RHEOLOGICAL AND CHEMICAL PROPERTIES OF MOZZARELLA CHEESE

J. JOSEPH YUN', YIN LIANG HSEH', DAVID M. BARBANO], and CHARLES L. ROHN2

'Northeast Dairy Foods Research Center Department of Food Science

Cornell Univerxio, Ithaca, IVY 14853

'Rheometrics, Inc. One Possumtown Road Piscaraway, NJ 08854

(Manuscript received October 10, 1993; in final form April 18, 1994)

ABSTRACT

Dynamic viscoelastic parameters and chemical properties of Mouarella cheese produced using a "no-brine" cheese making method with 3 different cooking temperatures (38, 41, and 44C) were determined. Samples were stored for 3 weeh at 4C before dynamic mechanical analysis at 22C. G', G" and tan 6 were 5.8 - 6.4 x ld dyne/cm2, 1.9 - 2.1 x ld dyne/cm2, and 0.33 - 0.35, respectively, at 1 % strain and 10 rad/s. The percentage of intact a;-casein and /3-casein were 38-40% and 33-35% of total protein in the cheese, respectively. The range of cooking temperatures used in this experiment had little effect on dynamic viscoelastic properties or the amount of intact protein for the cheese.

INTRODUCTION

Rheological properties of Mozzarella cheese have been evaluated by compres- sion and stress relaxation tests (Cervantes et al. 1983; Casiraghi et a f . 1985; Masi and Addeo 1986; Tunick et al. 1991) and by dynamic mechanical analyses (Hsieh et al. 1993; Nolan et al. 1989; Tunick et al. 1990). The structure and flow properties of solids and fluids can be characterized by dynamic mechanical analysis, which provides information on viscoelastic properties such as storage (or elastic) modulus (G'), loss (or viscous) modulus (G") , damping (tan A), and complex viscosity (q*) (Ferry 1980; Hamann 1991; Rheometrics 1989).

Journal of Texture Studies 25 (1994) 41 1-420. All Rights Reserved. "Copyright I994 by Food & Nutrition Press, Inc.. Trumbull, Connecticut 41 1

412 J . J . Y U N . Y.L. HSIEH. D.M. BARBANO and C.L. ROHN

Rheological properties of Mozzarella cheese vary with changes in manufactur- ing variables, cheese composition, storage temperature and time (Cervantes er al. 1983; Di Matteo et al. 1982; Keller et al. 1974: Kindstedt et al. 1992; Masi and Addeo 1986; Oberg et al. 1992: Tunick et al. 1991; Yun el al. 1993d,e). Changes in manufacturing variables can affect initial cheese composition or pro- teolysis during storage, thereby affecting functional properties of Mozzarella cheese (Yun ef a/ . 1993c,d,e). As an example, the temperature used during cooking influences syneresis (moisture removal from curd) during cheese making (Van Slyke and Price 1952), which may affect curd texture.

Understanding dynamic mechanical properties of cheeses may improve our abil- ity to control functional properties of Mozzarella cheese (e.g., shredability). The objectives of this study were to characterize the dynamic mechanical properties and to determine the amount of intact protein of Mozzarella cheese to assess the effect of differences in cooking temperature.

MATERIALS AND METHODS

Cheese Making Procedure

The "no-brine" cheese making method (Yun et a/ . 1993a,d) was used to pro- duce low moisture part skim Mozzarella cheese. Raw skim milk and raw cream were obtained from Cornell University dairy plant. standardized to 2.25% fat, pasteurized at 72C for 16 s, cooled to 4C, divided into three 170 kg portions, and stored overnight at 4C. The next day, the milk (170 kg/vat) was poured into a cheese vat (Model 4MX, Kusel Equipment Co.. Watertown. WI) and heated to 36C. Direct-to-vat frozen starter culutres, Streptococcus salivanus ssp. ther- mophilus and Lactobacillus delbrueckii ssp. bulgaricus (Thermococcus C 120 and Thermorod R160, respectively, from Rhone-Poulenc. Madison, WI) were used at a rate of 0.30 mllkg of milk. Milk was ripened for 60 rnin at 36C. At the end of ripening. chymosin derived by fermentation (Chymax, double strength, Pfizer Inc., Milwaukee, WI) was added to milk at a rate of 0.10 ml/kg of milk. After rennet addition, the milk was agitated for exactly 1 rnin before set.

Following a 30 rnin set, the milk coagulum was cut with a 1.2 cm wire knife and allowed to heal for 5 min. Next, the curds were stirred gently without heat for 10 min, followed by heating from 36C to one of the 3 different cooking temperatures (i.e., 38.41, and44C) over 15 rnin with continuous agitation. The agitation continued while maintaining the specific temperatures until the whey pH reached 6.40 k 0.02. then the whey was drained and the curd was piled in the center of the vat. Curd slabs were turned (cheddared) every 15 rnin until the curd reached a milling pH of 5.25. The cheese curd was milled and salted at a total rate of 2% (w/w). Salted curd was stretched using a pilot scale Mozzarella

MOZZARELLA RHEOLOGY 413

mixer (Model 640, Stainless Steel Fabricating Co., Columbus, WI) with circulating salt water at 57C, cooled in ice water, and vacuum packaged. All cheeses were stored at 4C for 3 weeks before the analysis.

Three vats of cheese, each with a different cooking temperature, were made in one day. The cheese making was replicated on three different days. On each day, the order of cheese making for the three cooking temperatures was changed systematically to block out the effects of day and order of cheese making.

Dynamic Mechanical Analysis

Mozzarella cheese samples were cut and placed in the sample holder (parallel plate type with a radius of 12.5 mm and a gap of 2-2.5 mm) of a dynamic analyzer (Model RDA-11, Rheometrics, Inc., Piscataway, NJ). The fiber direction of the Mozzarella cheese sample was perpendicular to the parallel plates. The surface of each plate was serrated to avoid slippage. The strain sweep was performed at 22C covering a strain range of 0-20% at a frequency of 10 rad/s. Nine cheese samples (3 cooking temperatures X 3 cheese making days) were tested in duplicate. The frequency sweep was performed at 22C at a strain of 1 % covering a fre- quency range of 0.1-100 rad/s. A total of 3 samples (3 cooking temperatures x 1 cheese making day) were tested in duplicate.

Chemical Analysis

Chemical composition and the proteolytic changes during storage were analyzed using the methods described earlier (Yun et al. 1993a,e). The SDS-PAGE method was used (Yun et al. 1993a,e) to determine the amount of intact protein (i.e., a,-caseins and &casein).

RESULTS AND DISCUSSION

Strain Sweep

The average values for either G’ or G”, obtained from the strain sweep of Moz- zarella cheeses, were not affected by different cooking temperatures (Fig. 1). The values of G’ and G ” decreased with increasing percentage strain, perhaps exhibiting the breaking of cheese structure. With increasing strain, G ’ decreased faster than G”. At a strain of about lo%, G’ and G ” were about equal at around 1.6-1.7 X 105 dyne/cm2. Accordingly, tan 6 (i.e., G”/G’) increased with in- creasing percentage strain, and tan 6 was around one at about 10% strain. The elastic nature of the cheese was more dominant at a strain less than 10% while viscous nature was more important at a strain higher than 10%. The strain sweep

414 J . J . YUN. Y .L . HSIEH, D.M. BARBANO and C.L. ROHN

G' and G" of Mozzarella Cheese (Effect of Cooking Temperature)

1 .OE+07

h Y

E 9 1.OE+06 a, C h 9 b 6 1.OE+05

L CJ

1 .OE+04 0 2 4 6 8 10 12 14 16 18 ~

Strain (06)

t

44 C (G')

41 C (G')

30 C (G')

44 C (G")

41 C (G")

38 C (G")

x

-A-

- - -

t

- T

FIG. I . G ' OF MOZZARELLA CHEESES PRODUCED WITH COOKING TEMPERATUREOF 38C ( A ) . 4 1 C ( X ) . AND44C (.) A N D G " 0 F MOZZARELLA CHEESES PRODUCED WITH DIFFERENT COOKING TEMPERATURE 38C (X).

41C (+), AND 44C ( C ) IN 0-20% STRAIN SWEEP

results of other cheeses by Tunick et al. (1990) do not show the crossover at 10% strain as in the present study. However, the general decreasing trend and the magnitude of G ' and G " values were similar to those of the present study.

The values of tan 6 for all Mozzarella cheeses were between 0.3 and 0.4 at low strain (i.e., at 1 or 2 % strain). According to Hamann (1991), protein gels are normally quite elastic with the values of 6 being near 10" (tan 6 = 0.2). Ferry ( 1980) classified materials into four categories depending on the value of tan 6: (1) tan 6 is very high for dilute solution because both solvent and solute con- tribute to G ", but only the solute contributes to G '; (2) all amorphous polymers, whether cross-linked or not, have tan 6 values ranging from 0.2 to 3.0; (3) glassy and crystalline polymers have values near 0. I ; and (4) lightly cross-linked polymers have very small value of 0.001-0.01. The complex viscosity ?I* of Moz- zarella cheeses, made using all three cooking temperatures, decreased with in- creasing strain because both G ' and G " decreased with increasing strain.

Frequency Sweep

The values of G ' and G " from the frequency sweeps are shown in Fig. 2. With increasing frequency from 0.01 to 100 rad/s, G ' increased from 3 x lo5 to 1 x lo6 dyne/cm2, and GI' increased from 1 x lo5 to 4 x lo5 dyne/cm2. The values for tan 6 of all Mozzarella cheeses (at frequencies ranging from 0.1 to

MOZZARELLA RHEOLOGY 415

100 rad/s) were between 0.3 and 0.4. The magnitudes of G', G", and 11* of all cheeses from our frequency sweep experiment were similar to the values for Mozzarella obtained by Nolan ef al. (1989) at 0.5% strain and 20C. In experiments by Nolan er al. (1989) and the present one, G' was higher than G" in the fre- quency sweep (Fig. 2). This indicates that Mozzarella cheese samples from both experiments were in the plateau region of viscoelastic spectrum (Ferry 1980; Graessley 1984). This plateau region separates the short time response (i.e., tran- sition region) where the chain architecture has little effect, from the long time response (i.e., terminal region) where such features as molecular weight, molecular weight distribution, and long chain branching have a profound effect: for polymer melts and concentrated solutions, the response in the plateau region can be at- tributed to entanglement (Graessley 1984).

When comparing the vlaues of G ' and G" from frequency sweep experiment with the results of Ferry (1980), Mozzarella cheese samples were similar to lightly or very lightly cross linked amorphous polymer (lightly vulcanized Hevea rub- ber or styrene-butadiene random copolymer, respectively). The values of tan 6 for Mozzarella cheese samples were similar to those of amorphous polymers of high molecular weight below its glass transition temperature (poly methyl methacrylate) or very lightly cross linked amorphous polymer (styrene-butadiene random copolymer).

G' and G" of Mozzarella Cheese (Effect of Cooking Temperature)

l ' O E + 0 7 U --t

44 C (G')

41 C (G')

38 C (G')

- --t

-E+-

44 c (G') 41 C (G")

38 C (G") +

0.1 1 .o 10.0 100.0 Frequency (rad/s)

FIG. 2. G ' OF MOZZARELLA CHEESES PRODUCED WITH COOKING TEMPERATURE OF 38C (A), 41C (X ) , AND 44C (m) AND G"OF MOZZARELLA CHEESES PRODUCED WITH COOKING TEMPERATURE OF 38C (_a), 41C (+),

AND 44C (0) IN 0.1-100radls FREQUENCY SWEEP

416 J . J . YL". Y.L. HSIEH. D .M. B A R B A N 0 a n d C . L

U

v v

U

d v

U

co m

m

- VI 0

+ I 9

Q - 0 3

in 0 d X

N 0

+I - in in

d

- VI 0

+ I .n

0

9 v - 3

in 0 d X

N 0

A

+I - N \D

d

- .Y 0 0

+I v h - 0 3

in 0 d X

N 0

+I - m m d

I

N E u

;$ x a -

ROHN

MOZZARELLA RHEOLOGY 417

From the frequency sweep data, G ’ and G ” were transformed to interpret the data by the power-law model, i.e., P = sub, where P can be G‘ or G ” , while a and b are constants (Table 1). The mean values of the constant b for G ‘ and G ” of Mozzarella cheese in our experiment ranged from 0.16 to 0.18, similarly to the values from Nolan er al. (1989), which ranged from 0.17 to 0.19.

The Relationship Between Chemical and Rheological Properties

The similarity in viscoelastic properties of Mozzarella cheeses with three dif- ferent cooking temperatures seems to be consistent with the similarity in chemical composition. For example, moisture content of the cheeses ranged from 43.2% to 45.2%, fat content from 22.0% to 22.5%, protein content from 27.6% to 28.7%, and salt content from 1.41 to 1.44% (Yun et al. 1993d).

Since Mozzarella cheese has a protein network structure, not only the total pro- tein content but also the amount of intact protein (i.e., a,-caseins and 0-casein) present in the cheese would be important for the integrity of structure. The residual coagulant causes proteolytic changes in Mozzarella during storage (Farkye et al. 1991; Yun et al. 1993b). Chymosin (the coagulant used in this experiment) preferentially hydrolyzes as-caseins to smaller peptides while leaving 0-casein intact according to the SDS-PAGE analysis (Yun 1993a,b,d). The percentages of intact as-caseins and 0-casein (Table 2 ) remaining in the cheeses after 2 weeks of storage at 4C were similar, showing little effect of cooking temperature used in this experiment.

In a related study (Yun 1993d), when the storage was extended to 7 weeks, the amount of proteolysis became significantly different among the cheeses pro- duced with different cooking temperatures. However, during the time of storage (at 4C) generally considered optimum for use in pizza (i.e., 1-3 weeks), no signifi-

TABLE 2.

CHEESE PRODUCED WITH DIFFERENT COOKING TEMPERATURES AND STORED AT 4C FOR 2 WEEKS (MEAN f STANDARD DEVIATION)

THE PERCENTAGE OF INTACT aS-CASEIN AND &CASEIN IN MOZZARELLA

Cooking Temperatures Intact Casein as a Percentage of Total Protein

38 c 4 1 C 44 c

0,-caseins ( % I 38.0 2 1 . 0 3 9 . 5 & 4 . 2 3 8 . 3 2 4 . 6

!3-casein ( % ) 3 4 . 7 5 1 . 6 3 4 . 2 5 0 . 7 3 3 . 9 2 1 . 6

418 J . J . YUN. Y.L. HSIEH. D.M. BARBANO and C.L. ROHN

cant differences in proteolysis among the cheeses were observed (Table 2). This may be the reason why the viscoelastic properties of the cheeses were similar.

These results indicate that there may be an interrelationship among chemical composition, proteolysis, and rheological properties of Mozzarella cheese. However, to confirm the interrelationship, statistical analysis (correlation) needs to be applied on the data set showing larger variations in each of the parameters. Thus, in future studies, it would be useful to measure the viscoelastic properties of Mozzarella cheese that differ in proteolysis.

CONCLUSIONS

The differences in cooking temperatures (38, 41, and 44C) during cheese manufacturing showed little effect on G', G", v*, or tan 6 of Mozzarella cheese stored for 3 weeks at 4C and tested at 22C. The values of G, G ' and tan 6 of Mozzarella cheeses were 5.8 - 6.4 x lo5 dyne/cm2, 1.9 - 2.1 X lo5 d yne/cm2, and 0.33 - 0.35, respectively at 1 % strain and 10 rad/s. The intact protein con- tents (i.e.. cus-caseins and 0-casein) in all cheeses were also similar. The percen- tages of intact a,-casein and 0-casein were 3 8 4 0 % and 33-35% of total protein in the cheese, respectively.

ACKNOWLEDGMENTS

The authors thank Dr. S. Mulvaney for arrangement of dynamic mechanical analysis, and R. Rasmussen, W. Tsai, and G. Houghton for their technical assistance. Financial support was provided by Northeast Dairy Foods Research Center.

REFERENCES

CASIRAGHI, E.M., BAGLEY, E.B. and CHRISTIANSON, D.D. 1985. Behavior of Mozzarella, Cheddar and processed cheese spread in lubricated and bonded uniaxial compression. J . Texture Studies 16, 281-301.

CERVANTES, M.A., LUND, D.B. and OLSON, N.F. 1983. Effects of salt con- centration and freezing on Mozzarella cheese texture. J . Dairy Sci. 66.

DI MATTEO, M.G.. CHIOVITTI, M.G. and ADDEO, F. 1982. Changes in Mozzarella cheese composition at different conditions of storage. Sci. Tec. Latt. Cas. 32. 197-213.

204-213.

MOZZARELLA RHEOLOGY 419

FARKYE, N.Y., KIELY, L.J., ALLSHOUSE, R.D. and KINDSTEDT, P.S. 1991. Proteolysis in Mozzarella cheese during refrigerated storage. J. Dairy Sci. 74, 1433-1438.

FERRY, J.D. 1980. Viscoelastic Properties of Polymers, 3rd Ed., pp. 41-47, 501-508, John Wiley & Sons, New York.

GRAESSLEY, W.W. 1984. Viscoelasticity and flow in polymer melts and con- centrated solutions. In Physical Properties of Polymers, (J.E. Mark, A. Eisenberg, W.W. Graessley, L. Mandelkern, and J.L. Koenig, eds.) pp. 107-1 1 l) , ACS, Washington, DC.

HAMANN, D.D. 1991. Rheology: A tool for understanding thermally induced protein gelation. In Inferaction of Food Proteins, (N. Parris and R. Barford, eds.) pp. 212-227, ACS Symp. Ser. 454, ACS, Washington, DC.

HSIEH, Y.L., YUN, J.J. and RAO, M.A. 1993. Rheological properties of Moz- zarella cheese filled with dairy, egg, soy proteins, and gelatin. J. Food Sci.

KELLER, B., OLSON, N.F. and RICHARDSON, T. 1974. Mineral retention and rheological properties of Mozzarella cheese made by direct acidification. J. Dairy Sci. 57, 174-180.

KINDSTEDT, P.S., KIELY, L.J. and GIdMORE, J.A. 1992. Variation in com- position and functional properties within brine salted Mozzarella cheese. J. Dairy Sci. 75, 2913-2921.

MASI, P. and ADDEO, F. 1986. An examination of some mechanical proper- ties of a group of Italian cheeses and their relation to structure and conditions of manufacture. J. Food Eng. 5 , 217-229.

NOLAN, E.J., HOLSINGER, V.H. and SHIEH, J.J. 1989. Dynamic rheological properties of natural and imitation Mozzarella cheese. J. Texture Studies 20,

OBERG, C.J., MERRIL, R.K., BROWN, R.J. and RICHARDSON, G.H. 1992. Effects of milk-clotting enzymes on physical properties of Mozzarella cheese. J. Dairy Sci. 75, 669-675.

TUNICK, M.H., MACKEY, K.L., SMITH, P.W. and HOLSINGER, V.H. 1991. Effect of composition and storage on the texture of Mozzarella cheese. Neth. Milk Dairy J. 45, 117-125.

TUNICK, M.H., NOLAN, E.J., SHIEH, J.J., BASCH, J.J., THOMPSON, M.P., MALEEFF, B.E. and HOLSINGER, V.H. 1990. Cheddar and Cheshire cheese rheology. J. Dairy Sci. 73, 1671-1675.

Rheometrics. 1989. Understanding Rheological Testing, pp. 15-17, Rheometrics, Piscataway, New Jersey.

VAN SLYKE, L.L. and PRICE, W.V. 1952. Cheese, pp. 171-173, Orange Judd Publ. Co., New York.

58, 1001-1004.

179- 189.

420 J . J . YUN. Y.L. HSIEH. D.M. BARBANO and C.L. ROHN

YUN, J.J., BARBANO. D.M. and KINDSTEDT, P.S. 1993a. Mozzarella cheese: impact of milling pH on chemical composition and proteolysis. J. Dairy Sci.

YUN, J.J., BARBANO. D.M. and KINDSTEDT. P.S. 1993b. Mozzarellacheese: impact on coagulant type on chemical composition and proteolysis. J. Dairy Sci. 76, 3648-3656.

YUN, J .J . , KIELY, L.J., BARBANO, D.M. and KINDSTEDT, P.S. 1993c. Mozzarella cheese: impact of milling pH on functional proeprties. J . Dairy Sci. 76. 3639-3647.

YUN, J.J.. KIELY, L.J., BARBANO, D.M. and KINDSTEDT, P.S. 1993d. Mozzarella cheese: impact of cooking temperature on chemical composition, proteolysis. and functional properties. J . Dairy Sci. 76, 3364-3373.

YUN. J.J., KIELY, L.J., KINDSTEDT. P.S . , and BARBANO, D.M. 1993e. Mozzarella cheese: impact of coagulant type on functional properties. J. Dairy Sci. 76. 3657-3663.

76, 3629-3638.