kinetics of nonenzymatic browning in cheddar ...9.58 0.84 as the water activity increased, mold...

KINETICS OF NONENZYMATIC BROWNING IN CHEDDAR CHEESE POWDER DURING STORAGE

MERAL KILIC', K. MUTHUKUMARAPPAv and SUNDARAM GUNASEKARAPa3

'Food Science Department 2Biological Systems Engineering University of Wisconsin-Madison

460 Henry Mall Madison, W 53706

Accepted for Publication March 24, 1997

ABSTRACT

Nonenzyman'c browning (NEB) in Cheddar cheese powder during storage was investigated in the water activity (a,,,) and temperature ranges of 0.48-0.85 and 20- 4OC, respectively. R e NEB obeyed zero-order reaction kinetics during storage. Activation energies and Q,o values were in the range of 15.1-22.3 kcal/mole and 2.2-3.5, respectively. The NEB increased with increasing temperature and storage time. There was an a, maxim at 0.43 for NEB at 20C. At 30 and 4OC, NEB decreased with increasing a, A generalized NEB model for Cheddar cheese powder during storage was developed based on Arrhenius equation to describe NEB as a function of a, and temperature. Powders stored at 20 and 30C were evaluated for quality aspects. Maximum storage stability was obtained in powders stored at 4, of 0.54 at 20C for five months based on an overall desirability score of 3.5 on a %point scale. lh? average score offresh powders were 4.7 throughout the storage study 7.

INTRODUCTION

Cheddar cheese powder is widely used as a food ingredient. Powdered cheese is fairly inexpensive to ship and can be stored longer than the corresponding regular cheese. However, the quality of cheese powder depends on how it is stored. Degradation of flavor, color, and texture occur under such adverse storage conditions as those found in hot and humid climates. Nonenzymatic browning (NEB) is one of the major detrimental reactions that occur during storage of cheese powders (Kosikowski 1977). The NEB results in the formation of brown discoloration, off-flavor, and degradation of nutritional value.

'Author for correspondence. Tel: (608)262-1019, Fax: (608)262-1228, e-mail: [email protected] wisc.edu

Journal of Food Processing and Preservation 21 (1997) 379-393. All Rights Reserved. %pyright 1997 by Food Br Nutrition Press, inc., Trumbull, Connecticut. 379

380 M. KILIC, K. MUTHUKUMARAPPAN and S. GUNASEKARAN

The NEB is a ubiquitous reaction in food products containing reducing sugars and proteins. Dairy foods containing lactose are readily susceptible to NEB. Primary NEB products could react with other food components, such as lipids, and other carbonyl compounds and enhance browning (Rizzi 1994). The occurrence and progress of NEB are determined by the composition of the food product and temperature and water activity (a,,,) of storage environment. The Arrhenius equation is commonly used to describe the temperature dependence and to model the NEB reaction (Mizrahi ef al. 1970; Thomas ef al. 1977; Saguy ef al. 1978; Labuza and Saltmarch 1981a; Singh et al. 1983; De Kanterewicz and Chirife 1986; Rhi i ef al. 1988; Franzen et al. 1990; Cohen et al. 1994; Rapusas and Driscoll 1995). Zero-order reaction kinetics has been used to describe the NEB reaction, although first-order reaction kinetics has also been employed. Brown pigment formation generally follows zero-order reaction kinetics, whereas lysine loss follows first-order reaction kinetics (Brien and Morrissey 1989). The NEB was studied extensively in dried dairy products (Saltmarch ef al. 1981; Labuza and Saltmarch 1981a; De Kanterewicz and Chirife 1986; Buera et al. 1990; Franzen ef al. 1990) but not much information is available for NEB in cheese powders. The information about the NEB in cheese powders during storage would allow manufacturers to increase the quality and shelf-life of cheese powders. Cheese powders contain higher amounts of fat and protein with much less amounts of lactose compared to milk and whey powders. Addition of these powders to cheese powder in the formulation provides lactose that could be used for browning. Thomas (1969) also reported that addition of young cheese, 1-3 months, and skim milk enhanced browning in processed Cheddar cheese. On the other hand, addition of aged cheese to cheese powder may also increase the potential for browning by providing amino and carbonyl groups for the reaction (Lindsay 1996).

Our objectives were to determine the kinetics of NEB in Cheddar cheese powder during storage as a function of temperature and water activity and to evaluate the storage stability of powders organoleptically in regards to NEB under the conditions studied.

MATERIALS AND METHODS

Materials

Two replicate lots (20 kg each) of spray-dried process Cheddar cheese powder were obtained from Mid-America Farms, Inc. (Springfield, MO). The compositions of powders are given in Table 1. The powders were kept at -28C in a freezer until they were used for the experiments.

NONENZYMATIC BROWNING IN CHEESE POWDER 381

Galactose 0.4 0.2 (%)d

>

Equilibration and Storage of Powders

Different saturated salt solutions, Mg(N03)2, NaNO,, NaCI, and KCl (Fisher Scientific, Inc., Chicago, IL) were used to provide constant a, conditions for the storage of powders (Labuza 1984). Saturated salt solutions were prepared in plastic jars with distilled water to obtain a, in the range of 0.48-0.85 at temperatures of 20, 30, and 40C. The solutions were kept in a temperature- controlled incubator overnight to ensure saturation. The water activities of the solution were verified with CX-1 water activity system (Decagon Devices, Inc., Pullman, WA) at corresponding temperatures. The exact water activity values were taken from Labuza (1984) except for a, of NaNO, which was measured by means of the water activity system (Table 2). The jars were shaken after each opening to ensure saturation throughout the storage study.

Both lots of cheese powders were spread out on cheesecloths and equilibrated to corresponding a, values of available salt solutions in temperature- and humidity-controlled rooms (Classic Modular Systems, Inc., Two Rivers, WI) for

Salt (%y Ash (%)f

TABLE 1. COMPOSITION OF CHEDDAR CHEESE POWDERS

4.7 5.4

10.6 11.1

1 Component 1 ~ o t ~ l 1 L;,: 1 Moisture (%)’

Protein (%)b 29.2 27.9

I Fat(%Y I 48.3 I 51.1 I Lactose (“h)‘ 1 5.4 3.4

a Vacuum oven method (Marth, 1978)

” Rose-Gottlieb method (Marth, 1978)

Chloride Analyzer method (Johnson and Olson, 1985b)

* Quinhydrone method (Van Slyke and Price. 1979) ‘measured by CX-1 water activity system

Kjeldahl method (Marth, 1978)

Enzymatic Procedures (Johnson and Olson, 198Sa)

@iarth, 1978)


NaNO,'

NaCl

KC1

7-10 days. Equilibration was continued until the mass of reference samples (10- 20 g) did not change by more than 0.01 g. After equilibration, powders were transferred into stainless steel baskets containing Whatman No.4 filter paper. Baskets of powders were hung from the lids of the jars containing saturated salt solutions at corresponding G. The jars were tightly closed and stored in temperature-controlled rooms at 20, 30 and 4OC for six months. Samples were taken weekly for the first month and then monthly during storage and kept in a freezer until they were used for chemical and sensory analyses.

40 0.48

20 0.63 30 0.62 40 0.61

20 0.76 30 0.75 40 0.75

20 0.85 30 0.84 40 0.82

TABLE 2. WATER ACTIVITIES (aJ OF SATURATED SALT SOLUTIONS USED IN THE STUDY

(From Labuza, 1984)

salt I Ternperature("C) I aw I I

Browning Index Measurements

The Browning index of the powders was measured by using an enzymatic digestion method (Palombo et al. 1984) which releases the brown pigments. Samples were freeze-dried (The Virtis Company, Model No. 10-100, Gardiner, N.Y.) for 22 h before analysis. One gram of freeze-dried powder was reconstituted with 5 mL of distilled water at 45C, and 1.5 mL of the mixture was transferred into test tubes containing 0.4 mL of pronase solution (contained 10 mg pronase, Calbiochem 53702; 70,000 PUWg) per mL Tris buffer (0.2M hydroxy(methyl)aminomethane, 0.2 M HCI, and distilled water (1: 1:2), pH 7.00 with 50 mh4 CaC12.H20) (Franzen et uZ. 1990). The tubes were incubated at 45C for 120 min and then cooled with ice/water. After addition of 0.15 mL of 100%(w/v) TCA (trichloroacetic acid), the mixture was centrifuged at 4,700 rpm for 20 min and the contents filtered through Whatman No. 1 filter paper. The


absorbancies of the clear solutions were measured at 420 nm (A420) and 550 nm (A,,o) using a Beckman DU-64 spectrophotometer (Beckman Instruments, Inc., Schaumburg, IL). The browning index was expressed in terms of optical density (OD = A420-As50) per gram of solid material. The measurements were done in duplicates.

NEB Model Development

Browning data for each %-temperature condition during storage were analyzed for zero-, frst-, and second-order reaction kinetics and the exponential model of Toribio and Lozano (1984). A generalized NEB model was developed using linear and nonlinear regression analyses. All statistical analyses were performed with Statgraphics@ Plus software (STSC 1992).

Evaluation of Storage Stability

Powders stored at 20 and 30C were assessed for quality on a seven-point scale (Stone and Side1 1985) by three experienced dairy judges. Five-gram samples packed in pouches were evaluated by the judges for browning, texture, off-flavor, cheese-flavor, and overall desirability. Samples of the original powders kept in the freezer were also scored each time as controls. The analyses were continued for two months for powders stored at 30C and for six months for powders stored at 20C.

RESULTS AND DISCUSSION

Significant browning occurred in cheese powders stored at 30 and 40C with relatively less browning at 20C as indicated by the browning parameters in Table 3. From the compositional analysis (Table l), skim milk powder might have been added to the cheese slurry in the manufacturing process providing lactose necessary for the initiation and progress of the NEB. Besides lactose, proteins and lipids may have provided carbonyl and amino compounds necessary for the progress of NEB reaction (Lindsay 1996). Initial products of NEB may also be present in powders as a result of heat treatment during manufacture that may lead to progress of the NEB during storage.

Brown color development was about the same at all a, conditions at 20C except at a, of 0.63 during the first month of storage. Browning was higher during this time and the rest of the storage at a, of 0.63 at 2OC. Thus, a, of 0.63 could be considered as an a, maxima for browning at 20C. This falls within the water activity maxima range of 0.60-0.80 for NEB in foods (Labuza and Saltmarch 1981b). NEB decreased with increasing a, at 30 and 40C (Fig. 1) without exhibiting an a, maxima.


k x ld(OD/g Standard solid-day) Error for k x lo’

1.94 0.04 2.08 0.06 1.47 0.06 1.82 0.01

12.01 0.05 10.04 0.04 5.89 0.26 4.29 0.37

22.17 1.82 15.82 2.46 9.98 0.82 9.58 0.84

As the water activity increased, mold growth became favorable in the cheese powders. Visible mold growth occurred at a, of 0.85 after one month of storage at 20C, and at a, of 0.84 after five months of storage at 30C. However, there was no visible mold growth at 40C, at a, throughout the storage period. As a result, there were limited data for interpretation of NEB at 20 and 30C.

There was no initial lag period for NEB under any of the conditions studied although the presence of an initial lag period for NEB in foods has been previously reported by some researchers (Saguy er al. 1978; Franzen er al. 1990). Cheddar cheese powder may contain initial NEB products formed during manufacturing. This may lead to continuation of NEB without any lag during storage. Instead, we observed flattening in the NEB values with prolonged storage at 30 and 40C.

R2

0.99 0.99 0.97 0.95

0.95 0.97 0.96 0.90

0.90 0.72 0.90 0.90

TABLE 3. ZERO-ORDER REACTION PARAMETERS (B, AND k) OF NEB AT DIFFERENT

TEMPERATURE -a, CONDITIONS

Temperature CC) 20

30

40

a,

0.54 0.63 0.76 0.85

0.51 0.62 0.75 0.84

0.48 0.61 0.75 0.82

0.09 0.13 0.10 0.10

0.04 0.14 0.13 0.20

0.53 0.75 0.34 0.27

NEB increased with increasing temperature from 20 to 40C and storage time. At 20C, brown discoloration increased with time at an approximately constant rate at each a, condition. However at 30C, browning slowed at % of 0.75 and more drastically at a, of 0.84 after two months of storage. The same trend was observed at 40C under all a, conditions after about one month of storage. This could be due to the initial rapid reaction rate in higher temperatures that causes rapid depletion of reactant species and a slower reaction rate. As seen in Fig. 1 at 40C, the optical density (OD) value after about one month of storage was around 1.7 at a, of 0.48 and 0.61. This value was much higher than the


corresponding OD values at 20 and 30C. The dilution effect of reactant species may be another reason for the decrease in the reaction rate at higher %. Reactions other than NEB, such as mold growth and lipid oxidation may also decrease the NEB rate at 30 and 40C.

a, cab Rediem

0.48 0 - 4 - 0.61 A - -

. 0 . 7 5 0 ..............

X

I I I

0 50 100 150 ZOO

storage lime (day)

FIG. 1 . BROWNING IN CHEDDAR CHEESE POWDER AT VARIOUS a, AT 4OC (lines: zero-order reaction)

NEB Model

The effects of h,, storage temperature, and time on NEB were found to be statistically significant (P<O.O5) Browning data were first fitted to an exponential model (Toribio and Lozano 1984) since there was a decrease in NEB at 30 and 40C with prolonged storage,

B = a - b exp(-kt) (1)

Explanations for all symbols and notations are provided separately under nomenclature. The fit of this model was not good at 20 and 30C compared to


40C. First- and second-order reaction kinetics were also unsuitable for the experimental data. the fit of the zero- order kinetic equation was relatively better under all storage conditions (Table 3). The Rz values were at least 0.90 or better for all storage conditions except at a,,, of 0.61 at 40C. Thus, zero-order reaction kinetics was chosen to describe NEB at different conditions during storage,

B = B, + kt (2)

Brown pigment formation in foods has generally been found to follow zero- order reaction kinetics (Warmbier d al. 1976; Rhim el al. 1988; De Kanterewicz and Chirife 1986; Buera et al. 1990; Franzen ef al. 1990) even though there have been rare reports of different reaction mechanisms for specific foods (Saguy el al. 1978; Toribio and Lozano 1984). The zero-order reaction rate constant (k) increased with increasing storage temperature at all the a, studied. The zero- order reaction rate constants for processed cheddar cheese powder were found to be greater than the values reported by Labuza and Saltmarch (1981a) for whey powder at slightly higher temperature and a,,, conditions. Whey powder contains higher amounts of lactose and less amounts of lipids and proteins compared to cheese powder. The results from this study indicate that lipids and proteins may provide compounds that contribute to browning.

The Arrhenius equation was used to determine the temperature dependence of NEB and to calculate activation energies (EJ,

k = k, exp -2 [ :TI (3)

Qlo values were calculated according to Eq. 4 (Labuza and Saltmarch 1981b):

2.189 Ed

T (T+10) log Q, , = (4)

Activation energies and Qlo values (Table 4) were within the ranges reported for different food products, 16-30 kcal/mole and 2-6, respectively (Labuza and


c E, (kcaYmole)* Qio(20-30 C)

0.51 22.3 f 5.9 3.5

0.62 . 18.6f5.5 2.9

0.75 17.5 f 4.2 2.7

0.84 15.1 f 0.01 2.4

Baisier 1992). The higher Qlo value at a, of 0.51 supports the higher reaction rates at low a,.

Qm (3040 C) 3.3

2.7

2.5

2.2

TABLE 4. ACTIVATION ENERGIES (EJ AND Qlo VALUES FOR VARIOUS a,

The Arrhenius equation was used as a basis for developing a generalized NEB rate constant as a function of temperature and a, during storage. The EJR term was treated as a constant in the model, since the activation energies were close to each other. The Arrhenius frequency factor k, was found to be linearly related to a, and was incorporated into the model as a parameter. The average temperature (303.15 K) in the study was used as a reference temperature to improve the fit of the model (Mishkin er al. 1983; Singh et al. 1983; Rapusas and Driscoll 1985). Details of the model are presented in Kilic (1995). The final generalized NEB model was

Model fit was satisfactory with an R2 of 0.91 and low standard errors for the model parameters (Table 5). The model was excellent in predicting the rate constants at 30 and 40C but it predicted high k values for 20C (Fig. 2). This deviation from the model could be due to relatively lower reaction rates at 20C compared to those of 30 and 40C. The NEB rate increases with increasing temperature and decreasing a, according to the model developed.

Storage Stability

The results of sensory assessment of color degradation were not in agreement with those browning index measurements. Color scores decreased with increasing a, that may be due to close browning rates and as a result, less perception of the

388

Parameters

A B C

M. KILIC, K. MUTHUKUMARAPPAN and S. GUNASEKARAN

Estimates Standard errors RZ RSS*

-3.38 0.23 0.91 9.E-05 -2.34 0.35

6829.05 768.84

TABLE 5. THE GENERALIZED NEB MODEL PARAMETERS AND ESTIMATES

TWKIWatlJre

2OC

3OC

0.01 -

4OC

A

0

A

0

0.001 I I I I

0.4 0.5 0.6 0.7 0.0 0.9

.r*

FIG. 2. BROWNING RATE CONSTANT (k) IN CHEDDAR CHEESE POWDER AT DIFFERENT a, AND TEMPERATURES

(lines: predicted from the generalized NEB model)

difference in color by the judges during the first month of storage. At 30C, color scores reached the same value, 3-3.5 after two months of storage (Fig. 3). On the other hand, increasing a,., effect was continuous at 20C during six months of storage. Again the reason may have been the low NEB rates resulting in the conflicting results from the sensory and chemical analyses. Textural degradation and off-flavor formation increased with increasing a, at 20 and 30C compared to


7 ,

0.62 A -- 0.75 ............

0.84 x

Y

0 10 20 30 40 50 60 70 Swage Time (day)

FIG. 3. COLOR DEGRADATION IN CHEDDAR CHEESE POWDER AT VARIOUS a, AT 30C

(Scores on a seven-point scale; lines: trend; arrow: control)

control and with prolonged storage (results not shown). Specific off-flavor notes perceived were burnt, cardboard, oxidized, stale, burnt feather, burnt rubber, brothy, scorched, acid, bouillon, hydrolyzed protein, musty, and gluey that are about the same for all a,- temperature conditions. These off-flavor notes were similar to those obtained with various dried milk products (Bassette and Keeney 1960; Ramshaw and Dunstone 1969; Walker 1972; Walker and Manning 1976). Cheese-like flavor intensity also decreased with prolonged storage at both temperatures.

Powders stored at a, of 0.54 at 20C and 0.51 at 30C were the most desirable throughout the storage (Fig. 4). Overall desirability decreased with increasing a,,, at 20C. This may be due to the degradation of flavor, and mold growth. At 30C, powders at a, of 0.62 were the most desirable. However, the overall desirability scores of powders at all a, decreased more rapidly than those of powders at 20C. If an overall desirability score of as high as 3.5 (average overall desirability score of fresh powders = 4.7) is taken as an acceptability limit, powders with a,,, of 0.54 at 20C would be acceptable for only five months. However, at 30C, powder with an a, of as low as 0.51 would be acceptable only five weeks. This may indicate the importance of NEB in determining the storage


7 &r

0.51

0.62 A

0.75 o

0.64 x

- -- .......... "

0 1 I I

FIG. 4. OVERALL QUALITY LOSS IN CHEDDAR CHEESE POWDER AT VARIOUS a, AT 30C

(Scores on a seven-point scale; lines: trend; arrow: control)

stability of powders considering only temperature effect on NEB. Powders at higher a,,, would be rejected immediately, or at most after one week of storage based on the same criterion as above. Even though browning is not significant, off-flavor formation renders dry milk products unacceptable at higher a, (Patton 1955). Thus the storage stability of cheese powders was much lower at high a,,, than at lower a,,,. Bullock et ul. (1963) found that regular Cheddar cheese powder air-packed in cans at 38C was not acceptable after three months, whereas powders stored at 10 and 24C were acceptable after six months. Earlier studies in cheese powders proved that packaging in nitrogen environments extends the shelf-life (Bradley and Stine 1963; Bullock et ul. 1963), but this method is not practiced due to high cost. Instead, powders are usually packed in air atmosphere and stored at room temperature. Lower water activities than the ones used in this study should be investigated to obtain the optimum a, for maximum storage stability at the common storage conditions.


N O M E N C L A m

model parameters model parameters water activity concentration of brown pigments (OD/g solid) concentration of brown pigments at time zero (OD/g solid) activation energy (kcal/mole) reaction rate constant (OD/g solid-day) Arrhenius frequency factor (OD/g solid-day) parameter describing temperature dependence of reaction universal gas constant (kcal/mole K) storage time (day) temperature (K unless otherwise noted)

ACKNOWLEDGMENT

We would like to thank Prof. R.C. Lindsay, Department of Food Science, University of Wisconsin-Madison, WI for his guidance in quality assessment of powders and helpful suggestions and comments during all phases of this study.

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21, 1-9.

kinetics of nonenzymatic browning in cheddar ...9.58 0.84 as the water activity increased, mold...

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