigations have been carried out on the stability of cloud suspensions in apple,36

pineapple, passion fruit and carrot pulps (Beveridge, 2002; Okoth et al., 2000; Liang et al.,37

2006; Mollov et al., 2006). The cloud components of fruit pulps can be classified into four38

categories: coarsely dispersed particles (> 1 mm) such as fibres, pulp particles and stone cells,39

which sediment rather quickly; finely dispersed particles (1~100 m) such as pulp fragments,40

cell aggregates, whole cells, cell wall fragments and starch particles, that sediment a little41

slower during storage due to their positively charged protein-carbohydrate-complexes42

surrounded by negatively charged pectin coatings; colloidal substances (0.1~0.001 m) such43

as pectin, hemicellulose, proteins and dissolved starch, in which sedimentation can only be44

caused by enzymatic activity; and emulsified substances (


5/23

ForPeer

Review

4

relationship. In general, higher pressure processing produces smaller particles, up to a certain58

limit of micronization.59

Rheological measurements have been considered as an analytical tool to provide a60

fundamental insight into the structural organization of foods (Rao, 1999). Various factors61

affect the rheological behaviour of fruit pulps, including temperature, total and soluble62

solids/concentration, size, shape, size distribution and the arrangement of the particles that63

compose the dispersed phase (Pelegrine et al., 2002).64

The stability of a suspension is very important for process control and as a quality65

parameter, and is affected by a number of factors, such as: the total solid content, particle size,66

particle shape and particle size distribution, that are closely related to the maximum packing67

fraction, which indicates the maximum amount of particles that can be packed into a given68

volume. Such stability may be closely associated with the rheological properties. Thus, the69

aim of this work was to evaluate the effects of different homogenization pressures on the70

rheological properties and stability of pineapple pulp.71

MATERIAL AND METHODS72

Material73

Frozen pasteurized pineapple pulp was acquired on the local market (DeMarchi,74

Jundia, So Paulo, Brazil), and characterized with 13.4 % of solids, 11.2 Brix, pH of 3.7675

and a density of 1.034 g/cm3. The pulp was centrifuged at 1000g for 30 minutes for serum76

separation, and the pulp content characterized as 45.5 %.77

Homogenization process78

The pineapple pulp was homogenized at 25C in a Panda 2K NS1001L (Niro Inc.,79

Hudson, Ohio, USA) homogenizer, using pressures varying from 50 to 700 bar (5 to 70 MPa).80

Potassium sorbate was added to the pineapple pulps at 0.1% w/w to avoid fungal growth, and81



6/23

ForPeer

Review

5

the pulps were analysed for particle size distribution, rheological measurements, optical82

microscopy, cloudiness and stability to sedimentation.83

Particle size distribution84

The particle size distribution and mean volumetric diameter D [4,3] (Equation 1) of85

the raw and homogenized pineapple pulps were obtained using a Mastersizer Laser Light86

Scattering Spectrometer (model MAM 5005, Malvern Instruments Ltd., Worcester,87

Worcestershire, U.K) by dispersing the samples into deionized water. The measurements were88

taken in quintuplicate and the difference between the D [4,3] evaluated using the Tukey test.89

[ ]

=

==n

i

i

n

i

i

dn

dn

1

3

1

4

.

.

4,3D

((1)

Where diis the diameter of the particles in the sample and n is the number of particles.90

Rheological measurements91

The flow property measurements were performed using a controlled stress rheometer (Carri-92

Med CSL2 500, TA Instruments, New Castle, Delaware, USA) at 25C. Parallel stainless93

steel plates with a rough surface (4 cm diameter and 1.25 mm gap) were used for the94

measurements. Prior to analysis, the product was gently mixed to homogenize the sample and95

all experiments were performed at least in triplicate. Flow curve measurements were carried96

out with a shear rate ranging from 0 to 300 s -1 in three sweeps (up, down and up-cycles), to97

evaluate thixotropy. The data obtained from the third sweep were fitted to the power law98

model (n

k &= ), where is the shear stress (Pa), & the shear rate (s-1

), k the consistency99

index (Pa sn) and n is the flow behaviour index (dimensionless). Flow curves were adjusted by100

a non-linear regression analysis using the Statistica 5.0 software (StatSoft, Tulsa, Oklahoma,101

USA).102



7/23

ForPeer

Review

6

Optical microscopy103

The particles of the raw and homogenized pineapple pulp were diluted and coloured104

with a diluted violet crystal solution. The product was then deposited and dispersed on a glass105

slide to be observed under a stereomicroscope (Citoval 2, Zeiss, Jena, Thringen, Germany)106

equipped with a Kodak zoom digital camera model EasyShare DX4530 (Eastman Kodak107

Company, Rochester, Minnesota, USA). The images were captured at least in quintuplicate108

for each sample.109

Stability110

Sedimentation test111

Raw and homogenized pineapple pulps were transferred to graduated 100 ml tubes,112

stored at 25C and observed for 12 days. The volume of sediment was measured (total volume113

minus the serum phase) and the sedimentation index calculated as follows:114

totalV

VIS inf=

(2)

where Vinf is the sediment volume (ml) and Vtotal is the total volume of the sample115

(ml).116

Cloudiness117

118

Twenty five millilitres of pulp were added to 75 mL of water and centrifuged at 320 g119

for 10 min (Novatecnica NT810, Atibaia, So Paulo, Brazil). The optical density (absorbance)120

of the supernatant (serum phase) was determined at 660 nm using a spectrophotometer121

(Beckman DU640, Corona, California, USA) with distilled water as the reference. Turbidity122

measurements allow for the determination of the amount of light absorbed by the suspended123

particles in the beverage, thus higher absorbance readings correspond to greater cloudiness124

(Okoth et al., 2000).125



8/23

ForPeer

Review

7

RESULTS AND DISCUSSION126

Optical microscopy127

The micrographs showed that the homogenization of the pineapple pulp considerably128

reduced the size of the suspended particles, as compared to the non-homogenized pulp (Fig.129

1).130

It can be seen that the non-homogenized pulp (0 bar) consisted mainly of large131

deformable particles with irregular shapes and a number of small particles (Fig. 1a). In this132

case, the larger particles were associated with whole cells or aggregates, while the latter were133

related to other cell materials, such as cells from the parenchyma tissue (Ouden and Vliet,134

1997). During homogenization, these suspended particles were broken down resulting in a135

pulp with a large number of small particles such as fibrous particles, cells, cell wall fragments136

and polymers, amongst others (Figs. 1b and 1c), forming a new structure. In this case, the137

smaller particles formed a network different from that observed in the non-homogenized pulp,138

even though their shape/surface contour remained irregular. The same behaviour was139

observed by Bayod et al. (2007) for tomato suspensions before and after the process of140

homogenization.141

Particle size distribution142

Fig. 2 shows that the pineapple pulp presented a monomodal particle size distribution,143

independent of the pressure evaluated. The mean particle size decreased with increase in the144

homogenization pressure, with significant differences (p


9/23

ForPeer

Review

8

m for 0, 50 and 100 bar, respectively, whilst higher homogenization pressures only150

promoted smaller reductions in the mean particle size (D[4,3]).151

In addition to the evolution of the distribution to smaller sizes, the increase in152

homogenization pressure led to a narrower distribution, indicating greater uniformity, even153

though the mean diameter did not vary much for pressures above 200 bar. The154

homogenization process can reduce the size of the coarser particles leading to an increase in155

the concentration of fine particles. A similar behaviour was observed by Bayod et al. (2007)156

for tomato suspensions.157

Rheological measurements158

None of the pulps evaluated showed differences between the first and third shear159

cycles (data not shown), indicating that the samples were not dependent on the time of shear,160

i.e., they are not thixotropic or rheopetic.161

The power law model was adequate to fit the flow behaviour of the pineapple pulp,162

showing high determination coefficients (R > 0.99). The pineapple pulp showed shear163

thinning behaviour for all working pressures, without significant yield stress (Fig. 3). Similar164

behaviour was observed in previous studies for other fruit products, such as jaboticaba (Sato165

& Cunha, 2009), guava (Ferreira et al., 2002), pineapple (Pelegrine et al., 2000), araa166

(Haminiuk et al. 2006) and aai (Tonon et. al., 2009) pulps, without a homogenization167

process. The consistency index (k) decreased from 3.48 to 0.24 Pa.sn, whereas the flow168

behaviour index (n) increased from 0.29 to 0.55 as the working pressure increased from 0 to169

700 bar (Inset Table on Fig. 3), i.e. the decrease in particle size promoted an increase in170

flowability as observed for green chilli puree (Ahmed et al., 2000). The serum pulp was also171

evaluated and showed a consistency index (k) of 0.005 Pa.sn

and a flow behaviour index (n)172

of 0.94.173



10/23

ForPeer

Review

9

The viscosity was evaluated at different shear rates of 1, 10 and 100 s-1

(Fig. 4).174

Increasing the working pressures up to 200 bar led to a more pronounced drop in viscosity as175

in the case of the particle size reduction (Fig. 2), while only a slight reduction in viscosity was176

observed from 200 bar to 700 bar. A similar result was observed by Schijvens et al. (1998) for177

applesauce. However, the opposite behaviour was observed for tomato pulp (Kalamaki et al.,178

2003; Ouden & Vliet, 2002), coconut milk (Chiewchan et al., 2006) and carrot juice179

(Sichaipanit & Kerr, 2007), when an increase in the apparent viscosity was observed with180

decreasing particle size. Such a difference can be attributed to the fact that the breakup of181

some tissues such as tomato cells during homogenization is much more intense than for182

applesauce cells (Ouden & Vliet, 2002). According to Guyot et al. (2002), it is still not183

possible to predict a priori how a complex particle size distribution will affect the viscosity of184

a dispersion of small particles. However one can speculate that the pineapple pulp might185

behave in a manner more similar to that of the applesauce, in which the cells show186

considerable brightness under polarized microscopy, indicating the presence of semi-187

crystalline structures, probably mainly cellulose present in the relatively thick cell walls.188

Stability189

Cloudiness190

The cloud is a result of dispersed insoluble particles such as pectin, protein, lipids,191

cellulose and hemicelluloses (Scott et al. 1965). Fig. 5 shows the relationship between192

cloudiness and homogenization pressure/mean particle size of pineapple pulp. It can be seen193

that an increase in homogenization pressure from 0 to 700 bar decreased pulp cloudiness due194

to the decrease in particle size, with a greater reduction up to 200 bar. Decreased cloudiness195

with increasing homogenization pressure can be attributed to the decrease in particle size,196

which allows more light to go through the juice (Okoth et al., 2000).197



11/23

ForPeer

Review

10

Sedimentation test198

Fig. 6 shows the sedimentation index as a function of storage time for the several199

homogenization pressure treatments. In the first 24 hours, only the sample that had not been200

homogenized showed phase separation, which is common behaviour for some fruit pulps201

(Beveridge, 2002, Neidhart et al., 2002, Okoth et al., 2000). After the first day of storage,202

samples treated with pressures equal or higher than 400 bar started to show particle203

sedimentation, while the pulps homogenized at 50 bar only showed particle sedimentation as204

from the 5th

day. In this case, pressures higher than 400 bar did not prevent phase separation205

due to the low viscosities of these samples, insufficient to maintain the stability of the system.206

On the other hand, pulps subjected to pressures of 100, 200, 250 and 300 bar were stable207

throughout the observation period (10 days), showing that these pressure treatments could be208

used to stabilize pineapple pulp. It should be emphasized that, even though the particle sizes209

obtained after the homogenization treatments in the present work did not approach the values210

of 0.5 to 2 m required to stabilize some fruit juices (Beveridge, 2002), stabilization was211

obtained for particles with D[4,3] ranging from 125 175 m.212

Stokes law relates the sedimentation velocity to the properties of the particles and213

suspending medium. In general, according to Stokes law, the particle size and/or the214

difference between the densities of the particles and the medium are crucial factors affecting215

the stability of a suspension. Since the continuous medium is the same for all the samples216

(pulp serum), it would be expected that more stable pulps would be obtained with smaller217

particles. However, it should be considered that surface forces, such as van der Waals218

attraction, are more significant for smaller particles, while larger particles are basically219

influenced by hydrodynamic forces (Genovese et al., 2007). Thus it could be expected that the220

smaller particles produced by higher homogenization pressures, would form aggregates due to221



12/23

ForPeer

Review

11

forces of attraction, even though the particle sizes are not in the colloidal domain. The smaller222

the particles are, the stronger the attractive forces, leading to larger aggregates and,223

consequently, faster sedimentation.224

CONCLUSIONS225

A stable pineapple pulp with negligible phase separation within the period evaluated226

was obtained for dispersions processed within the pressure range from 100 to 300. Under227

these conditions, the coarse particles were reduced in size to the range between 175 and 125228

m, respectively. Even though higher homogenization pressures reduced the particle size even229

more, sedimentation was observed when pressures above 400 bar were applied, and the230

highest sedimentation index was observed for samples treated at 700 bar. Such results indicate231

that Stokes law did not explain the stability of pineapple pulp in the present study,232

emphasizing the importance of inter-particle forces. Thus it was suggested that apart from233

hydrodynamic forces, surface forces, such as van der Waals attraction, should be considered234

even for particles of about 100m, classified as non-colloidal.235

ACKNOWLEDGEMENTS236

The authors gratefully acknowledge Conselho Nacional de Desenvolvimento Cientfico e237

Tecnolgico (CNPq, process number 301869/2006-5) for the financial support.238

239

REFERENCES240

Ahmed, J., Shivhare, U.S. & Raghavan, G.S.V. (2000). Rheological characteristics and241

kinetics of colour degradation of green chilli puree. Journal of Food Engineering, 44, 239-242

244.243

Askar, A. & Treptow, H. (1992).Trubstabile und hochwertige Nektare aus tropischen244

Frchten (in English). Confructa Studien, 36, 130-153.245



13/23

ForPeer

Review

12

Bayod, E., Mansson, P., Innings, F., Bergenstahl, B. & Tornberg, E. (2007). Low Shear246

Rheology of Concentrated Tomato Products Effect of Particle Size and Time. Food247

Biophysics, 2, 146-157.248

Benitez, E.I., Genovese, D.B. & Lozano, J.E. (2007a). Effect of pH and ionic strength on249

apple juice turbidity: Application of the extended DLVO theory. Food Hydrocolloids, 21,250

100109.251

Benitez, E.I., Genovese, D.B. & Lozano, J.E. (2007b). Scattering efficiency of a cloudy apple252

juice: Effect of particles characteristics and serum composition. Food Research International,253

40, 915922.254

Betoret, E., Betoret, N., Carbonell, J. V. & Fito, P. (2009). Effects of pressure255

homogenization on particle size and the functional properties of citrus juices.Journal of Food256

Engineering, 92, 18-23.257

Beveridge, T. (2002). Opalescent and cloudy fruit juices: formation and particle stability.258

Critical Reviews in Food Science and Nutrition, 42, 317-337.259

Chiewchan, N., Phungamngoen, C. & Siriwattanayothin, S. (2006). Effect of homogenizing260

pressure and sterilizing condition on quality of canned high fat coconut milk.Journal of Food261

Engineering, 73, 3844.262

Ferguson, J. & Kemblowski, Z. (1991). Applied Fluid Rheology. Pp 1-323. New York, USA:263

Elsevier Applied Science.264

Ferreira, G.M., Queiroz, A.J.M., Conceio, R.S. & Gasparetto, C.A. (2002). Effect of265

temperature on the rheological behavior of guava and cashew apple pulps (in Portuguese).266

Revista de Cincias Exatas e Naturais, 4, 175184.267



14/23

ForPeer

Review

13

Genovese, D.B.; Lozano, J.E.; Rao, M.A. (2007). The rheology of colloidal and noncolloidal268

food dispersions.Journal of Food Science, 72, R11-R20.269

Guyot, A., Chu, F., Schneider, M., Graillat, C. & Mckenna, T. F. (2002). High Solid content270

latexes. Polymer Science, 27, 1573-1615.271

Haminiuk, C.W.I., Sierakowski, M.R., Vidal, J.R.M.B. & Masson, M.L. (2006). Influence of272

temperature on the rheological behavior of whole ara pulp (Psidium cattleianum sabine).273

Lebensmittel-Wissenschaft und Technologie, 39, 426430 (research note).274

Innings, F. & Trgardh, C. (2007). Analysis of the flow field in a high-pressure homogenizer.275

Experimental Thermal and Fluid Science, 32, 345354.276

Kalamaki, M. S, Powell, A.L.T, Struijs, K., Labavitch, J.M., Reid, D.S. & Bennett, A.B.277

(2003). Transgenic Overexpression of Expansin Influences Particle Size Distribution and278

Improves Viscosity of Tomato Juice and Paste. Journal of Agriculture and Food Chemistry,279

51, 7465-7471.280

Liang, C., Hu, X., Ni, Y., Wu, J., Chen, F. & Liao, X. (2006). Effect of hydrocolloids on pulp281

sediment, white sediment, turbidity and viscosity of reconstituted carrot juice. Food282

Hydrocolloids, 20, 11901197.283

Mollov, P., Mihalev, K., Buleva, M. & Petkanchin, I. (2006). Cloud stability of apple juices in284

relation to their particle charge properties studied by electro-optics. Food Research285

International, 39, 519524.286

Neidhart, S., Reiter, M, Mensah-Wilson, M., Stemmer, G., Braig, C., Sevin S. & Carle, R.287

(2002). In Possibilities for Improving Quality of Fruit Juices and Drinks from Tropical Fruits288

by Homogenization and Addition of Pectin, International Symposium Sustaining Food289



15/23

ForPeer

Review

14

Security and Managing Natural Resources in Southeast Asia - Challenges for the 21st

Century,290

Chiang Mai, Thailand, jan 8-11.291

Okoth, M.W., Kaahwa, A.R. & Imungi, J.K. (2000). The effect of homogenization, stabilizer292

and amylase on cloudiness of passion fruit juice. Food Control, 11, 305-311.293

Ouden, F.W.C. den & Vliet, T.van. (1997). Particle size distribution in tomato concentrate294

and effects on rheological properties.Journal of Food Science, 62, 565567.295

Ouden, F.W.C. den & Vliet, T.van. (2002). Effect of concentration on the rheology and serum296

separation of tomato suspensions. Journal of Texture Studies, 33, 91-104.297

Pelegrine, D.H., Silva, F.C. & Gasparetto, C.A. (2002). Rheological Behaviour of Pineapple298

and Mango Pulps.Lebensmittel-Wissenschaft und Technologie, 35, 645-648.299

Pelegrine, D.H., Vidal, J.R.M.B. & Gasparetto, C.A. (2000). Study of apparent viscosity of300

mango (Keitt) and pineapple (Prola) pulps (in Portuguese). Cincia e Tecnologia de301

Alimentos, 20, 128-131.302

Rao, M. A. (1999).Rheology of Fluid and Semisolids Fluids: Principles and applications. Pp303

1-429. Maryland, USA: Aspen Publishers Inc.304

Sato, A. C. K. & Cunha, R. L. (2009). Effect of particle size on rheological properties of305

jaboticaba pulp.Journal of Food Engineering,91, 566-570.306

Scott, W.C., Kew, T.J. & Veldhuis, M.K. (1965). Composition of orange juice cloud.Journal307

of Food Science, 30, 833.308

Sinchaipanit, P. & Kerr, W.L. (2007). Effect of reducing pulp-particles on the physical309

properties of carrot juice.ASEAN Food Journal, 14, 205-214.310



16/23

ForPeer

Review

15

Tonon, R.V., Alexandre, D., Hubinger, M.D. & Cunha, R.L. (2009). Steady and dynamic311

shear rheological properties of aai pulp (Euterpe oleraceae Mart.). Journal of Food312

Engineering, 92, 425431.313



17/23

ForPeer

Review

16

Legends to Figures314

Figure 1 Microscopical images of pineapple pulp after homogenization at (a) 0 (non-315

homogenized), (b) 300 and (c) 600 bar of pressure.316

Figure 2. Particle size distribution of pineapple pulp homogenized at the different pressures.317

Inset Table shows the volume mean diameter of these samples.318

Figure 3 Flow curves for pineapple pulp homogenized at different pressures. Inset Table319

shows the rheological parameters of the power law model fitted to the flow behavior of the320

pineapple pulp homogenized at different pressures. Different letters indicate significant321

difference (p


18/23

ForP

eerR

eview

Microscopical images of pineapple pulp after homogenization at (a) 0 (non- homogenized), (b) 300and (c) 600 bar of pressure.23x10mm (600 x 600 DPI)

ge 17 of 22




19/23

ForP

eerR

eview

Particle size distribution of pineapple pulp homogenized at the different pressures. Inset Tableshows the volume mean diameter of these samples

25x17mm (600 x 600 DPI)

Page 18




20/23

ForP

eerR

eview

Flow curves for pineapple pulp homogenized at different pressures. Inset Table shows therheological parameters of the power law model fitted to the flow behavior of the pineapple pulphomogenized at different pressures. Different letters indicate significant difference (p


21/23

ForP

eerR

eview

Viscosity of the pineapple pulp at different shear rates as a function of homogenization pressure andparticle size (inset Figure).40x26mm (600 x 600 DPI)

Page 20




22/23

ForP

eerR

eview

Correlation between cloudiness and homogenization pressure/volume mean diameter (inset Figure)24x16mm (600 x 600 DPI)

ge 21 of 22




23/23

ForP

eerR

eview

Sedimentation index as a function of storage time for the several homogenization pressuretreatments

40x26mm (600 x 600 DPI)


estabilidade e homogeneização - tradução

Documents