a method for manufacturing reduced fat mozzarella cheese

A Method for Manufacturing Reduced Fat Mozzarella Cheese'

RICHARD K. MERRILL, CRAIG J. OBERG,2 and DONALD J. McMAHON Western Center for Dairy Protein Research and Technology

Department of Nutrition and Food Sciences Utah State University

Logan 84322-8700

ABSTRACT

Mozzarella cheese was manufactured to contain up to 50% less fat than conventional part-skim Mozzarella cheese. Milk, which had been standardized to a casein to fat ratio of 1.2, 1.6, 2.0, or 2.4, was inoculated with single strains of Lactobacillus helveticus and Streptococ- cus salivanus ssp. themphilus. A new manufacturing procedure was used to retain moisture in the cheese as at percentages decreased and protein increased. Stretch, melt, and cook color were evalu- ated at 1, 7, 14, and 28 d during storage at 4'C. Analysis of variance showed no significant differences in stretch, melt, or cook color between cheeses with different casein to fat ratios. Cheese made with a casein to fat ratio of 2.4 retained more stretch over 28 d than did cheese with lower casein to fat ratios. Stretch decreased and melt increased significantly for all cheeses during storage for 28 d. The stretch and melt characteristics of Mozzarella cheese containing up to 50% less fat were similar to the part- skim Mozzarella reference cheese. (Key words: Mozzarella cheese, reduced fat, physical properties)

Abbreviation key: C:F = Ratio of casein to fat.

Received May 24, 1993. Accepted February 18, 1994. 1Contribution Number 4392 of the Utah Agriculture

Experiment Station. Approved by the director. Mention of companies or products does not constitute endorsement by Utah State University, Utah Agricultural Experiment Sta- tion, or Weber State University over similar products not mentioned.

ZDepartment of Microbiology, Weber State University. Ogden, UT 84408-2506.

INTRODUCTION

Production of Italian cheese varieties (Moz- zarella, Provolone, Ricotta, Romano, and Parmesan) in the United States increased in 1991 to 1.1 billion kg; Mozzarella cheese ac- counted for 78% of the total Italian cheese production (USDA Statistical Research Serv- ice, Washington, DC, 1992, personal commu- nication). Reduced fat, lowfat, and nonfat dairy products are becoming more prevalent in the dairy industry. However, decreasing or removing fat from cheese changes physical and fla- vor characteristics, which often reduces quality. Brown (3) found that decreasing the amount of milk fat results in a cheese that is very hard and tough. Reduced fat Mozzarella cheeses manufactured to date typically have less than 30% of the milk fat removed. Removal of more milk fat usually results in very tough curd and poor melt and stretch properties (3).

Modification of the protein or fat percent- age of Mozzarella cheese made with recom- bined milk also reduces stretch and melt (11). The cohesiveness and hardness of Mozzarella cheese made with retentate-supplemented milk were similar to those of conventional Moz- zarella cheese (7, 8). Creamer and Olson (6) attribute changes in cheese body and texture to the endopeptidases that cleave a-casein. Con- centrations of as-casein were higher in Moz- zarella cheese than in Gouda or Cheddar (5). The ratio of peptidase activity to protease activity is higher in Lactobacillus helveticus than in Lactobacillus delbrueckii ssp. bulgaricus (10). This ratio affects the rates of change in the textural properties of cheese (16).

The physical properties of Mozzarella cheese depend on cheese age, pH, calcium, moisture, fat, salt content, and the starter culture (4, 13, 14, 19, 20, 21, 24). When moisture or fat on a dry basis increases, Mozzarella cheese becomes softer and less shreddable (9, 17). When direct acidification is used instead

1994 J Dairy Sci 77:1783-1789 1783

1784 MERRILL ET AL

of starter cultures, the physical properties of Mozzarella cheese depend on the type of acid used and final curd pH.

After numerous preliminary trials were conducted for making a reduced-fat Mozzarella cheese, the manufacturing procedure described in this paper was selected as the best method to retain moisture in the cheese and to reduce its tough and rubbery characteristics. We then assessed the effects of reducing milk fat content on the stretch, melt, and cook color of Mozzarella cheese in manufacturing a reduced fat Mozzarella cheese acceptable for use on pizza.

MATERIALS AND METHODS

Milk and Cultures

Milk from the Utah State University Dairy Products Laboratory was pasteurized at 80'C for 29 s and then cooled overnight to 4'C. Milk was standardized to a casein to fat ratio (C:F) of 1.2, 1.6, 2.0, or 2.4. Milk was standardized by blending whole and skim milks of known fat and protein concentrations in ap- propriate proportions to give the desired C:F. Three milliliters of single strength calf chymo- sin (Lacto-Labo; Rhbne-Poulenc, Dange Saint- Romain, France) was diluted with 50 ml of cold water prior to use. Direct-set lyophilized culture, consisting of L helveticus LHlOO and Streptococcus salivarius ssp. themphilus TA06 1 (L.acto-Labo), were individually weighed into sterile test tubes and stored at 4C until used.

Mozzarella Manufacturing Procedure

Seven liters of milk were placed into each of four stainless steel vats (21.6 x 21.6 x 21.6 cm). The 1.2 C:F milk was used to make a reference cheese with a fat content typical of part-skim Mozzarella cheese. The other three batches of milk were used to make a gradient of cheeses with fat contents lowered to 50% of part-skim Mozzarella cheese. Three batches of milk (standardized to C:F of 1.6, 2.0, and 2.4) were then acidified to pH 6.0 with 80% lactic acid diluted 1:2 (vol/vol) with distilled water. All four cheese vats were placed in a water bath, and the milk was warmed to 33.9'C. Each vat was inoculated with .75 g of each

Journal of Dairy Science Vol. 77, No. 7, 1994

culture and allowed to ripen 45 min at 33.9"C. Fifty milliliters of diluted rennet were added to the milk. The three reduced fat curds (C:F of 1.6, 2.0, and 2.4) were cut 10 min after rennet addition using 1.9-cm knives, and the reference batch (C:F 1.2) was cut 50 min after rennet addition. After cutting, each vat was left undisturbed for 15 min, followed by 30 s of gentle agitation every 15 min. The curd was heated to 37.8'C over 10 min and was held at that temperature until the whey titratable acidity reached .17; then the whey was drained. Cheese curd was then cheddared by manually rotating curd patties every 20 min; curd blocks were piled two deep on the first turn. When titratable acidity reached .60, the curd was hand molded and stretched in fresh 82C water until the molten curd was smooth and elastic (approximate time, 2.5 min). Molded curd was placed in a stainless steel box (8.9 x 8.9 x 8.9 cm) and set in an ice bath to form a small loaf. Blocks of cheese were then placed in a saturated NaCl brine for 4 h at 4'C. Each cheese was individually vacuum- packaged and stored at 4C until tested. After samples were removed, each cheese was vacuum-sealed again. Three cheeses were made at each of the C:F.

Chemical and Physical Analysis of Cheese

Cheese was analyzed for moisture using the CEM microwave oven (Model AVC 80; CEM Corp., Matthews, NC), and fat was determined using a modified Babcock method (25) 1 d after manufacture. Samples were analyzed for melt by the modified tube test (22). and cook color was determined by reflectance colorime- try (26). Melt and cook color methods were modified as previously described (19). Samples were tested at 1, 7, 14, and 28 d of storage.

Stretch Test

Stretch was determined using a modified version of the helical viscometer method of Kindstedt et al. (15). Fifteen grams of shredded cheese were tamped into a 25-rnm x 150-mm test tube and tempered in a 60C water bath for 10 min. A Brookfield DV 11+ (Brookfield Engineering Laboratories, Inc., Stoughton, MA) helipath viscometer fitted with a T-bar spindle (?F with a 1.075 cm crossbar)

PHYSICAL PROPERTIES OF MOZZARELLA CHEESE 1785

TABLE 1. Mean percentages of fat, fat on dry basis OB). moisture, and moisture in the fat-free substance (MFFS) for Mozzarella cheese made at different casein to fat ratios (CF).

C:F Fat FDB Moisture MFFS

- (96) - - X SEM X SEM R SEM X SEM

1.2 19.3 .58 41.7 1.16 53.7 .09 66.6 .67 1.6 15.0 1.0 31.5 1.86 52.4 .88 61.7 1.66 2.0 12.3 5 8 25.4 1.41 51.4 .61 58.6 .52 2.4 10.3 .58 22.0 .% 47.0 .68 52.4 1.21

was gradually submerged in the tempered cheese until it reached the bottom. The helipath stand was then turned off, and the viscometer was adjusted to a speed of 1.5 rpm, a full-scale reading was attained, and the helipath stand was turned on. An IBM- compatible computer, equipped with DV Gather+ version 1.0 (Brookfield Engineering Laboratories, Inc., Stoughton, MA), was used to take 120 readings, one every 5 s, while the helipath raised the viscometer spindle out of the tube. Relative peak areas were derived for each 10-min measurement period. Readings greater than 100 were adjusted to 100 when relative peak areas were calculated.

Statistical Analysis

The cheeses were made and tested using a randomized block design with repeated meas- ures. Analyses of variance, conducted as a split plot in time, were run separately for the depen- dent variables cook color, melt, and stretch. There were three independent replicates for each C:F. Correlations, means, and analyses of variance were calculated using Jmpm software from SAS@ (12). Because time cannot be randomized, this design could also be analyzed as a split plot in C:F (i.e. two pseudo main plots). Therefore, separate error terms (A, B, and C) were used to determine significance of C:F, time, and C:F by time interactions, respec- tively.

RESULTS

Cheese Manufacture

Mozzarella cheese produced at each of the C:F exhibited normal characteristics. A reduced fat Mozzarella cheese with charac-

teristics comparable with those of a part-skim Mozzarella cheese (20, 21) was made with modifications in the manufacturing procedure. These changes in manufacturing procedures included an elevated pasteurization temperature (80'C for 29 s), preacidification of milk to pH 6.0 prior to setting with rennet, larger cutting knives, reduced cooking temperature (37.8'C), periodic agitation during cooking instead of constant stimng, and less frequent turning during cheddaring. Other processing methods that were tried without success at retaining moisture in the curd included removing the curd at a high pH (low titratable acidity), reducing the cook temperature to 35.5'C, and removing whey followed by addition of water during cooking.

However, reduction in the amount of fat produced cheeses that had a greenish tint, ap- parently because of fewer light-scattering centers in the cheese. Moisture in the reduced fat cheeses ranged from 47.0 to 52.4% and fat from 10.3 to 15.0% (Table 1) The reference cheese had higher moisture than usual because it was made using the modifications (such as shorter manufacturing time, elevated pasteurization temperature, and lower cook temperature) to retain moisture in the lower fat cheeses.

Stretch

Reduced fat Mozzarella cheeses showed a significant decrease in stretch over time (Table 2). No significant difference in stretch occurred between reduced fat cheeses and the part-skim Mozzarella reference cheese. The decrease in stretch in all four cheeses was greatest during the first 7 d of storage (Figure 1). Cheese made with a C:F of 2.4 (lowest fat and highest


1786 MERRILL ET A L

TABLE 2. Analysis of variance for stretch, melt, and cook color in Mozzarella cheese made at four different casein to fat rations (C:F).

MS

Source of variation df ~~

Stretch Melt Color

Replicate (Rep) C:F C:F x Rep (error A) Time Time x Rep (error B) Time x C:F C:F x Time x Rep (error C) Corrected total

2 3 6 3 6 9

18 47

WOY 1.08Ns ' 1 ~07Ns 8.08NS 1.33" 2.5oNs 9.8gNS 1.65 .83 4.78

87.37"' 24.38*** 61.35*** .46 .81 2.73

2.47NS 1.69** 2.36Ns 1.04 .33 2.23

1Not significant (P = .05). * P = .05. **P = .01. ***P = ,001.

protein) showed the least reduction in stretch over the 28-d of storage.

Melt

Cheese made with a C:F of 1.2 showed the largest increase in melt during the first 7 d and had the greatest melt from d 7 through 28 (Figure 2). Melt increased throughout storage in all of the cheeses. Overall there was no significant difference in melt between cheeses made at different C:F, although there were some differences at various storage times (Ta- ble 2). Melt was significantly affected by time, and the time by C:F interaction was signifi-

cant, suggesting a difference in the way the cheeses aged during storage. The melt of the 1.2 C:F reference cheese increased after 7 d of storage and then remained constant through 28 d. In contrast, the melt of lower fat cheeses increased gradually over 28 d.

Cook Color

Cook color for all cheeses increased stead- ily during storage (Figure 3), particularly between d l and 14. No significant differences existed in cook color between cheeses of different C:F, but a significant difference was found over time (Table 2).

I 7 14 ?X Time (d)

Figure 1. Mean (HEM) stretch measurements (relative peak area) of Mozzarella cheese made from milk with a casein to fat ratio of 1.2, solid bar; 1.6, dark Striped bar, 2.0, open bar; and 2.4, light striped bar.

I 14 28 Time (d)

Figure 2. Mean melt &EM) measurements (cen- timeters) of Mozzarella cheese made from milk with a casein to fat ratio of 1.2, solid bar; 1.6, dark striped bar; 2.0, open bar; and 2.4, light striped bar.


PHYSICAL PROPERTES OF MOZZARELLA CHEESE 1787

I 14 ?X ' Time (dl

Figure 3. Mean &SEW cook color measurements of Mozzarella cheese made from milk with a casein to fat ratio of 1.2. solid bar; 1.6, dark striped bar; 2.0, open bar; and 2.4, light striped bar. b* = Yellow-blue on a Hunter Lab colorimeter.

DISCUSSION

A number of changes in the manufacturing procedure were used to retain moisture and to maintain the desirable physical properties in reduced fat Mozzarella cheese. An elevated pasteurization temperature was used to dena- ture some whey proteins, which are then trapped in the curd matrix and aid in water retention (23). Preacidification of milk prior to rennet addition was used to decrease clotting time. A shorter coagulating time means the curd can be cut more quickly, helping to trap additional water and to increase moisture retention (2). Reduced cooking temperature, larger cutting knives, and periodic agitation were used to create larger curd particles, thus decreasing syneresis and improving moisture retention in the curd during cooking. Periodic, rather than continuous, agitation was also im- portant for reducing curd shattering because the larger curd particles were more susceptible. Less frequent turning during cheddaring kept the curd on top cool, slowing acid development. Slower acid development decreased rate of whey expulsion, thereby retaining moisture in the curd. The difficulty in retaining moisture in reduced fat cheeses is well demonstrated in Table 1; even with these changes, the reduced fat cheeses still had lower moisture contents than the control cheese.

Some studies have attributed beneficial effects to pairing L. helveficus with S. salivari- ous ssp. thernwphilus. Strains of L. helveficus also exhibit greater peptidase activity than

strains of L. delbrueckii ssp. bulgaricus (10). Ardo and Pettersson (1) studied the production of a lowfat, semi-hard cheese and found that addition of heat-treated L. helveticus enhanced the peptidolytic activity during the first few weeks, which they attributed to an aminopepti- dase from the L. helveticus cells. This higher peptidolysis, coupled with the reducing sugar available in Mozzarella cheese, suggested an increase in cook color for cheese made with L. helveticus. Mozzarella cheese made with single strains of L. heIveticus actually showed a decrease in cook color, and cook color increased with time for cheese made with paired strains of proteinase-positive L. helveticus and S. salivanus ssp. themphilus (20). As increasingly more fat is removed, Moz-

zarella cheese becomes tougher and more difficult to melt. This increased toughness of the reduced fat cheeses can be related to the increased protein concentration of such cheeses and distribution of moisture in the cheese matrix. Studies of the microstructure of Moz- zarella cheese (18) showed that much of the water, rather than being distributed evenly throughout the cheese, is contained in columns between protein fibers. Also, within these columns are the emulsified fat droplets, which prevent the protein strands from coalescing.

These protein strands were observed by Oberg et al. (18) to be homogeneous in appear- ance; thus, the moisture content of these strands is assumed to be a function of the water-binding capacity of the proteins. Conse- quently, as fat is removed, these columns would become more narrow, and the moisture content of the cheese would be reduced ac- cordingly. It could be hypothesized that the moisture content (expressed as moisture in the fat free substance) would reach a minimal level based solely on water-binding capacity of the proteins. Inclusion of denatured whey proteins in the cheese would then allow more moisture to be retained in the cheese, as occurred in this study. In some earlier trials, we were able to produce reduced fat Mozzarella with high ini- tial moisture contents, but large amounts of whey leakage continued after the cheese was packaged. This result suggests that the protein fibers continued to coalesce and that water was being forced out of the fat and water columns until the solid fat droplets were sufficiently closely packed and the columns could not be compacted any further.


1788 MERRILL ET AL

The difficulty in melting reduced fat Moz- zarella cheese has been observed by other researchers. Mozzarella cheese made with elevated moisture and fat on dry basis becomes soft and difficult to shred (9, 17). High moisture Mozzarella made from reconstituted NDM also has poor body characteristics (9). Tunick et al. (27) reported that Mozzarella cheese made with lower fat and moisture was too hard and showed decreased meltability. In addition, the lowfat, high moisture Mozzarella was comparable with part-skim Mozzarella reference cheese only after 6 wk of refrigerated storage.

In this study, Mozzarella cheese was manufactured with reduced fat, increased protein, and using L. helveticus instead of L. defbrueckii ssp. bulgaricus in the starter culture. Throughout the 28 d of storage, all cheeses in this study decreased in stretch and increased in melt; the majority of change occurred in the first 7 d. These two measurements were strongly correlated, each being affected differently by proteolysis during the first 7 d of storage (19, 21). The comparable performance between reduced fat Mozzarella and part-skim Mozzarella in this study shows that an acceptable reduced fat Mozzarella cheese may be possible without the addition of fat substitutes.

CONCLUSIONS

A method was developed at Utah State University for the manufacture of reduced fat Mozzarella cheese that contained only 50% of the fat content of part-skim Mozzarella. Ac- cording to the new FDA food regulations, cheese with a 25% lower fat content is classi- fied as reduced fat and cheese with 50% less fat as lowfat. Although the reduced fat cheeses were more translucent, cheese made using this method had melt and stretch properties similar to part-skim Mozzarella cheese. Other properties, such as shreddability, formation of free oil, surface drying, and burning, must be ex- amined to determine suitability of this cheese for commercial pizza manufacture. Further work is also needed to scale the process to commercial levels.

ACKNOWLEDGMENTS

We thank the National Dairy Promotion and Research Board for funding this research and Donald V. Sisson for his assistance with statistical analysis.

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PHYSICAL PROPERTIES OF MOZZARELLA CHEESE 1789

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a method for manufacturing reduced fat mozzarella cheese

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