c

, Mu

in a. mh anin tg prevae rekagg st

are asnence. Anthocyanins (E163) are avonoid p

fruitsdant af neurak & Zct ofn nutrg, Chiaing pig

the level of incorporation are administered by the regulatory

structural changes in food like starch gelatinization, protein denatur-

are available.

Food Research International 50 (2013) 641646

Contents lists available at ScienceDirect

Food Research

e lsrequirements of the individual countries. Maximum limits on levelsof addition of synthetic colours are imposed by many countries, butthe use of anthocyanin often has no numerical limit, and maximumdose is simply that which is sufcient to give the desired colourstrength (Henry, 1992). However, colour stability of anthocyaninsdepends on a number of factors such as the structure andconcentration of the anthocyanin, pH, temperature, oxygen and

To the best of our knowledge, stability of added anthocyanins aspre-extrusion colouring has not yet been reported in literature. Thepresent work reports on optimising the quantity and the stability ofanthocyanin for pre-extrusion colouring as a function of extrusionvariables. Further, the effect of citric acid and sodium bicarbonate, andevaluation of packaging material for coloured extrudates were alsoundertaken.presence of complexing agents such as pheKhairul, & Maziah, 2007).

Extrusion cooking is versatile and time eprocessing. It involves continuous cooking

Corresponding author. Tel.: +91 22 33611111; fax:E-mail address: rs.singhal@ictmumbai.edu.in (R.S. Si

0963-9969/$ see front matter 2011 Elsevier Ltd. Aldoi:10.1016/j.foodres.2011.05.017oration into numerouscolourants in foods and

Prior, 2009) and use of ascorbic acid to reduce the loss of anthocyaninsduring extrusion (Chaovanalikit, Dougherty, Camire, & Briggs, 2003)and this property facilitates their incorpaqueous food systems. However, usage ofpounds, widely distributed among(Wissgott & Bortlik, 1996). Antioxiplays a key role in the prevention oillnesses, cancer and diabetes (Konczseveral studies focusing on the effetreatments (Lule & Xia, 2005), huma2004), and its biological activity (Kon2003). These attractive natural colourhenolic colouring com-, berries and owersctivity of anthocyaninsonal and cardiovascularhang, 2004). There areanthocyanins in cancerition (Stintzing & Carle,, Goh, Chia, & Brouillard,ments are water-soluble

post-extrusion. However the use of natural colours prior to extrusionwould not only add to visual appeal and acceptability, but could alsoform a suitable matrix for delivery of nutraceutical phytochemicals toconsumers. This necessitates evaluation of stability of thesephytochemicals.

Reports on loss of indigenous anthocyanins (55%) in blue and redpigmented maize during extrusion processing (Mora-Rochin et al.,2010), and that present in cranberry pomace added to corn starch(White, Howard, & Prior, 2010), or grape pomace (Khanal, Howard, &nols and metals (Janna,

fcient process in food, mixing and forming

2. Materials and

2.1. Materials

Rice (Oryza sMumbai. Rice wwas packed in p

+91 22 24145614.nghal).

l rights reserved.roducts are not coloured, and are also avoured

any food product. With increasing psynthetic colourants, natural coloursoncern on the safety ofsuming greater promi-

ation, vitamin and pigment degradation (Harper, 1981). Generally,the extruded pColour in food system plays a vital role in consumer acceptance ofublic cStability of anthocyanins as pre-extrusion

Arvind V. Durge, Shatabhisa Sarkar, Rekha S. SinghalFood Engineering and Technology Department, Institute of Chemical Technology, Matunga

a b s t r a c ta r t i c l e i n f o

Article history:Received 3 February 2011Accepted 12 May 2011

Keywords:Pre-extrusion colouringAnthocyaninStabilityExtrusion

The suitability of anthocyanof extrusion parameters vizanthocyanin increased witdecreased with an increasestability of extrudates durinconditions (302 C) were18.2% which could reduce thwas found to be a better paclight as well as losses durin

1. Introduction

j ourna l homepage: www.olouring of rice extrudates

mbai 400 019, India

s a pre-extrusion colour nutraceutical of rice our was evaluated as a functionoisture content, screw speed and temperature of extrusion. The retention ofincrease in the moisture content of feed material and screw speed, but

he die temperature. The effect of citric acid and sodium bicarbonate on colourocessing, and that of light and packaging materials during storage at ambientluated. Addition of 1% citric acid increased the retention of anthocyanin up toquirement of pre-extrusion colouring by almost 25%. Metallized polyethyleneing material than low density polyethylene and protected the extrudates fromorage.

2011 Elsevier Ltd. All rights reserved.

process. The processing conditions used in extrusion cooking (hightemperature and lowwater content) result in numerous chemical and

International

ev ie r.com/ locate / foodresmethods

ativa) was procured from local market of Matunga,as ground to our to pass through 840 m and ourolyethylene bags. Anthocyanin extracted from red

642 A.V. Durge et al. / Food Research International 50 (2013) 641646carrot in the powder form (98% purity, pH stability 4.0 to 6.0) wasprocured from Indian Trading Company, Mumbai, kept in a refriger-ator (102 C) until further use. Packaging materials were procuredfrom Shako Flexipack Pvt. Ltd., Sion Mumbai. Citric acid and sodiumbicarbonate (food grade) were procured from SD Fine Chemicals,Mumbai, India. All chemicals used for analysis were of AR grade.

2.2. Methods

2.2.1. Preparation of sampleMoisture content (MC) of rice our was determined by (AACC,

1976) and calculated amount of distilled water was added to the ourandmixed thoroughly to assure uniform distribution to obtain desiredMC. The mixture was then packed in air tight jars and allowed toequilibrate overnight prior to extrusion.

2.2.2. Optimization of anthocyanin content in extruded rice ourColour percentage was varied from 1% to 3% (w/w) and extrusion

parameters were kept constant at feed moisture content (MC) of 14%,die temperature of 160 C, a screw speed of 150 rpm, and a feed rate of70 g/min. Extrusion cooking of conditioned ourwas carried out usingBrabender single screw extruder (Model No. 8 235 00, Germany), with20:1 barrel length to diameter ratio and a screw with compressionratio of 2:1. The extruder was tted with a die nozzle of 5 mmdiameter. Sensory evaluation of the rice extrudates was optimised forthe content of pre-extrusion addition of anthocyanin. Sensoryevaluation was done on a hedonic scale of 19 using 10-memberpanel as follows: 9like extremely, 8like very, 7like moderatelymuch, 6like slightly, 5neither like nor dislike, 4dislike slightly,3dislike moderately, 2dislike very much, and 1dislike (Camire,King, & Bittner, 1991).

2.2.3. Optimization of extrusion processing parametersThe extrusion processing conditions were carried out by varying

the MC from 14% to 18%, screw speed from 150 rpm to 170 rpm, anddie temperature from 140 C to 180 C. The extrudates were sealed inpolyethylene bags and stored in desiccators until further analysis.

2.2.4. Analysis of the coloured extrudates

2.2.4.1. Colour measurement (Hunter L*, a* and b* values). The colour ofextrudates was measured using Hunter Lab Colourimeter (ModelDP-9000 D25A), (Hunter associates laboratory, Reston, VA, USA) interms of Hunter L* value (lightness, ranging 0100 indicating black towhite), a* value (+a* value indicates redness anda* value indicatesgreenness) and b* value (+b* value indicates yellowness and b*value indicates blueness) (Camire, Chaovanalikit, Dougherty, & Briggs,2002). The samples were ground and passed through a 40 micronsieve prior to analysis.

2.2.4.2. Retention of anthocyanin colour. The retention of anthocyaninwas done by extraction with methanolic HCl by the method ofDelgado-Vargas, Jimenez, Paredes-Lopez, and Francis (2000) withmodications. The ground coloured extrudates (5 g) was extracted in25 ml of solvent (1% acidied methanol: water in 1:1 ratio) and kepton rotary shaker (200 rpm) for 24 h followed by centrifugation at8000 g. The supernatant so obtained was ltered and the clearsupernatant which was analysed at 537 nm in a Helios () UVvisspectrophotmeter (Thermoelectron, Erlangen, Germany) for quanti-cation. Quantication was carried on the basis of a standard plotobtained using 0.01.0 mg/ml anthocyanin that was procured fromthe Indian Trading Company, Mumbai. All analyses including thestandard graph was carried out in triplicates.

2.2.4.3. Organoleptic evaluation of anthocyanin coloured extrudate.

Acceptability of extrudates was determined by sensory evaluationusing 10-member panel on nine point hedonic scale as describedabove.

2.3. Effect of additives, packaging material and light on colour ofretention in anthocyanin-coloured extrudates

Effects of addition of citric acid and sodium bicarbonates on colourstability of extrudates of nal sample with desirable properties werecarried out. Both the additives were used at 1% and 2% w/w basis.Further, on the basis of the results obtained, the content ofanthocyanin added prior to extrusion in our supplemented with1% citric acid was carried out and analysed for retention andorganoleptic quality. Anthocyanin coloured extrudates with desirableproperties were packed in LDPE and metallized polyethylene, storedat ambient temperature (302 C), and evaluated for percentretention of colour during a 45 days storage study. Similarly packedsamples were stored under light intensity of 500 lx (lux), and studiedfor % retention of colour during 28 days storage. Further, a semi-logplot of percentage retention of percent retention of colour vs. days(Cai, Sun, & Corke, 1998) was done to obtain the rate constant (k) asthe slope of the graph. Half-life (t1/2), the time required for theanthocyanin was calculated from the rate constant as 0.693/k.

2.4. Statistical analysis

All the results were statistically analysed by Tukey's test (t-test) ata probability level of 5% (pb0.05) using the statistical programmeknown as NCSS-PASS software.

3. Results and discussion

3.1. Optimization of content of anthocyanin for pre-extrusion of riceextrudates

Anthocyanin in the powder form was added at 1, 2 and 3% (w/w)to rice our after equilibration to 14% MC and extruded at a dietemperature of 160 C and screw speed of 150 rpm. All the extrudateshad moisture content below 7%. Hence they were evaluated for theirsensory quality using a 10-member panel without any further drying.Rodrguez-Miranda et al. (2011) found the moisture content inextruded snacks prepared from our blends of taro and nonnixtama-lized maize to be lower than 10% which prevented spoilage ofextruded products. The extrudates containing 1, 2 and 3% anthocyaninshowed a sensory rating of 6.500.37, 8.450.22, and 7.250.17,respectively, suggesting that all the products were acceptableorganoleptically . The extruded sample with 2% anthocyanin wasmost acceptable in terms of appearance, colour and overall accept-ability, and therefore used for further studies.

3.2. Optimization of extrusion processing parameter on anthocyaninretention

3.2.1. Colour measurementThe visual appeal of colour makes it an extremely important quality

parameter and is directly related to the acceptability of food products.The colour characteristics of anthocyanin coloured extrudates weremeasured in terms of L*, a* and b* values. The L* value of extrudatesincreased with an increase in temperature from 140 to 180 C, anddecreased with an increase in MC of feed material from 14 to 18%(Table 1). The a* value of anthocyanin coloured extrudates increasedwith an increase inMC and screw speed, and decreasedwith an increasein temperature (Table 1). The increased a* value at higher MC may bedue to the entrapment of the pigments in denser matrix of the product.The residence time of rawmaterial decreased with an increase in screwspeed which resulted in minimum thermal treatment and thereby

higher retention of colour. A decrease in the redness of extrudates with

Table1

Effect

ofextrusionvariableson

Lvaluea

andavaluea

ofrice

extrud

ates

containing

pre-extrusionaddition

ofan

thocyanin.

Tem

(C)

14%moistureconten

t16

%moistureconten

t18

%moistureconten

t

Screw

speed(rpm

)

150

170

190

150

170

190

150

170

190

La

La

La

La

La

La

La

La

La

140

54.12

0.18

a8.47

0.03

a53

.52

0.23

a8.52

0.05

a52

.98

0.34

a8.58

0.04

a51

.84

0.25

a9.36

0.12

a51

.54

0.21

a9.48

0.03

a51

.26

0.09

a9.51

0.09

a47

.06

0.11

a10

.70

0.07

a46

.82

0.04

a10

.82

0.06

a46

.0

0.07

a10

.94

0.21

a

160

55.65

0.08

b8.06

0.11

b55

.40

0.13

b8.19

0.07

b54

.89

0.16

b8.10

0.23

b53

.30

0.14

b8.5

0.03

b53

.25

0.06

b8.34

0.04

b52

.65

0.50

b8.51

0.06

b49

.77

0.11

b9.57

0.05

b49

.25

0.08

b9.64

0.05

b48

.10

0.04

b9.75

0.06

b

180

57.68

0.11

c7.23

0.06

c57

.31

0.12

c7.36

0.03

c56

.58

0.09

c7.38

0.01

c56

.87

0.06

c8.21

0.13

c55

.41

0.10

c8.28

0.07

c54

.84

0.08

c8.28

0.07

c51

.45

0.10

c9.12

0.02

c50

.62

0.14

c9.32

0.07

c50

.21

0.05

c9.37

0.04

c

Means

withdifferen

tsupe

rscriptin

thesamecolumnaresign

icantly

differen

t(P

b0.05

).aRe

sultsarethemeanSD

ofthreede

term

inan

ts.

643A.V. Durge et al. / Food Research International 50 (2013) 641646increasing temperature was induced by pigment destruction asanthocyanins are sensitive to thermal processing. The b* value of theanthocyanin coloured extrudates under different processing conditionsare shown inTable 2. The b*valuewas signicantly affectedbyextrusionprocessing parameters and decreased from 3.350.05 to 0.830.02showing reddish blue colour. Recent reports have indicated the stabilityof anthocyanins from blueberries to be sensitive to individual andcombined effect of temperature, pressure, treatment time (Buckow,Kastell, Terefe, & Versteeg, 2010), the mechanisms and kinetics ofdegradation of anthocyanins (Patras, Brunton, O'Donnell, & Tiwari,2010), and protective effect of additives such as -cyclodextrin(Mourtzinos et al., 2008) and copigmentation with polyphenols (DelPozo-Insfran, Balaban, & Talcott, 2006).

3.2.2. Retention of anthocyanin in extrudatesAnthocyanin retention increased by increasingMC of feedmaterial

and screw speed, and decreasing temperature. A maximum retentionof 56.580.26% was seen at a higher MC of 18%, screw speed of190 rpm and lower temperature of 140 C. As the temperatureincreased to 180 C, retention decreased to 41.081.01% conrmingthe sensitivity of anthocyanin to temperature (Table 2). Shih, Kuo, andChiang (2009) reported 49% loss of anthocyanins during cabinetdrying of blueberries (Vaccinium corymbosum L.).

3.2.3. Organoleptic evaluation of anthocyanin-coloured extrudateThe selected anthocyanin coloured extrudates were evaluated

organoleptically (Table 3). Extrudates were selected on the basis oftheir percent colour retention and physical properties (data notreported). All the samples selected were acceptable and had sensoryscores above 6.0. Amongst these samples, the one extruded at 16%MC,die temperature of 160 C and screw speed of 190 rpm was mostacceptable in terms of appearance, colour, textural properties andoverall acceptability with best sensory score of 8.000.35. Althoughextrusion of rice with 18% MC at die temperature of 140 C and screwspeed of 150 rpm had a higher score for colour and maximum percentcolour retention of anthocyanin, but sensory score was lower at6.550.44. The physical properties were also not desirable at 18%MCand low die temperature of 140 C. Thus the sample with 16% MC andextruded at die temperature of 160 C and screw speed of 190 rpmhad optimum appearance, colour, texture and overall acceptability.

3.2.4. Optimised conditions for extrusionThe samples extruded at 14% MC, die temperature of 180 C and

screw speed of 150 rpmhad aminimum retention of 25.580.28%. Thesample at 18% MC, die temperature of 140 C, and screw speed of190 rpm had maximum colour retention of 56.580.26%, but showedanundesirable hard texture. Hence, samples at 16%MC, die temperatureof 160 C, and screw speed of 170 rpmwere considered as the optimumsince it had anoptimumhardness and good retention of colour (41.770.66%). This sample was then used for all further studies.

3.3. Effect of additives on colour of extrudates

The effect of addition of citric acid and sodium bicarbonates at 1and 2% (w/w) on colour stability of extrudates was then undertaken(Table 4). These additives were selected due to their ability to alter thepH which is known to affect the stability of anthocyanins. Further-more, the concentration was chosen so as not to adversely affect tasteof the extrudates. Citric acid decreased the L* value of extrudates from52.650.50 to 41.030.12, increased a* and b* values from 8.510.05 to 17.230.19 and 1.910.02 to 6.050.07, respectively.Although the addition of 2% citric acid increased the colour retentionfrom 41.770.66% to 63.240.38%, the extrudates was very sour andnot organoleptically acceptable. Therefore, 1% citric acid was useful,since it increased the retention of anthocyanin from 41.770.66%

to 59.970.46%. Kalt, McDonald, and Donner (2000) studied the

Table2

Effect

ofextrusionvariableson

bvaluea

andpe

rcen

tcolour

retention(%R)

aof

rice

extrud

ates

containing

pre-extrusionaddition

ofan

thocyanin.

Tem

(C)

14%moistureconten

t16

%moistureconten

t18

%moistureconten

t

Screw

speed(rpm

)

150

170

190

150

170

190

150

170

190

b%R

b%R

b%R

b%R

b%R

b%R

b%R

b%R

b%R

140

1.40

0.02

a36

.50

1.81

a1.56

0.06

a39

.36

0.43

a1.67

0.03

a39

.06

0.43

a1.07

0.02

a41

.75

0.25

a1.11

0.04

a42

.83

0.62

a1.15

0.03

a44

.58

0.80

a0.83

0.02

a52

.17

1.01

a0.90

0.03

a56

.25

0.66

a0.97

0.01

a56

.58

0.26

a

160

2.04

0.09

b30

.33

1.01

b2.01

0.19

b32

.38

1.01

b2.18

0.10

b34

.13

1.75

b1.86

0.02

b40

.88

0.14

b1.94

0.07

b40

.75

0.08

b1.91

0.02

b41

.77

0.66

b1.12

0.02

b45

.17

0.10

b1.18

0.04

b46

.91

0.50

b1.23

0.02

b47

.50

0.10

b

180

3.07

0.05

c26

.25

0.34

c3.35

0.09

c28

.58

1.01

c3.35

0.05

c25

.58

0.28

c2.06

0.02

c32

.08

0.67

c2.07

0.02

c35

.88

1.01

c2.18

0.03

c33

.83

0.21

c1.68

0.02

c42

.23

0.30

c1.74

0.07

c39

.83

1.15

c1.63

0.02

c41

.08

1.01

c

Means

withdifferen

tsupe

rscriptin

thesamecolumnaresign

icantly

differen

t(P

b0.05

).aRe

sultsarethemeanSD

ofthreede

term

inan

ts.

Table 3Sensory resultsa of pre-extrusion anthocyanin coloured rice extrudates.

Extrusionconditions

Appearance Colour Texture Overallacceptability

14 MC 140 C190 rpm

6.450.20a 6.550.28a 7.950.37a 6.900.41a

16 MC 140 C170 rpm

7.050.37b 8.000.50b 7.100.65b 7.350.22b

16 MC 160 C170 rpm

6.900.41ab 7.000.35a 7.500.50ab 7.050.37ab

16 MC 160 C190 rpm

8.100.41c 8.000.50b 7.500.35ab 8.000.35c

16 MC 180 C190 rpm

7.000.50b 7.450.44b 7.050.51c 7.000.50a

18 MC 140 C150 rpm

6.000.35d 6.550.44a 6.450.11c 6.500.61a

Means with different superscript in the same column are signicantly different(Pb0.05).

644 A.V. Durge et al. / Food Research International 50 (2013) 641646a Sensory score was the average of ten panel members using 9 point hedonic scale asfollows: 9like extremely, 8like very, 7like moderately much, 6like slightly,5neither like nor dislike, 4dislike slightly, 3dislike moderately, 2dislike verymuch, and 1dislike.

Table 4Effect of additives on colour and retentiona of anthocyanin in pre-extrusion colouredextrudates.

Additives L value a value b value % retention

Control 52.650.50a 8.510.05a 1.910.02a 41.770.66a

1% citric acid 46.770.15b 14.960.29b 3.480.02b 59.970.46b

2% citric acidb 41.030.12c 17.230.19c 6.050.07c 63.240.38c

1% NaHCO3 56.790.27d 7.180.14d 0.930.12d 24.750.43de e e estability of blueberry juice at pH 1, 4, and 7 found the stability ofanthocyanin to be 10-fold higher at pH 1 than at pH 4 and 7. The highlevel of anthocyanin at pH 1 is consistent with the presence of theavylium cation which is most intensely coloured, compared to thequinonoidal pseudobase, and chalcone forms which are pale orcolourless. Heredia, Francia-Aricha, Rivas-Gonzalo, Vicario, andSantos-Buelga (1998) also reported anthocyanins to undergo a lineardecease with increasing pH in red grape juice. Sodium bicarbonateincreased the L* value of the extrudates from 52.650.50 to 58.150.28, decreased the a* and b* values from 8.510.05 to 6.980.16and 1.910.02 to 0.810.09, respectively. Colour retention alsodecreased by almost 50% from 41.770.66% to 20.660.28%(Table 4).

2% NaHCO3 58.150.28 6.980.16 0.810.09 20.660.28

Means with different superscript in the same column are signicantly different(Pb0.05).

a Results are the meanSD of three determinations.b Product was not organoleptically acceptable.

Table 5Effect of addition of different levels of anthocyanin with 1% citric acid on retention ofanthocyanina in pre-extrusion coloured extrudates.

Additives Anthocyaninadded (%)

L value a value b value % retention ofanthocyanin

Control samplewithoutcitric acid

2 52.650.50

8.510.056

1.910.026

41.770.66

Controlwith1% citric acid

2 46.770.15

14.960.29

3.480.015

59.970.46

A 1 56.330.05

6.830.04

2.860.12

36.240.48

B 1.5 50.120.11

7.830.03

3.150.08

42.750.63

a Results are the meanSD of three determinations.

Citric acid has been recently reported to increase the retention ofanthocyanin in oven-baked cookies (Li, Walker, & Faubion, 2011).Since our study also showed citric acid to increase the retention ofanthocyanin in the extrudates, the percentage of colour to be added toget colour retention near to control sample without citric acid couldbe decreased on addition of 1% citric acid. Hence, trials wereconducted with 1.0% and 1.5% anthocyanin added with 1% citricacid. The sample with 1.5% addition of anthocyanin and 1% citric acidgave L*, a* and percent colour retention of 50.120.11, 7.830.03,and 42.750.08%, respectively (Table 5) which was quite close tocontrol. The exception was in terms of b* value which increased from1.910.02 (control sample) to 3.150.08 (1.5% colour and 1% citricacid sample). This could be due to the acidic condition of samplewhich lowered the blueness of sample, increased the stability ofanthocyanin. From this study, it can be concluded that addition of 1%citric acid decreased the requirement of the natural colourant by asignicant 25% without any change in the extrudate colour.

3.4. Storage study of anthocyanin-coloured extrudates

The anthocyanin-coloured extrudates prepared by adding 2.0%colourant (w/w) (without citric acid) were packed in LDPE and

metallized polyethylene, stored at ambient temperature (302 C),and evaluated in terms of L*, a*, b* and percent retention for 45 days(Fig. 1). Extrudates packed in LDPE showed an increase in L* value from51.840.25 to 58.420.12, a decrease in a* value from 8.210.13 to7.070.07, a decrease in b* value from 0.570.01 to 0.500.06, and adecrease in colour retention from45.580.23% to 38.240.17% duringthis period. In contrast, the samples packed in metallized polyethyleneshowed an increase in L* value from 51.840.25 to 52.930.02,indicating colour loss to be very low in this packaging material.

Extrudates packed in LDPE and metallized polyethylene storedunder light of 500 lx was studied for 28 days. The extrudates packedin LDPE showed an increase in L* value from 51.840.25 to 61.720.05, a decrease in a* value from 8.210.13 to 6.830.07 and b*value from 0.570.01 to 0.470.06, respectively. Again, in metal-lized polyethylene, the retention of anthocyanin was quite high(Fig. 2).

Fig. 3 shows a semi-log plot of percent retention of colour ofanthocyanin coloured extrudates packed in polyethylene and metal-lized polyethylene stored at ambient temperature. The linear natureof the graph indicated the decrease in percent retention of colour tofollow rst order kinetics. Skrede (1985) studied colour quality ofstored blackcurrant syrup and found the anthocyanin degradation to

A

B

A

B

645A.V. Durge et al. / Food Research International 50 (2013) 641646C

D

Fig. 1. Effect of packagingmaterial on A) L* value, B) a* value, C) b* value, andD) % colour

retention of anthocyanin coloured extrudates.C

D

Fig. 2. Effect of light on A) L* value, B) a* value, C) b* value, and D) % colour retention of

anthocyanin coloured extrudates.

follow rst order degradation kinetics during storage. Extrudatespacked in metallized polyethylene did not show any signicantchange in colour values, as well as colour retention of extrudates.

Fig. 3. Effect of packaging material on half life period of colour of anthocyanin colouredextrudates.

646 A.V. Durge et al. / Food Research IntHence, metallized polyethylene is suitable for packaging of anthocy-anin coloured extrudates. This is further clear from the half life (t1/2)of 148 and 770 days for 50% retention of colour in the extrudatespacked in polyethylene and metallized polyethylene, respectively.

Fig. 4 shows similar data for samples exposed to light of 500 lx. Asharp decrease in percent retention of colour was observed inextrudates packed in polyethylene, whilst that packed in metallizedpolyethylene showed very less decrease in percent retention. Thisstudy revealed the anthocyanin to be susceptible to light under thereported storage conditions. Polyethylene is not a good barrier tooxygen and light to which anthocyanin is sensitive, and is thereforenot suitable for packaging of anthocyanin coloured extrudates. Lightexposure of 500 lx showed a t1/2 of 43 and 408 days, respectively, inextrudates packed in polyethylene and metalized polyethylene,respectively. Sowbhagya, Smitha, Sampathu, Krishnamurthy, andBhattacharya (2005) reported natural colour curcumin to followrst order kinetics for colour retention during storage study of10 weeks in extruded product.

4. Conclusions

The retention of anthocyanin in rice extrudates that were colouredprior to extrusion increased with an increase in themoisture content offeed material, and screw speed and decreased with an increase in dietemperature. Addition of 1% citric acid increased retention of anthocy-anin by 20.34%, and sodium bicarbonates decreased its retention by50.53%. The content of colour to be added was reduced by 25% on

y = -0.0017x + 3.803 R = 0.9055

3.8

3.9y = -0.0163x + 3.7931 R = 0.9873

3.3

3.4

3.5

3.6

3.7

0 5 10 15 20 25 30

ln (%

Rete

ntion

)

Storage period (days)Polyethylene Metallized PE

Fig. 4. Effect of light on half life period of % colour of packed anthocyanin colouredextrudates.addition of 1.0% citric acid to rice our prior to extrusion. Packaging inmetallized polyethylene was suitable for packaging of anthocyanincoloured extrudates. Further studies on effect of metal and oxygenscavengers on anthocyanin coloured extrudates need to be studied.

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Stability of anthocyanins as pre-extrusion colouring of rice extrudates1. Introduction2. Materials and methods2.1. Materials2.2. Methods2.2.1. Preparation of sample2.2.2. Optimization of anthocyanin content in extruded rice flour2.2.3. Optimization of extrusion processing parameters2.2.4. Analysis of the coloured extrudates2.2.4.1. Colour measurement (Hunter L*, a* and b* values)2.2.4.2. Retention of anthocyanin colour2.2.4.3. Organoleptic evaluation of anthocyanin coloured extrudate

2.3. Effect of additives, packaging material and light on colour of retention in anthocyanin-coloured extrudates2.4. Statistical analysis

3. Results and discussion3.1. Optimization of content of anthocyanin for pre-extrusion of rice extrudates3.2. Optimization of extrusion processing parameter on anthocyanin retention3.2.1. Colour measurement3.2.2. Retention of anthocyanin in extrudates3.2.3. Organoleptic evaluation of anthocyanin-coloured extrudate3.2.4. Optimised conditions for extrusion

3.3. Effect of additives on colour of extrudates3.4. Storage study of anthocyanin-coloured extrudates

4. ConclusionsReferences