Reversibility of the temperature-dependent opacity of nonfat mozzarella cheese

Salted and unsalted nonfat mozzarella cheese was made by direct acidification and stored at 4 degrees C over 60 d. Changes in cheese opacity were measured by using reflectance L* values while the cheese was heated from 10 to 90 degrees C, then cooled to 10 degrees C, and reheated to 90 degrees C. A characteristic opacity transition temperature (T(OP)) was obtained for each cheese. Both salt content and storage time influenced T(OP). Opacity during heating, cooling, and reheating formed a hysteresis. At d 1, the unsalted cheese became opaque when heated to 20 degrees C, but the salted cheese required heating to 40 degrees C. As the salted cheese was aged, its T(OP) increased so that by 60 d the cheese did not become opaque until it was heated to 70 degrees C.