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International Journal of Food Properties

ISSN: 1094-2912 (Print) 1532-2386 (Online) Journal homepage: http://www.tandfonline.com/loi/ljfp20

Quality Characteristics and Glass TransitionTemperature of Hydrocolloid Pre-Treated FrozenPre-Cut Carrot

T. Maity , O. P. Chauhan , A. Shah , P. S. Raju & A. S. Bawa

To cite this article: T. Maity , O. P. Chauhan , A. Shah , P. S. Raju & A. S. Bawa (2011) QualityCharacteristics and Glass Transition Temperature of Hydrocolloid Pre-Treated Frozen Pre-CutCarrot, International Journal of Food Properties, 14:1, 17-28, DOI: 10.1080/10942910903118578

To link to this article: http://dx.doi.org/10.1080/10942910903118578

Published online: 13 Jun 2012.

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International Journal of Food Properties, 14:17–28, 2011Copyright © Taylor & Francis Group, LLCISSN: 1094-2912 print / 1532-2386 onlineDOI: 10.1080/10942910903118578

QUALITY CHARACTERISTICS AND GLASS TRANSITIONTEMPERATURE OF HYDROCOLLOID PRE-TREATEDFROZEN PRE-CUT CARROT

T. Maity, O.P. Chauhan, A. Shah, P.S. Raju,and A.S. BawaDefence Food Research Laboratory, Siddarthanagar, Mysore-570011, Karnataka,India

The effect of hydrocolloid pre-treatment, i.e., pectin, carboxy methyl cellulose, xanthan gumand sodium alginate on textural properties, drip losses and sensory quality as well as on glasstransition temperature (Tg

′ ′ ′) of the frozen-thawed pre-cut carrots was studied. Untreatedfrozen samples showed detrimental effects in texture and also excessive drip losses whilethe carrot tissue integrity was well retained in the hydrocolloid pre-treated samples. As theconcentration of the hydrocolloid increased, hardness and fracturability were also foundto increase. However, adhesiveness was observed to follow a reverse trend. Xanthan gum(0.4%) resulted in higher texture retention than other hydrocolloids used as well as thanthe control samples. Hydrocolloids imparted lightness and higher red and yellowness to thecarrot samples due to reduced solute mobility and moisture conditioning effects. Overallacceptability of the hydrocolloid pre-treated samples was found to be more than the experi-mental control samples. All the hydrocolloids were found to be effective in increasing theTg

′ ′ ′ to an extent, −2.73 to −0.28◦C compared with Tg′ ′ ′ (−5.4◦C) of untreated carrot

samples. Tg′ ′ ′ increased to almost 74% in CMC (0.4%) pre-treated samples. The maximum

enhancement was found in carboxy methyl cellulose followed by pectin, sodium alginate, andxanthan gum. The threshold concentrations in terms of sensory attributes were determinedfor optimal conditioning of the product prior to freezing.

Keywords: Carrot, Frozen, Texture, Hydrocolloids, Glass transition temperature.

INTRODUCTION

Frozen foods form an important aspect of processed foods due to several advantagesinclusive of retention of better sensory attributes such as flavor with minimal alterations inthe composition of heat sensitive vital nutrients. However, freezing and thawing of fruitsand vegetables can have deleterious effects on certain physical attributes, i.e., texture andexcessive soluble solid and water loss. When the water freezes it expands and the ice crys-tals cause the cell walls to rupture. When a frozen food is thawed for consumption, themoisture is readily separated from the matrix and it causes softening of the texture, driploss, and often deterioration of the overall quality.[1,2] The quality of frozen foods dependson a number of factors inclusive of size of the ice crystals, rapidity of freezing, and the typeof product as such.[3–5] Physicochemical conditioning of the product could be helpful in

Received 15 April 2009; accepted 15 June 2009.Address correspondence to T. Maity, Defence Food Research Laboratory, Siddarthanagar, Mysore-

570011, Karnataka, India. E-mail: tanumft@gmail.com

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18 MAITY ET AL.

retaining the overall quality in terms of texture and drip losses in addition to rapid freezingprotocols.

Hydrocolloids are high molecular weight polysaccharides used in various applica-tions in foods. They are known to render structural stability and also improve water holdingcapacity of foods.[6,7] Pectin is used in food industry to improve the dispersion, emul-sification, and stability of foods.[8] Carboxy methyl cellulose (CMC), a synthetic gumis a cellulose derivative and forms a three dimensional network with an ability to linkwater molecules within the system.[9] Xanthan gum hydrates in cold water because of thelarge side chains around the cellulose backbone. It is stable against freezing and thawingand exhibits resistance to a wide range of pH conditions. Alginates are high molecularweight salts of alginic acid with block structure, which gives them the ability to cross-linkand bind.[10] The control of water through the use of hydro dynamically active ingredi-ents is critical to maintaining texture and physical stability of the foods having relativelyhigh moisture contents.[11] Softening of texture as a result of cell wall rupture due tofreezing could be reduced by hydrocolloid pre-treatments. Hydrocolloids (xanthan, guar,carrageenan and pectin) and dairy proteins (sodium casienate and whey protein concen-trate) possess cryoprotectant properties.[12,13] Resistance to repeated-freezing and thawingin rice starch gel can be increased by using xanthan gum.[14] The effect of individualhydrocolloids and mixture of hydrocolloids and dairy proteins (sodium casienate and wheyprotein concentrate) were studied in frozen and thawed pureed cooked potatoes.[15,16]

Application of hydrocolloids is often followed to impart higher consistency in syrups[6]

and improve textural attributes of fruit leathers.[7]

Frozen food quality during storage largely depends on the storage temperature whichin turn is dependent on the glass transition temperatures (Tg

′′′) of the product beyond whichthe chemical reactivity is enhanced due to increase in solute mobility. The temperaturesassociated with the transformations of the unfrozen phase such as Tg

′′′ markedly affects thestability of the frozen product.[17] Glass transition temperatures are the common markersused to check the stability of the frozen products. The information of maximally freeze-concentrated glass defines the limit state for the unfrozen matrix in frozen systems.[18]

Chemical and physical stability of frozen foods depends on the molecular mobility of theunfrozen phase, which could be quantified as a function of Tg

′′′.[19] The higher the storagetemperature is above the Tg

′′′, the less viscous the unfrozen matrix becomes, allowing fasterdiffusion to occur.[20] As the storage temperature is increased above the Tg

′′′, the amountof unfrozen water mobilizing solutes in the viscous matrix increases. The increased mobil-ity of solutes allow enzymic and oxidation reactions to proceed and increases degradationin the product during frozen storage.[21] Modifications in the Tg

′′′ by use of hydrocolloidscould be helpful in reducing chemical reactivity and quality changes inclusive of oxidativedeterioration of vital nutrients such as carotenoids. Study of tri-stimulus color co-ordinatesas a response of hydrocolloid pre-treatment would help in having an objective measure-ment of quality changes in terms of changes in lightness, redness and yellowness of theproduct such as pre-cut carrots and the same in comparison with the Tg

′′′ profile wouldgive a comprehensive understanding of solute mobility, chemical reactivity and consequentcolor changes.

Several reports are available on the textural aspects and tissue integrity of frozencarrots illustrating the susceptibility of carrot tissue towards freezing and also heat treat-ments in the form of blanching. Prestamo et al.[22] described the histological changes interms of tissue disruption and also structural collapses in pectin, which is the cementinglayer between adjacent cells in frozen carrots. Fuchigami et al.[23] emphasized freezing as

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HYDROCOLLOID PRE-TREATMENT TO FROZEN PRE-CUT CARROT 19

a critical factor affecting the cell structure of carrots. Programmed freezing of carrots wasfound to minimize the size of ice-crystals thereby facilitating higher retention of quality.Therefore, there is a need to introduce a physicochemical conditioning in the form of pre-treatment such as hydrocolloids to minimize tissue damages during the freezing process.Commercial freezing often resorts to quick freezing by blast freezing methods by moder-ate blast velocities and pre-conditioning could help in minimizing the tissue damage andalso drip losses which are otherwise major problems associated with frozen carrots. In thepresent study, various food hydrocolloids (pectin, CMC, xanthan gum, and sodium algi-nate) were compared for their effects in reducing the drip losses, stabilizing the texture interms of hardness, adhesiveness, and fracturability with high sensory acceptability in thefrozen carrots. Glass Transition studies were also carried out.

MATERIALS AND METHODS

Materials

Raw carrots devoid of blemishes such as visible signs of microbial infections andphysical injuries were procured from the local market. Carrots after washing were peeledmanually and cut into longitudinal (30 × 10 × 10 mm), as well as transverse sections ina dicer (Urschel Laboratories, Inc., USA). Calcium chloride, pectin and carboxy methylcellulose (S. D. Fine Chemicals), xanthan gum (ICN Biomedical) and sodium alginate(Across) were procured as analytical grade chemicals.

Pre-Treatment

Diced carrots were blanched for 5 minutes at 70◦C in water. After blanching car-rots were dipped in 1% calcium chloride solution for two hours at room temperature(28 ± 2◦C). The calcium chloride treated samples were subjected to hydrocolloid dip treat-ment. Diced carrots (one part) were dipped in different hydrocolloid solutions (three parts)(pectin, CMC, xanthan gum and sodium alginate) at 0.2, 0.3, and 0.4% levels for 16 hoursat 5 ± 2◦C. After the dip period (16 h) hydrocolloid solution was drained and the surfacehydrocolloid was removed by washing in water (1:1, w/v) followed by draining. Treatedcarrot slices were packed and sealed in polyethylene bags (500 g each). The blanchedand calcium chloride treated samples without any hydrocolloid treatment served as theexperimental control.

Freezing and Thawing

Polyethylene bags containing carrot samples were frozen at −40◦C for 3 h at a blastvelocity of 8 m s−1 in a blast freezer (Cryoscientific, Bangalore) equipped with freezingrate controller. The frozen samples were stored in deep freezer at −20◦C for the instrumen-tal and sensory analysis. Thawing of the samples was carried at a temperature of 28 ± 1◦Cfor 30 min for the analytical work.

Instrumental Textural Measurements

Texture profile analysis (TPA) of frozen and thawed carrot samples was carriedout in four replications and the mean values were reported for hardness, fracturability,and adhesiveness. The measurements were taken using a texture analyzer (TAHDi, Stable

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20 MAITY ET AL.

Microsystems, London, UK) equipped with Texture Expert Software (Version 1.22; StableMicrosystems, London, UK). Samples were compressed with a load cell of 5 kg with 0.01precision using a spherical probe of 75 mm diameter at a cross head speed of 1 mm/s to afixed distance of 25 mm, withdrawn to the original sample height allowing the sample torecover during a fixed rest period of 5 seconds and repeating the original compression toprecisely the same distance as the original penetration. The software automatically calcu-lated the textural parameters as follows: hardness (N) is given either as the first force peakwhen there are two peaks on the TPA curve or by the second peak if there are three peaks.Adhesiveness (Nm) is the negative area between the point at which the first curve reacheda zero force value after the first compression and the start of the second curve.

Centrifugal Drip Losses

Centrifugal drip loss was measured by modifying the procedure given byDowney.[16] Approximately 3 g of sample was weighed into a paper thimble before cen-trifugation (MPW-350R, Med. Instruments, Poland) at 25◦C at the rpm of 5000 g for10 min. The content after centrifugation was taken out of the paper thimble, weighed andaverage centrifugal drip loss was reported on percentage basis. Samples were analyzed infour replicates.

Color Analysis

Frozen samples were allowed to equilibrate at room temperature (∼28◦C) for 30 min.The mean CIE L∗, a∗, and b∗ values of surface of carrot samples were recorded using acolorimeter (Miniscan XE plus, Model No. 45/0-S, Hunter Associates Laboratory, Inc.,Reston, VA, USA) which was calibrated using white and black standard ceramic tiles. Thereadings were taken using D-65 illuminant and 10O observer. Samples were analyzed infour replicates.

Glass Transition Studies

Thermal properties of carrot samples in terms of Glass Transitions were analyzedusing DSC-2010 (TA Instruments, USA) equipped with a thermal analysis data station(TA Universal Analysis, Version 3.0). Samples (not more than 20 mg, wb) were weighedinto an aluminum pan (900796.901, Du Pont, Wilmington, DE). The experimental tem-perature range was from −60 to 20◦C which rises at the rate of 10◦C/min. Samples werehermetically sealed and loaded into the DSC and cooled to −60◦C and held at that tem-perature for about 5 minutes before being scanned over the temperature range set above.The DSC analyzer was calibrated using indium and an empty aluminum pan was used asreference. Thermal properties such as onset temperature (To); peak temperature (Tp), andglass transition temperature (Tg

′′′) were calculated from DSC thermograms.[24] Sampleswere analyzed in three replicates.

Sensory Analysis

Frozen-thawed carrot samples were served to a 10 trained member panel for sensoryevaluation in terms of overall acceptability using a nine point hedonic scale.[25] Panelistswere scientific staffs of the laboratory who were trained in the use of attributing rating scale

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HYDROCOLLOID PRE-TREATMENT TO FROZEN PRE-CUT CARROT 21

for the characteristics examined. The scores were assigned from extremely liked (9) to dis-liked extremely (1). The samples were served to the panelists after coding with three digitsrandomly selected numbers in a sensory lab illuminated with white light and maintainedat 20◦C.

Statistical Analysis

Statistical analysis was performed by analysis of variance (ANOVA) and means werecompared using the least significant difference (LSD, 95%) by Duncan’s multiple rangetests using Statistica 7 software (StatSoft, Tulsa, Oklahama, USA).

RESULTS AND DISCUSSION

Textural Parameters

The hardness, fracturability, and adhesiveness from texture profile analysis (TPA) ofthe hydrocolloid pre-treated frozen-thawed carrot samples cut transversally as well as lon-gitudinally are presented in Table 1. Hydrocolloid pre-treatment significantly (P < 0.05)affected all the textural parameters. In case of longitudinally cut samples, a value of0.838 ± 0.04 N for hardness, 0.075 ± 0.015 N for fracturability and 0.992 ± 0.005 Nmfor adhesiveness was recorded in the experimental control samples through the TPA anal-ysis. As the concentration of hydrocolloids increased, hardness values were also found toincrease. The hardness of pectin, CMC, xanthan and sodium alginate treated longitudinallycut samples ranged from 1.26 to 1.80 N, 1.42 to 2.07 N, 1.59 to 2.61 N, and 1.33 to 1.85 N,respectively. Similarly the hardness of pectin, CMC, xanthan and sodium alginate treatedtransversally cut samples ranged from 1.41 to 1.96 N, 1.53 to 2.22 N, 1.73 to 2.74 N, and1.49 to 2.25 N, respectively. Xanthan (0.4%) showed maximum increase in hardness fromthe control followed by CMC, sodium alginate and pectin, respectively in both the sam-ples. The increased hardness of the hydrocolloid pre-treated samples might be due to theproperty of hydrocolloids to bind water and prevent excessive moisture loss during freez-ing and thawing. Increasing hydrocolloid concentration was accompanied by decrease inadhesiveness values. Xanthan gum showed maximum reduction in adhesiveness valuesfollowed by pectin, sodium alginate and carboxy methyl cellulose. An increase of fractura-bility in longitudinally and transversally cut carrot samples was found due to hydrocolloidpre-treatment. But the increase was statistically insignificant (P > 0.05) over the controlas well as among the hydrocolloids. Though the increase in fracturability was not muchsignificantly (P > 0.05) different from the control, xanthan gum showed higher values fol-lowed by pectin, sodium alginate and CMC. Overall, higher textural values were recordedin transversally cut carrot samples in terms of hardness and fracturability. Significant(P < 0.05) differences in hardness and adhesiveness were recorded for different hydro-colloids pretreated samples of transversally and longitudinally cut carrot samples. Higherconcentration of hydrocolloids imparted significant differences on fracturability however;it was non-significantly affected by mode of cutting the samples.

Reduction in the deterioration of food products due to freezing by using hydrocol-loids have been reported by several authors. Deteriorating effect from freezing in wheatflour and corn flour pastes can be reduced by xanthan.[26] The retention of texture asobserved by increased textural parameters over the experimental control could be due tointeraction of the hydrocolloids with water. According to Lee et al.[27] the hydrodynamic

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Tabl

e1

Eff

ecto

fdi

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enth

ydro

collo

idpr

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eatm

ents

onin

stru

men

talt

extu

repa

ram

eter

sof

froz

en-t

haw

edpr

e-cu

tcar

rot(

n=

4).

Har

dnes

s(N

)Fr

actu

rabi

lity

(N)

Adh

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m)

Tre

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Lon

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Tra

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dina

lT

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e

Pect

in0.

21.

26±

0.03

b1.

41±

0.02

c0.

094±

0.01

4a0.

102±

0.00

3a0.

872±

0.00

5b0.

810±

0.00

6b

0.3

1.43

±0.

04c

1.59

±0.

08d

0.10

8±

0.00

9a0.

113±

0.00

2a0.

789±

0.01

1c0.

740±

0.00

6c

0.4

1.80

±0.

03e

1.96

±0.

04e

0.11

4±

0.01

3b0.

121±

0.01

1b0.

700±

0.01

4d0.

688±

0.00

9d

CM

C0.

21.

42±

0.08

c1.

53±

0.11

cd0.

085±

0.01

6a0.

095±

0.01

6a0.

911±

0.00

8a0.

887±

0.00

7b

0.3

1.60

±0.

05d

1.73

±0.

04d

0.09

5±

0.00

7a0.

105±

0.00

8a0.

827±

0.00

5b0.

788±

0.00

5c

0.4

2.07

±0.

13e

2.22

±0.

14f

0.10

7±

0.01

8a0.

117±

0.00

6b0.

749±

0.00

3c0.

639±

0.00

8d

Xan

than

Gum

0.2

1.59

±0.

03d

1.73

±0.

13d

0.07

4±

0.00

5a0.

090±

0.01

3a0.

800±

0.01

1bc0.

767±

0.01

2c

0.3

1.88

±0.

11e

2.03

±0.

07d

0.12

3±

0.00

8b0.

131±

0.01

4b0.

691±

0.00

8d0.

668±

0.01

2d

0.4

2.61

±0.

06g

2.74

±0.

08g

0.13

3±

0.01

0b0.

141±

0.00

3b0.

588±

0.01

3e0.

570±

0.00

7e

Sodi

umA

lgin

ate

0.2

1.33

±0.

04bc

1.49

±0.

13c

0.08

9±

0.01

4a0.

103±

0.00

8a0.

936±

0.01

2a0.

879±

0.01

1b

0.3

1.55

±0.

12cd

1.78

±0.

02d

0.08

6±

0.00

9a0.

117±

0.00

8b0.

828±

0.00

4b0.

823±

0.01

5b

0.4

1.85

±0.

07e

2.25

±0.

15f

0.11

7±

0.01

8b0.

127±

0.00

5b0.

755±

0.00

6d0.

726±

0.01

1c

Con

trol

0.84

±0.

04a

1.10

±0.

17a

0.07

5±

0.01

5a0.

088±

0.00

3a0.

975±

0.00

5a0.

962±

0.00

9a

Val

ues

with

diff

eren

tsup

ersc

ript

sin

the

sam

eco

lum

ndi

ffer

sign

ifica

ntly

.Lea

stsi

gnifi

cant

diff

eren

ce(P

<0.

05).

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HYDROCOLLOID PRE-TREATMENT TO FROZEN PRE-CUT CARROT 23

properties of hydrocolloids is due to water binding and its distribution between particulatesand matrix. In the present study xanthan gum was found to improve textural attributes inpre-cut carrot in frozen condition. However, the threshold values of xanthan gum at 0.3%concentration in terms of sensory scores discussed elsewhere need to be followed and thetextural attributes showed significant improvement at 0.3% hydrocolloid concentration.

Drip Loss

Thawing of frozen products results in drip losses in which soluble solids leachesout along with water. Effect of different hydrocolloid pre-treatments on the retention ofdrip losses are predicted in Fig. 1. A maximum drip loss of 66.69% was observed in thecontrol samples while; all the hydrocolloids were found to decrease the drip losses signifi-cantly (P < 0.05). Xanthan gum was more effective in decreasing the drip losses followedby pectin, CMC and sodium alginate, respectively. Pre-treatment of carrots in 0.4% xan-than gum showed maximum reduction in drip losses. It could reduce the drip losses up to34.97%. The drip loss in xanthan pre-treated samples were found to be 48.69, 47.28, and43.37% at 0.2, 0.3, and 0.4%, respectively. Drip losses in pectin pre-treated samples at 0.2,0.3 and 0.4% were 52.94, 48.04, and 47.58%, respectively. Drip losses associated with 0.2,0.3 and 0.4% CMC and alginate pre-treatments were also significant (P < 0.05) over theexperimental control with values 53.55, 51.08, and 47.98% and 55.28, 52.49, and 49.64%,respectively. Reduction in drip losses of the hydrocolloid pre-treated samples could beattributed to the water-binding properties of the hydrocolloids.

Color Measurements

Changes in CIE color values in terms of L∗, a∗, and b∗ values are recorded inTable 2. Color value was found to increase as compared to control with the increase inthe concentration of different hydrocolloids in terms of L, indices. The effect of increased

Figure 1 Effect of different hydrocolloid pre-treatments on drip losses of frozen-thawed pre-cut carrot.(P < 0.05).

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24 MAITY ET AL.

Table 2 Instrumental color values and overall acceptability of the hydrocolloid pre-treated frozen-thawed pre-cutcarrot (n = 4, nx = 10).

Levels L∗ a∗ b∗ OAAx

Pectin 0.2 48.73 ± 0.06d 29.38 ± 0.03d 32.28 ± 0.05a 6.63 ± 0.07b

0.3 49.31 ± 0.04b 28.71 ± 0.02c 35.41 ± 0.02b 6.86 ± 0.08c

0.4 50.42 ± 0.03e 23.36 ± 0.03b 38.35 ± 0.01d 7.41 ± 0.06d

CMC 0.2 44.39 ± 0.02b 29.36 ± 0.01d 33.53 ± 0.01a 6.19 ± 0.03a

0.3 46.17 ± 0.03c 25.46 ± 0.03b 35.81 ± 0.03b 6.38 ± 0.08b

0.4 48.67 ± 0.01d 24.17 ± 0.02b 38.28 ± 0.01d 7.10 ± 0.06d

Xanthan 0.2 42.25 ± 0.02a 28.19 ± 0.01c 33.11 ± 0.02a 7.22 ± 0.05d

0.3 44.86 ± 0.03b 25.59 ± 0.02b 35.65 ± 0.02b 7.85 ± 0.03f

0.4 49.55 ± 0.05e 23.99 ± 0.02b 37.06 ± 0.01c 6.26 ± 0.04a

Sodium Alginate 0.2 42.12 ± 0.03a 28.44 ± 0.03i 33.48 ± 0.04a 7.57 ± 0.03e

0.3 44.90 ± 0.01b 27.34 ± 0.01c 36.25 ± 0.02b 7.52 ± 0.02e

0.4 47.39 ± 0.04c 24.81 ± 0.02b 38.81 ± 0.03d 6.86 ± 0.03c

Control 42.98 ± 0.02a 17.23 ± 0.02a 30.74 ± 0.01a 5.86 ± 0.03a

Values with different superscripts in the same column differ significantly. Least significant difference(P < 0.05).

hydrocolloid concentration on color was found to be most pronounced with respect topectin followed by CMC, xanthan and sodium alginate, respectively. The increase in light-ness could be attributed to the moisture conditioning effect of hydrocolloids. The rednessof the samples decreased as the concentration of hydrocolloids increased. However, therecorded a∗ values for the hydrocolloid pre-treated samples were higher than the controlsamples. The changes in a∗ values were maximum in Pectin. The reduction in redness of thecarrot samples might be due to the lightening effect of the hydrocolloids. The yellownesswas found to follow similar trend like L values. Yellowness (b∗ values) of the carrot sam-ples increased due to the hydrocolloid pre-treatment. Visual appearance of xanthan andalginate pre-treated samples were more appealing than the pectin and CMC pre-treatedsamples due to less changes in the color values. The color stabilization in terms of L∗,a∗, and b∗ values could be attributed to increase in the Tg

′′′ values of the product causingrestriction in solute mobility and chemical reactivity. These aspects could result in sta-bilization of carotenoids with restriction in oxidation. Lim et al.[21] reported a profoundinfluence of Tg

′′′ on oxidation susceptible constituents such as chlorophyll and ascorbicacid. However, the effects of Tg

′′′ on individual color entity specific and anthocyanins werereported to be less dependent on Tg

′′′ values during freezing and subsequent storage.[18]

In the present study the changes seen in L∗, a∗, and b∗ values show a significant deviationfrom the control samples highlighting more lightness, redness and yellowness which couldbe attributed to moisture conditioning and carotenoids stabilization during the freezing andthawing processes.

Sensory Acceptability

Table 2 shows average values of sensory preference of hydrocolloid pre-treatedfrozen- thawed pre-cut carrot samples, as well as of the experimental control samplesin terms of overall acceptability (OAA). The hydrocolloid pre-treatment significantly(P < 0.05) affected the OAA. Increase in pectin and CMC concentrations from 0.2 to0.4% was accompanied by increase in the OAA as compared to the experimental control.Xanthan pre-treatments affected the OAA differently. Different concentrations exhibited

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HYDROCOLLOID PRE-TREATMENT TO FROZEN PRE-CUT CARROT 25

different affects on OAA. Increasing the gum concentrations resulted in increased sensoryscores. This could be due to the ability of the hydrocolloid to bind water within the carrottissue, which in turn improved structural integrity and resulted in higher sensory scoresthan the control. But, when excess xanthan (0.4%) was used, however the tendency of gumto impart thickening could cause the adverse effect. As a result, 0.4% xanthan pre-treatmentshowed lower sensory scores. As the concentration of sodium alginate increased the sen-sory scores also decreased. The sensory acceptability of 0.2% alginate was more than theother two concentrations this might be due to the block structure of alginate, which gavethe product inferior appearance, chewiness, and taste and resulted in lower OAA.

Thermal Properties

Tg′′′ of the carrot samples was analyzed after removing the surface moisture on the

samples using partial air drying. The thermograms indicating the Tg′′′ of the carrot samples

pre-treated with different hydrocolloids at 0.2, 0.3, and 0.4% levels are shown in Fig. 2. Allthe hydrocolloids were found to increase the Tg

′′′ significantly (P < 0.05). Tg′′′ was also

found to increase with increasing concentrations. Rizzolo et al.[28] reported that additionof carbohydrates such as maltose could shift the Glass transition to higher temperatures infrozen blueberry juices. Lim et al.[21] compared the Tg

′′′ of tender and old peas and reported

a b

c d

Figure 2 DSC thermograms showing glass transition temperatures (Tg′′ ′) of the carrot samples pre-treated with

(a) CMC, (b) Pectin, (c) Sodium Alginate, and (d) Xanthan gum. (Figure provided in color online.)

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26 MAITY ET AL.

Table 3 Glass transition temperatures (Tg′′ ′), Onset temperature (To) and Peak temperatures (Tp) of the

hydrocolloid pre-treated frozen-thawed pre-cut carrot (n = 3).

Levels Tg′′ ′ (◦C) To (◦C) Tp (◦C)

Pectin 0.2 −1.41 ± 0.03c −3.69 ± 0.14d 8.87 ± 0.10b

0.3 −1.05 ± 0.02d −3.20 ± 0.05c 10.64 ± 0.04c

0.4 −0.63 ± 0.06e −3.05 ± 0.12c 12.06 ± 0.07d

CMC 0.2 −1.50 ± 0.05c −4.12 ± 0.04e 10.39 ± 0.03c

0.3 −0.98 ± 0.06d −4.22 ± 0.06e 11.24 ± 0.02d

0.4 −0.28 ± 0.13f −4.51 ± 0.09f 12.61 ± 0.05e

Xanthan 0.2 −2.60 ± 0.09b −2.82 ± 0.08b 8.54 ± 0.02a

0.3 −2.17 ± 0.12b −2.74 ± 0.03ab 9.12 ± 0.04b

0.4 −1.39 ± 0.04c −2.68 ± 0.02a 10.24 ± 0.04c

Sodium Alginate 0.2 −2.73 ± 0.07b −3.29 ± 0.10c 9.04 ± 0.05b

0.3 −1.74 ± 0.12c −3.12 ± 0.03c 10.23 ± 0.03c

0.4 −1.28 ± 0.08c −2.92 ± 0.04b 11.24 ± 0.02d

Control −5.40 ± 0.23a −2.41 ± 0.05a 8.36 ± 0.08a

Values with different superscripts in the same column differ significantly. Least significant difference(P < 0.05).

that higher Tg′′′ values in old peas was due to higher amount of starch content than the ten-

der peas. CMC pre-treatment showed higher increase in the Tg′′′ values followed by pectin,

sodium alginate and xanthan as compared to experimental control. The onset tempera-ture, peak temperature and glass transition temperature are shown in Table 3. Maximumincrease in Tg

′′′ (74%) was observed in the samples pre-treated with 0.4% level of CMC.The glass transition temperature shifted from −5.4◦C of control carrot samples to −1.50,−0.99, and −0.28 in carrot samples pre-treated with CMC at 0.2, 0.3 and 0.4% levels,respectively (Table 3). Increase in Tg

′′′ associated with 0.2, 0.3, and 0.4% pectin, alginateand xanthan pre-treatments were also significant over the experimental control with val-ues −1.41, −1.05, and −0.63; −2.73, −1.74, and −1.28, and −2.60, −2.17, and −1.39◦C,respectively.

In the present study it is highlighted that pre-treatment with hydrocolloids is as sucheffective in terms of improvement in textural profile without softening and excessive driplosses. The enhancement in Tg

′′′ values could not only result in color stabilization but alsoin enhancement of requisite storage temperature which needs to be equal to or lesser thanthe Tg

′′′. However, the sensory scores need to be the markers in establishment of maximumlevels for commercial usage. The pre-treatment with hydrocolloids is as such cost effectiveand could be used in combination with quick freezing techniques to maximize the qualityattributes of frozen carrots in pre-cut form.

CONCLUSIONS

Textural parameters of hydrocolloid pre-treated samples were significantly higherthan the respective non-treated samples when measured after thawing. This indicated aprotective effect of hydrocolloids on cell integrity, which is altered during the freezingprocess. Xanthan gum (0.4%) concentration showed best results in terms of mechanicaltexture. Mode of cutting significantly affected the textural properties in terms of hardnessand adhesiveness of pre-cut carrot treated with different levels of various hydrocolloids.Sensory acceptability of pre-cut frozen carrot also increased due to hydrocolloid treatment.

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HYDROCOLLOID PRE-TREATMENT TO FROZEN PRE-CUT CARROT 27

Acceptability of xanthan gum pre-treated product at 0.3% concentration was observedmaximum compared with other hydrocolloids. It can be concluded that all selected hydro-colloids (pectin, CMC, xanthan gum and alginate) were useful in reducing the drip losses,improving the texture as well as sensory acceptability to different extents. Tg

′′′ was alsofound to increase with increasing concentrations of hydrocolloid with the effect being morepronounced with CMC followed by pectin, sodium alginate and xanthan gum as comparedto control samples in untreated frozen and thawed condition.

ACKNOWLEDGMENT

The valuable suggestions by Dr. Alok Saxena during manuscript preparation are gratefullyacknowledged.

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