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A. J. PASTORINO¹, N. P. Ricks, C. L. Hansen, and D. J. McMahon. (1) Western Dairy Center, Dept. of Nutrition and Food Sciences, Utah State University, Old Main Hill 8700, Logan, UT 84322-8700

JUSTIFICATION: Differences in cheese microstructure are thought to play a role in explaining differences in functional properties of cheese.

OBJECTIVES: Our objective was to study the influence of water and calcium injection on the microstructure, hardness, cohesiveness, adhesiveness, springiness, and melting of Mozzarella cheese.

METHODS: Mozzarella cheese (53% moisture, 22% fat) was made according to a direct-acid, stirred-curd procedure. Cheese was cut into 0.3 to 0.4-kg blocks, vacuum packaged and stored for 10 d at 4°C. Cheese blocks were then injected from 1 to 5 times, using a high-pressure injection system with either water or a 40% calcium chloride solution. Successive injections were performed 24-h apart. After 42 d of storage at 4°C, cheese blocks were analyzed for structural and functional attributes.

RESULTS: When water was injected, an increase in weight was observed (1 to 1.5%). Moisture content increased (0.5 to 2.7 percent units), whereas the pH was unaffected. In scanning electron micrographs the control cheese had the typical structure of a stirred-curd cheese: protein interspersed with areas containing fat or serum. Injecting water increased the area occupied by protein (~14% at the highest level). Water injection did not affect cohesiveness, adhesiveness, springiness, or melting. However, it decreased hardness. In contrast, when calcium was injected a decrease in weight was observed (1.8 to 11.7%) that was manifested through syneresis. Moisture content decreased (0.4 to 9.3 percent units) as well as pH. Calcium injection decreased the area occupied by protein in electron micrographs (~17% at the highest level). Cohesiveness was lowered, whereas hardness increased. Adhesiveness and springiness were unaffected. Melting decreased (~70% at the highest level).

SIGNIFICANCE: We concluded that adding calcium to cheese alters how the proteins interact, which is manifested as changes in cheese microstructure. Such changes in structure provide an understanding of changes in functional attributes of cheese.