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Caseinolytic Activity of Micrococci Isolated from Cheddar Cheese

Department of Food Science, Cornell University, Ithaca, New York 14850

ABSTRACT

Micrococci counts of Cheddar cheese, plated throughout ripening, never exceeded 10 x 10³ and, after 3.5 months of ripening, few micrococci (less than 10 x 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 _s-casein. Intracellular extracts from all isolates degraded preferentially the ß-casein moiety of isoelectric casein. Casein hydrolyzates did not stimulate acid production by a Cheddar cheese Lactobacillus isolate.

ß-Casein component of micellar or isoelectric casein was degraded rapidly by the intracellular extracts. However, proteinase(s) did not hydrolyze purified ß-casein as rapidly. Apparently, fractionation and purification modify ß-casein such that resistance to proteolysis is imparted.