Temperature effect on structure-opacity relationships of nonfat mozzarella cheese

Our objective was to determine the effect of heating on the structure of nonfat Mozzarella cheese and then to relate changes in structure to changes in cheese opacity. Cheese was made according to a direct-acid, stirred-curd procedure. Cheese samples, at 4 degrees C, were taken on d 1 and placed into glass bottles, which were sealed and heated. Once the cheese reached 10 degrees C or 50 degrees C, the bottles were placed on a scanner and color values measured. Samples were also taken on d 1 for chemical, micro, and ultrastructural analyses. Applying heat increased cheese opacity. At 50 degrees C the cheese was more opaque than at 10 degrees C. The increase in temperature induced changes in cheese structure. Larger high-density protein aggregates and increased protein concentration in the protein matrix were observed in cheese at 50 degrees C. Applied heat would favor hydrophobic interactions, and possibly, re-association of beta-casein and calcium with the protein matrix, promoting protein-to-protein interactions. Thus, the protein matrix contracts, occupying less cheese matrix area, and microphase separation occurs, causing serum pockets to grow in size, and microstructural heterogeneity to increase. It is proposed that the increased size of aggregates and heterogeneity of the cheese at 50 degrees C promote light reflection, thus increasing cheese opacity. We concluded that applying heat alters protein interactions in the cheese matrix, manifested as changes in cheese structure. Such changes in structure help provide an understanding of changes in cheese opacity.