Caseinolytic Activity of Micrococci Isolated from Cheddar Cheese

Micrococci counts of Cheddar cheese, plated throughout ripening, never exceeded 10×103 and, after 3.5 months of ripening, few micrococci (less than 10×l02) grew on the selective tryptone agar medium. Eighteen micrococci were isolated from 5 lots of cheese at various times during ripening. Three of these formed extracellular proteinase which hydrolyzed preferentially αs-casein. Intracellular extracts from all isolates degraded preferentially the β-casein moiety of isoelectric casein. Casein hydrolyzates did not stimulate acid production by a Cheddar cheese Lactobacillus isolate. β-Casein component of micellar or isoelectric casein was degraded rapidly by the intracellular extracts. However, proteinase(s) did not hydrolyze purified β-casein as rapidly. Apparently, fractionation and purification modify β-casein such that resistance to proteolysis is imparted.