Effects of Aging Time and Temperature on Proteolysis of Commercial Goat Milk Cheeses Produced in the United States

We evaluated the effects of aging time and temperature on proteolytic indices of freshly prepared commercial cheeses from goat milk. Five varieties of cheeses from goat milk (plain soft, pepper soft, Caciotta, Monterey Jack, and raw milk Cheddar) and two from cow milk (one fresh and one 2-mo-old Cheddar) were collected from four different manufacturers located in Texas and Wisconsin. Two replicates of the seven varieties of the cheeses were assigned to three temperatures (4, 13, and 22C) and six storage periods (0, 2, 4, 8, 16, and 24 wk) in a 7 x 3 x 6 factorial arrangement. For all samples, indices of proteolysis were determined: the ratio of watersoluble N to total N and the ratio of 9.6% TCA-soluble N to total N. Hydrolysis and degradation of casein moieties of the cheeses during the 6-mo ripening were determined by PAGE; pH and ADV were also determined. Percentages of water-soluble N in all cheese varieties were doubled after 2 wk of aging at 4C. Soluble N (water-soluble N and TCAsoluble N) contents steadily increased as aging time and temperature increased for all cheeses, with some variations. pH, water-soluble N, and TCA-soluble N of soft cheeses were lower than those of hard varieties throughout the experimental period. The acid degree values were synergistically elevated by aging time and temperature, and those of the pepper