kinetics of hmf formation during storage of instant kheer mix powder and development of a shelf-life...

KINETICS OF HMF FORMATION DURING STORAGE OF INSTANTKHEER MIX POWDER AND DEVELOPMENT OF A SHELF-LIFEPREDICTION MODELjfpp_754 1..11

ALOK JHA1,3 and ASHOK AMBALAL PATEL2

1Department of AH & Dairying, Banaras Hindu University, Varanasi 221 005, India2Dairy Technology Division, National Dairy Research Institute, Karnal 132 001, India

3Corresponding author.TEL: 91-542-2369646; FAX: 91-542-2368993;EMAIL: [email protected]

Accepted for Publication April 14, 2012

doi:10.1111/j.1745-4549.2012.00754.x

ABSTRACT

Kheer is one of the most widely consumed traditional dairy products of SoutheastAsian nations including India. Because of its poor shelf life, which hinders its com-mercialization and large-scale industrial production, product is confined to domes-tic kitchens and small-scale manufacturers. A shelf-stable dry mix was produced byusing spray-drying technology with an aim to develop a convenient formulation forthe traditional kheer. Instant kheer mix (IKM) powder could be easily reconstitutedinto kheer. The shelf life of IKM powder stored at 30, 37 and 45C was determined.Various physicochemical changes in kheer mix powder were monitored duringstorage and their effects on sensory properties of reconstituted kheer were studiedand correlated. The change in color of IKM powder was found to be a zero-orderreaction. The activation energy (Ea), Arrhenius constant and Q10 value for the reac-tion were 106.50 kJ/mol, 9.846 ¥ 1,017 M/wk and 3.8, respectively. The total and freehydroxymethylfurfural (HMF) formation during storage was found to increase andsensory scores found to decrease during storage. In fresh kheer mix powder,the average value recorded was 5.0 mmol/L, which increased to 21.74 mmol/L after 24weeks of storage at 30C. At 37 and 45C, the total HMF content increased to 30.4and 56.3 mmol/L after respective storage durations of 16 and 8 weeks. These changescould be described well with first-order reaction kinetics. The rates of these reac-tions were highly temperature-dependent, the rates being higher at high tempera-ture. The Ea and other activation parameters such as enthalpy, entropy and freeenergy of activation for these reactions were determined. The interrelationshipsbetween sensory and HMF changes were established. The sensory color was nega-tively correlated with absorbance and also with increase in HMF values. The shelf-life prediction model, which was developed based on the kinetic constants and therelationship between sensory and chemical parameters, could be useful in predictingthe shelf life of kheer mix powder. Potential shelf life of kheer mix powder was foundto be 92 weeks at 37C, which is comparable with most spray-dried powders.

PRACTICAL APPLICATIONS

About 50% of the milk produced in India (117.0 million tons) is converted intotraditional dairy foods. Traditional dairy foods include cereal-based dairy desserts,which are confined to domestic kitchens because of lack of technological processesfor their large-scale manufacture. Packaging of these products is almost nonexistent.Market for such products is estimated to be about INR 50,000 crore (US$ 10.29billion). Most of these products are consumed locally as they suffer from poor shelflife. Recent focus is on developing new and innovative processes for convertingthese traditional dairy foods into convenient formulations so that shelf life isenhanced and there is an ease of consumption. Development of a spray-driedprocess for large-scale manufacture of instant kheer mix with a potential shelf lifeof more than 92 weeks at ambient temperature could result in product diversifica-tion, export promotion and value addition for the food and dairy industry.

Journal of Food Processing and Preservation ISSN 1745-4549

1Journal of Food Processing and Preservation •• (2012) ••–•• © 2012 Wiley Periodicals, Inc.

INTRODUCTION

As a result of increasing urbanization, consumption of milkproducts more and more in convenient forms is on anincrease worldwide and also in India. Consumers also placean increasing emphasis on the safety, quality and nutritionalvalue of the foods they consume (Franzen et al. 1990). Kheeris one of the most significant traditional dairy products ofSoutheast Asian nations including that of India. It is a milk-based dessert comprising of rice grains gelatinized whilecooking for about 45 min and sugar is added to it while thecooking of rice is in progression. At the end of cooking, milkgets concentrated as a result of oozing of rice starch in it andalso because of evaporation of moisture (Aneja 1997). It isconventionally manufactured at domestic and cottage scalewith a poor technology base. As a result, it has a poor shelflife of 2–3 days even under refrigeration. Conventional kheeris sold in the local market without any appreciable packaging.Though normally, connotation of kheer means a milk-rice-based product, several variations in kheer includes productsbased on wheat (dalia), semolina, pearl millet, makhana, etc.Conventional process for manufacturing each of these varia-tions is almost similar except for the raw material being used.Because of the problems and limitations of traditional dairyfoods discussed above, these products have not been com-mercialized and manufactured on a large scale. Today, large-scale production, consumption and utilization of newer foodproducts with added convenience, better shelf life and attrac-tive packaging is gaining market. Several traditional foodshaving poor shelf life can be converted into powdered formfor enhanced shelf life and improved commercial value.Powdered foods need to be analyzed for their shelf life anddeteriorative changes during storage.

Hydroxymethylfurfural (HMF) is formed upon heattreatment of milk and milk-resembling systems by the Mail-lard reaction, via its Amadori product lactulosyl-lysine,as well as by isomerization and subsequent degradation ofsugars (Morales et al. 1998; Van Boekel 1998). Change infood color is associated with heat treatment of the food(Seonggyun and Bhowmik 1995). During the storage ofdairy products, the nutritive value and quality undergoesmajor changes as a result of Maillard reaction (Tekinsen andGuerbuez 1994). Indirectly heated milk in ultra-high tem-perature (UHT) was stored at 22 and 37C to study theeffects of some factors on Maillard browning, which leadsto stale flavor and bitter taste formation during storage(Adhikari and Singhal 1991). It was found that free HMFcontent increased from 2.91 to 7.85 and 7.04 mmol/L, andtotal HMF content from 7.87 to 26.77 and 21.8 mmol/L at37 and 22C, respectively, after 33 days of storage. Le et al.(2011a,b) found correlation between the Maillard reactionand solubility loss in modified milk protein concentrate(MPC) to which glucose was added to enhance the rate of

the Maillard reaction. They studied the Maillard reaction bymeasuring furosine and free HMF contents by high perfor-mance liquid chromatography. They reported that furosine,free HMF and browning in MPC increased during storage,whereas the solubility decreased. Protein changes in relationto solubility, Maillard reaction and protein cross-linking inwhole milk powder (WMP), skim milk powder (SMP), andwhey protein concentrate (WPC) stored at different relativehumidity (RH) were investigated by chemical and electro-phoretic methods (Le et al. 2011a,b). They observed thatthe loss of solubility corresponded with the developmentof high-molecular-weight protein complexes. The maximalMaillard reaction rate occurred at 66% RH for WMP andSMP, and 84% RH for WPC based on the furosine andHMF contents. Kinetics of color development (fromMaillard-type browning reactions) at high temperaturewere studied in aqueous solutions containing glucose andglycine, as well as a combination of these with ascorbic acidand thiamin and it was indicated that color developmentcould be described by first-order kinetics (Ghazala et al.1991). Individual and combined effects of different factors(e.g., pH, temperature of storage and heating time) on theMaillard browning reaction have also been studied usingresponse surface methodology (Anese et al. 1998; Bates et al.1998). Free HMF formation in milk has been found to bepromoted by the presence of higher fat content (Moraleset al. 1999). Free and total HMF in powdered infantformulae during storage at 55C increased in a nitrogenatmosphere. The 90-day storage in a nitrogen atmosphereproduced more than eight times the free HMF than thatproduced under oxygen (Guerra-Hernandez et al. 2002).Reddy et al. (1999) studied the kinetics of HMF formationin UHT milk and found that HMF formation was bestdescribed by a simple zero-order reaction with activationenergy (Ea) values of 121.68 and 108.70 kJ/mol for directand indirect heating, respectively. Q10 values were 2.38and 2.17 for direct and indirect heating, respectively. Theprogress of the Maillard reaction in dried infant formulawas monitored for 9 months of storage at 20, 30 and 37C.HMF content increased at all the temperatures of storageand based on this increase, an equation was derived topredict the shelf life of such products (Albala-Hurtado et al.1998). A mathematical model describing the kinetics ofcolor changes during hazelnut roasting was developed,which was also temperature dependent (Ozdemir andDevres 2000). Kinetics of color changes promoted byheat-induced browning in WMP comprising sucrose werestudied by Pauletti et al. (1999) and was found to followfirst-order reaction. Nonenzymatic browning in cheddarcheese powder during storage in the range of 20–40C wasfound to follow zero-order reaction kinetics with Ea and Q10

values being in the range of 15.1–22.3 kcal/mol and 2.2–3.5,respectively (Kilic et al. 1997). Similarly, in another study,

SHELF LIFE OF KHEER MIX POWDER A. JHA and A.A. PATEL

2 Journal of Food Processing and Preservation •• (2012) ••–•• © 2012 Wiley Periodicals, Inc.

it was reported that change in color of mango powderduring storage follows first-order reaction kinetics (Jaya andDas 2005). Kesseler and Fink (1986) obtained similar resultsfor color changes in sterilized milk stored at atmosphericconditions. Also, the concentrated tomato paste duringthermal treatments, which underwent color changes, fol-lowed first-order reaction kinetics (Barreiro et al. 1997).

Heat-induced changes in soymilk and sensory color esti-mation was reported by Kwok et al. (1999). It was concludedthat Commission Internationale de l’ Eclairage Lab valuescould be successfully applied to soymilk to characterizeheat-induced browning reactions and can be used as indica-tors of severity of heat treatments. Reciprocal of percentagereflectance at 450 nm increased following a first-order reac-tion. Kinetics of color degradation in prickly pear juices andjuice concentrates when stored at different temperatures fordifferent periods of time were studied by Saenz et al. (1993).A mathematical model was developed based on the data ofcolor change, which could predict the shelf life of theseproducts as a function of time and temperature of storage.Color changes in three different milk-cereal-based infantfoods were measured after storage at 25, 30 and 37C for 9months and it was reported that there was an increase incolor and fluorescence, the values being greater at 37C thanat 30 and 25C (Bosch et al. 2007).

A technological process was developed for large-scalemanufacture of spray-dried kheer mix powder (Jha et al.2002), which could be reconstituted to conventional kheer,thereby providing convenience to consumers. In the presentwork, spray-dried kheer mix powder was stored at three dif-ferent temperatures for studying the kinetic changes duringstorage on the basis of HMF formation and for develop-ing models for predicting its shelf life under acceleratedstorage conditions. The interrelationship between sensoryand HMF changes were established. The shelf-life predic-tion model, which was developed based on the kinetic con-stants and the relationship between sensory and chemicalparameters, could be useful in predicting the shelf life ofspray-dried kheer mix powder. The findings of the presentwork could help not only in the prediction of the shelf lifeof dry kheer mix powder and would also be useful for deter-mining the shelf life of several other dried foods, which arespecially relevant to tropical countries.

MATERIALS AND METHODS

Materials

Instant kheer mix (IKM) powder was manufactured accord-ing to the procedure given by Jha et al. (2002). Samples ofkheer mix powder (250 g) packaged in low-density polyethyl-ene pouches (Amtech Packaging, Mysore, India) were storedimmediately at 30, 37 and 45C in thermostatically controlled

cabinets (M/S Narang Co., New Delhi, India) to study theshelf-life parameters. The powder contained, on an average,1.91% moisture, 18.22% fat, 15.31% protein, 2.51% ash and62.71% carbohydrates (including sucrose). Samples werewithdrawn from storage at regular intervals, i.e. after every4 weeks at 30C, fortnightly at 37C, and every week at 45C,the storage period being 24, 16 and 8 weeks, respectively.

Reconstitution of Dried KheerMix into Kheer

Spray-dried kheer mix powder was packaged separately andinstant rice grains were packaged separately in a small poly-ethylene pouch. Once the pouch containing both the com-ponents was opened, instant rice grains were removed firstand put in the boiling water, which took 10 min for ricegrains to fully cook. Then, dried kheer mix was dispersed inthe rice–water mixture and mixed. Reconstituted kheercould be consumed hot or allowed to cool before serving.

Sensory Evaluation of Reconstituted Kheer

Sensory evaluation of reconstituted kheer was performedby a panel of nine semi-trained judges from the faculty ofthe Dairy Technology Division, National Dairy ResearchInstitute, Karnal, India. A special laboratory with necessaryfacilities viz., separate booths, provisions for adequate dif-fused light and air-conditioned odor-free environment wasemployed for product evaluation. Reconstituted kheer wasserved at 25C and RH of 60% was maintained. Hedonicrating (9-point scale; 1 = disliked extremely and 9 = likedextremely) was used for color, texture, flavor and overallacceptability of the conventional as well as reconstitutedkheer. A proforma was also devised for texture profile analy-sis, degree of brown discoloration and intensity of off-flavorattributes (10-cm long structured linear 100 points intensityrating scale). Sensory evaluation of reconstituted kheer wasdone by the procedure given by Jha et al. (2002).

Regression Analysis

Sensory and physicochemical data were subjected to corre-lation and regression analysis employing standard statisticalmethods (O’ Mahony 1986).

Measurement of Color in Terms ofReflectance Value

The color of IKM powder was measured in terms of reflec-tance value using a reflectometer (CL-28, Elico, Hyderabad,India; 450 nm filter). Five measurements were made foreach sample by placing the reflectometer’s exposure unit onas many different points on the covered Petri dish, and a

A. JHA and A.A. PATEL SHELF LIFE OF KHEER MIX POWDER


mean value of reflectance was recorded. Color was exposedin terms of absorbance (B): B (%) = 100 - reflectance (%).

Total and Free HMF Formation

The progression of Maillard reaction was determined interms of free (FHMF) and total (THMF) hydroxymethyl-furfural content using the method of Keeney and Bassette(1959). A standard curve was obtained in two parts, whichcould be described by the following regression equations:

Y X= − −( )88 57 236 for 1 2 mol L. .0 0 0 0 μ (1)

Y X= − −( )88 489 9162 for 2 1 mol L. .0 0 00 μ (2)

whereX = observed optical density at 443 nm andY = mmol of HMF/L.

Computation of Reaction Kinetics

The total and free HMF formation in kheer mix powder wasfound to follow first-order reaction kinetics. The first-orderreaction rate constants (k) were, therefore, calculated usingthe following expression:

lnC

Ck

0

= − (3)

whereC0 = initial concentration of the reactant andC = concentration of the reactant at time “t”.

The temperature dependence of “k” was describedaccording to the Arrhenius equation:

k A eE

RT=−

0

a(4)

whereA0 = Arrhenius constantR = universal gas constant, 8.314 J/mol °KT = absolute temperature, °KEa = activation energy, J/mol.

The thermodynamic equation parameters were obtainedby using the mathematical expressions based on absolutereaction rate theory.

kk T

he eB

S

R

H

RT= ⋅ ⋅−Δ Δ* *

(5)

wherekB = Boltzmann’s constant, 1.38 ¥ 10-23 J/°KH = Planck’s constant, 6.63 ¥ 10-34 J.SDS* = entropy of activation, J/mol °KDH* = enthalpy of activation, J/mol.

The enthalpy was calculated from Ea obtained from theexperimentally obtained reaction rate constants using thefollowing relationship:

ΔH E RTa* = − (6)

The free energy of activation (DG*, kJ/mol) was obtainedfrom the following relationship:

Δ Δ ΔG H T S* * *= − (7)

Development of Shelf-life Prediction Models

For prediction of shelf life, a set of mathematical equationswere developed combining kinetic functions and the func-tional relationship of variables relating to physicochemicalparameters and loss of sensory quality. The equations, thenselected, were integrated with the Arrhenius relationshipbetween rate constants and temperature of storage for thesevariables.

RESULTS AND DISCUSSION

Color

The absorbance value (100 - % reflectance) of IKMpowder increased during the storage. The net increase atdifferent temperatures is shown in Fig 1. The rate ofincrease in browning intensity was higher at higher tem-perature of storage. It was noted that for the product

0

5

10

15

20

25

30

0 2 4 6 8 10 12 14 16 18 20 22 24

Ct-

Co

(abs

orba

nce,

%)

Time (weeks)

45 °C

37 °C

30 °C

FIG. 1. CHANGE IN THE ABSORBANCEVALUE OF INSTANT KHEER MIX POWDERSTORED AT DIFFERENT TEMPERATURES



stored at 30C, the absorbance value increased from initial5.0 to 13.3 over a period of 24 weeks. At 37C, the absor-bance value increased to 25.0 after 16 weeks, at 45C, theabsorbance value recorded was 30.6 after only 8 weeks ofstorage. Maillard browning is expected to explain theincrease in absorbance values. Other workers in the pasthave also noted that significant nonenzymatic browningtakes place in dried milks as a function of storage tempera-ture and time. Kneifel et al. (1992) used tristimulus colormeasurement and reported that the b value correlatedwell with the degree of nonenzymatic browning in wheypowder, and its increase in both powder and reconstitutedmilk was attributed to Maillard reaction, which was pro-moted by high Aw and high temperature of storage. In astudy on medium-heat WMP stored at 50C Hunter bvalue, after an initial decrease, increased from the eighthday of storage to 43rd day (Nielsen et al. 1997a,b;Stapelfeldt et al. 1997). Discoloration progresses slowlyduring normal storage, but rapidly if either the moisturecontent of the powder or the storage temperature is high.The Arrhenius relationship provides a good description ofthe temperature dependence of the color change (Toribioand Lozano 1984).

Total HMF

As can be seen from Fig. 2, total HMF formed as a conse-quence of progression of Maillard reactions increased withthe increase in storage time and temperature. In fresh kheermix powder, the average value recorded was 5.0 mmol/L,which increased to 21.74 mmol/L after 24 weeks of storageat 30C. At 37 and 45C, the total HMF content increasedto 30.4 and 56.3 mmol/L after respective storage durationsof 16 and 8 weeks. Mrithyunjaya and Bhanumurthi(1987) observed an increase in HMF content from 2.47 to7.64 mmol/g in dried whole milk on storage at 37C for 6months. In SMP, the HMF content increased from 5.68 to28.43 mmol/g after storage for 240 days at room tempera-ture (Caric et al. 1984). Paul (1984) observed the HMF

content to increase from 119.62 to 251.24 mmol/g in lactosehydrolyzed infant formula stored at 30C for 12 months.

Free HMF

The free HMF measures only HMF formed in the productand does not include the potential HMF derived from otherbrowning intermediates (Keeney and Bassette 1959). Theincrease in the free HMF value is plotted against storageperiods for all the three temperatures of storage (Fig. 3).The initial concentration of free HMF was 1.27 mmol/L,which increased to 10.4 mmol/L after 24 weeks of storageof the kheer mix powder at 30C, whereas it increased to19.5 mmol/L after 16 weeks at 37C. The rate of free HMFformation was much faster at 45C as the level reached afteronly 8 weeks of storage was 34.9 mmol/L. As such, no reportis available about the effect of time and temperature ofstorage on free HMF formation in dried milk. However, afew reports on the formation of free HMF during UHT pro-cessing of milk and its increase during storage are available(Horak 1980; Singh 1991).

Reaction Kinetics

The change in color of kheer mix powder was found to be

a zero-order reaction. The Arrhenius plot (In k versusI

T)

revealed a straight line (Fig. 4). The Ea, Arrhenius cons-tant and Q10 value for the reaction were 106.50 kJ/mol,9.846 ¥ 1017 M/week and 3.8, respectively (Table 1).Enthalpy of activation (DH) for color change rangedfrom 103.98 to 103.85 kJ/mol, entropy of activation (DS)ranged from -246.55 to -229.11 J/mol °K and free energyof activation (DG) varied from 74.81 to 72.96 kJ/molfor the temperature range from 30 to 45C. The total HMFformation in kheer mix powder followed first-orderreaction kinetics as also observed in UHT milk (Singh1991). The Arrhenius plot (Fig. 5) showed a single straightline and the Ea obtained was 77.0 kJ/mL (Table 1). The

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14 16 18 20 22 24

Ct /

Co

(to

tal H

MF

, m

mo

le/l)

Storage period (weeks)

45 °C

37 °C

30 °C

FIG. 2. CHANGE IN THE TOTALHYDROXYMETHYLFURFURAL (HMF) OFINSTANT KHEER MIX POWDER STOREDAT DIFFERENT TEMPERATURES



Arrhenius constant and Q10 values were 1.517 ¥ 1012 M/week and 2.7, respectively. Enthalpy of activation (DH) forchange in total HMF ranged from 74.55 to 74.42 kJ/mol,entropy of activation (DS) ranged from -247.29 to-234.63 J/mol °K and free energy of activation (DG) variedfrom 75.04 to 74.68 kJ/mol for the temperature range from30 to 45C. The formation kinetics of free HMF could bedescribed by a first-order reaction. Ea obtained from theArrhenius plot (Fig. 6) was 75.0 kJ/mol, while the Arrhe-nius constant and Q10 values were 8.261 ¥ 1011 M/week and2.59, respectively (Table 1). Enthalpy of activation (DH) for

change in free HMF ranged from 72.56 to 72.43 kJ/mol,entropy of activation (DS) ranged from -245.84 to-233.42 J/mol °K and free energy of activation (DG) variedfrom 74.56 to 74.30 kJ/mol for the temperature range from30 to 45C (Table 1).

The activation entropies for all the reactions studied werefound to be negative, indicating that activated complexin these reactions are well ordered structures. Increase instorage temperature resulted in a decrease in DS for allreactions, suggesting increased randomness of activatedcomplex and increased salvation of the reactants.

0

5

10

15

20

25

30

35

0 2 4 6 8 10 12 14 16 18 20 22 24

Ct/ C

o(f

ree H

MF

, m

mol/l)

Storage period (weeks)

45 °C

37 °C

30 °C

FIG. 3. CHANGE IN THE FREEHYDROXYMETHYLFURFURAL (HMF) OFINSTANT KHEER MIX POWDER STOREDAT DIFFERENT TEMPERATURES

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

0.00312 0.00316 0.0032 0.00324 0.00328 0.00332

ln k

1/T, K-1

FIG. 4. ARRHENIUS PLOT FOR CHANGE INTHE COLOR (ABSORBANCE) OF INSTANTKHEER MIX POWDER DURING STORAGE

TABLE 1. KINETIC PARAMETERS OF BROWNING-RELATED CHANGES IN STORED KHEER MIX POWDER

Variables

Parameters

Temperature(C)

Rate constant(k), per week

Apparent activationenergy (Ea) (kJ/mol)

Frequency factor (Arrheniusconstant, A0) (M/week) Q10

DH(kJ/mol)

DS(J/mol °K)

DG(kJ/mol)

Color 30 3.798 ¥ 10-1 106.50 9.846 ¥ 1017 3.860 103.98 -246.55 74.8137 1.1949 ¥ 10o 103.92 -237.48 73.7245 3.355 ¥ 10o 103.85 -229.11 72.96

Total HMF 30 2.266 ¥ 10-1 77.07 1.517 ¥ 1012 2.658 74.55 -247.29 75.0437 8.685 ¥ 10-1 74.49 -242.47 75.2445 3.212 ¥ 10o 74.42 -234.63 74.68

Free HMF 30 3.110 ¥ 10-1 75.08 8.261 ¥ 1011 2.591 72.56 -245.84 74.5637 8.685 ¥ 10-1 72.50 -241.03 74.7945 3.212 ¥ 10o 72.43 -233.42 74.30

HMF, hydroxymethylfurfural.



Sensory Changes in Reconstituted Kheer

Changes in sensory scores of reconstituted kheer duringstorage of kheer mix powder are presented in Table 2.Reconstituted IKM was subjected to sensory profile analy-sis (on a 100-point intensity rating scale) and hedonicrating (on a 9-point scale). The average intensity rating forbrowning in reconstituted kheer increased gradually duringstorage, the increase being more pronounced at elevatedtemperatures: from initial 0.3 to 6.3 after 24 weeks at30C, 8.9 after 16 weeks at 37C and 15.8 after 8 weeks at45C. Maillard browning was also reflected in increasingHMF values for the kheer mix powder during storageas discussed earlier. The color score of the productcorrespondingly decreased from initial 8.75 (“likeextremely”) to 7.6, 7.5 and 7.9 (“like extremely”), afterstorage at 30, 37 and 45C, respectively. Analysis of vari-ance (ANOVA) for intensity rating of browning revealedthat the effect of the period of storage was significant

(P < 0.05) at all temperatures of storage, the rating beingsignificantly higher after 8, 2 and 1 week at the respectivetemperatures. Similarly, statistical analysis of the hedonicrating data exhibited significantly decreased scores afterthese storage periods (P < 0.05).

The combined effect of the decreasing color and flavorscores of the reconstituted kheer from stored kheer mixpowder as discussed in the preceding sections was that theoverall acceptability (hedonic rating) score declined from8.38 (“like extremely”) for the reconstituted fresh productto 7.75 (close to “like extremely”) for kheer mix powderstored at 30C for 24 weeks, 7.41 (“like very much”) for kheermix powder stored at 37C for 16 weeks and 7.19 (“like verymuch”) for kheer mix powder stored at 45C for 8 weeks. TheANOVA, however, showed that the decline in overall accept-ability rating was significant only at 45C, the difference inthe product rating becoming larger than the critical differ-ence after 2 weeks storage at this temperature. The productkept well for at least 16 weeks at 37C and 24 weeks at 30C.

-3.00

-2.50

-2.00

-1.50

-1.00

-0.50

0.00

0.00312 0.00316 0.0032 0.00324 0.00328 0.00332

ln k

1/T, K-1

FIG. 5. ARRHENIUS PLOT FOR CHANGE INTHE TOTAL HYDROXYMETHYLFURFURAL(HMF) OF INSTANT KHEER MIX POWDERDURING STORAGE

-3.00

-2.50

-2.00

-1.50

-1.00

-0.50

0.00

0.00312 0.00316 0.0032 0.00324 0.00328 0.00332

ln k

1/T, K-1

FIG. 6. ARRHENIUS PLOT FOR CHANGEIN THE FREE HYDROXYMETHYLFURFURAL(HMF) OF INSTANT KHEER MIX POWDERDURING STORAGE



Interrelationships between VariousPhysicochemical and Sensory Changes

Parameters of linear regression and log-log regression forbrowning and related changes in IKM powder during storageare shown in Table 3. Parameters with high coefficient ofdetermination were selected for prediction modelling.

The interrelationships between physicochemical and sensorychanges during storage are presented in Table 4, citingrelevant equation numbers from 8 to 13. The browningintensity of the reconstituted kheer was found to be positivelycorrelated (r = 0.94, P < 0.01) with absorbance, the corre-sponding regression exhibiting 88% changes in browningintensity as explained by absorbance. Similarly, browningintensity of the reconstituted kheer was positively correlatedwith change in total HMF (r = 0.95, P < 0.01). It was observedthat 91% of the variation in sensorily perceived browningcould be explained by the total HMF concentration(R2 = 0.91). Overall acceptability of the reconstituted kheerwas negatively correlated with change in total HMF(r = -0.94, P < 0.01) and also with change in free HMF(r = -0.93, P < 0.01). Corresponding regression exhibited that84% variation in the overall acceptability could be explainedeither by total HMF or by free HMF.

Shelf-life Prediction Models

The kinetic approach to predict the shelf life of any foodproduct requires generation of information relating to thephysicochemical parameters and loss of sensory quality as afunction of storage time and temperature. A set of math-ematical equations are then developed combining kineticfunctions and the functional relationship of variables. Thedevelopment of mathematical models for predicting shelflife of stored IKM was therefore in two steps. In the first

TABLE 2. CHANGES IN SENSORY SCORES OF RECONSTITUTED KHEERDURING STORAGE OF INSTANT KHEER MIX POWDER

Temperatureof storage (C)

Storageperiod(weeks)

Color(max. 9)

Flavor(max. 9)

Overallacceptability(max. 9)

30 0 8.75 8.35 8.504 8.62 8.31 8.438 8.46 8.27 8.41

12 8.25 8.24 8.0016 7.93 8.19 7.9220 7.80 8.14 7.8424 7.60 8.00 7.75

37 0 8.75 8.35 8.504 8.51 8.27 8.408 8.28 8.12 8.00

12 7.67 7.88 7.7616 7.50 7.56 7.41

45 0 8.75 8.35 8.502 8.43 8.14 8.314 8.11 7.90 7.706 7.77 7.72 7.358 7.30 7.50 7.19

TABLE 3. PARAMETERS OF LINEARREGRESSION (y = mx + c) AND LOG-LOGREGRESSION (y = em.lnx+lnc) FOR BROWNINGAND RELATED CHANGES IN KHEER MIXPOWDER DURING STORAGE

Independentvariable (x)

Dependentvariable (y) M lnc

Coefficient ofcorrelation

Coefficient ofdetermination (R2)

Absorbance Overallacceptability

-0.037 8.47 -0.86** 0.74

TBA -0.038 1.96 -0.84** 0.71Total HMF -0.049 2.19 -0.92** 0.84Free HMF -0.042 2.14 -0.92** 0.84Browning intensity -0.034 2.11 -0.84** 0.71Flavor score 0.873 0.27 -0.77** 0.59

* P < 0.05.** P < 0.01.HMF, hydroxymethylfurfural.

TABLE 4. INTERRELATIONSHIPS BETWEENPHYSICOCHEMICAL AND SENSORYPARAMETERS

Regression equationCorrelationcoefficient

Equationnumber

Browning intensity = 0.476 ¥ absorbance - 1.14 0.94* 8Browning intensity = 0.278 ¥ total HMF + 1.10 0.95* 9Browning intensity = 0.436 ¥ free HMF + 1.57 0.94* 10Flavor score = -3.578 ¥ TBA + 8.17 -0.74* 11Overall acceptability = e-0.049¥ln(total HMF)+2.19 -0.94* 12Overall acceptability = e-0.042¥ln(free HMF)+2.14 -0.93* 13

* P < 0.01.HMF, hydroxymethylfurfural.



step, from among several regression equations described inthe preceding section, those with high coefficients of deter-mination (R2 = 0.78 or more) were selected. It was observedthat the overall acceptability of the product during storagecould be best described by three quality indices viz. totalHMF, free HMF and change in color measured in terms ofabsorbance. The equations then selected were integratedwith the Arrhenius relationship between rate constants andtemperature of storage for these variables. The predictiveequations thus developed are being described hereunder:

Shelf-life Model Based on Overall Acceptability ofKheer and Changes in Absorbance of Kheer MixPowder. Changes in color (absorbance = 100 - % reflec-tance) as a result of browning in IKM powder duringstorage was also found to have a good correlation with theoverall acceptability (OA) of the reconstituted kheer. Thechange in absorbance during storage could be related toperiod of storage using a zero-order reaction kinetics andthe resulting shelf-life model is given below:

OA Abs t e= − ( ) + × ⋅⎛

⎝

− ×+( )8 47 0 037 9 846 100

17

106 50 10

8 314 273

3

. . ..

. θ⎜⎜⎞

⎠⎟

⎡

⎣⎢⎢

⎤

⎦⎥⎥

(14)where Abs0 = absorbance (%) at time t = 0.

Comparison of the predicted values and actual values ofOA revealed a high reliability of the model as indicated bylow values of RMS (0.65, 0.30 and 0.26 for 30, 37 and 45C,respectively). Change in color of UHT milk measured as% reflectance was used for prediction of shelf-life model(Singh 1991). A shelf-life prediction model for acceptability ofsweetened condensed milk could also be developed based onchanges in its color measured as absorbance (Patel et al. 1996).

Shelf-life Model Based on Overall Acceptability ofKheer and Changes in Total HMF Content of KheerMix Powder. In view of the high correlation coefficientobserved between the OA of reconstituted kheer and totalHMF content of IKM powder during storage, the followingequation was developed combining the regression of OA ontotal HMF:

ln

. . ln ..

.

OA

THMF t e

( ) =

− ( ) + × ⋅− ×

+2 19 0 049 1 517 10012

77 07 10

8 314 2

3

θ 773( )⎛

⎝⎜

⎞

⎠⎟

⎡

⎣⎢⎢

⎤

⎦⎥⎥(15)

whereOA = overall acceptabilityTHMF0 = total HMF content in mmol/L at time t = 0t = time (weeks)q = temperature of storage.

The fitness of this model was also tested by calculatingroot mean square percent (RMS, %), as described by Patiland Patel (1992):

RMSP P

Pi

n

%( ) =−⎛

⎝⎜⎞⎠⎟ ×

=∑1

1002

1nobs pred

obs

(16)

wherePobs = observed parametric valuePpred = predicted parametric valuen = number of observations.

Applicability of the model developed for predictingoverall acceptability on the basis of changes in the totalHMF was found to be good, as the RMS percentage waslow viz. 0.99, 0.23 and 0.24 at 30, 37 and 45C, respectively.Changes in HMF content during storage has also been usedfor developing a shelf-life prediction model for the overallacceptability of UHT milk (Singh 1991).

Shelf-life Model Based on Overall Acceptabilityof Kheer and Free HMF Content of Kheer MixPowder. As for total HMF, the high correlation betweenoverall acceptability of kheer and free HMF content of kheermix was also combined with the kinetic parameters:

ln

. . ln ..

.

OA

FHMF t e

( ) =

− ( ) + × ⋅− ×

+2 14 0 042 8 261 10011

75 08 10

8 314 2

3

θ 773( )⎛

⎝⎜

⎞

⎠⎟

⎡

⎣⎢⎢

⎤

⎦⎥⎥(17)

where FHMF0 = free HMF content mmol/L at time t = 0.The fitness of this model was tested and the very low

RMS percent obtained (0.37, 0.13 and 0.38 at 30, 37 and45C, respectively) meant that the model could effectivelypredict the overall acceptability of the product.

Potential Shelf Life of the KheerMix Powder

Of the above three models discussed, the one based on freeHMF showing the smallest deviation of the predicted valuesfrom the actual values in the range of storage periodincluded in the study was employed to determine the poten-tial shelf life of the product at 37C. For this the followingassumptions were made:(1) As per the acceptability scale used for sensory eva-luation of the product, an overall acceptability score of 4(corresponding to “like moderately”) for the reconstitutedproduct would be the minimum acceptable or shelf life-determining score;(2) The shelf-life model based on data for storage studies of16 weeks at 37C would be valid even beyond this period.

It was found that the potential shelf life of the kheer mixpowder was 92 weeks at 37C. This was fairly comparable



with the shelf life of most powdered products includ-ing milk powders. Such a shelf life would facilitate thewide-scale marketing of the product under the tropicalconditions prevailing in India and also promote value addi-tion, exports, and product diversification for the food anddairy industry.

CONCLUSIONS

A conventional product like kheer, having a poor shelf life inliquid form, could be developed as a spray-dried mix withcommercially useful shelf life of about 92 weeks at 37C. Drymix could be easily reconstituted into kheer and the producthad a high sensory rating. Kheer mix powder, during storageat 30, 37 and 45C underwent changes in color, total andfree HMF content, which could be correlated with sensorychanges in the product upon reconstitution. The changein color of kheer mix powder followed zero-order reactionkinetics. The formation kinetics of total and free HMFcould be described by a first-order reaction. There was ahigh correlation between total HMF content of kheermix powder and sensory acceptance of the reconstitutedproduct; therefore, a shelf-life prediction model could bedeveloped by combining the rate constants and temperatureof storage. It can be concluded that a conventional-likeproduct like kheer, could be brought to the forefronts ofindustrial application from the confines of domestickitchen. This work can also find relevance for several othertraditional dairy and nondairy foods.

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kinetics of hmf formation during storage of instant kheer mix powder and development of a shelf-life...

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