FATE OF COLIFORMS IN YOGURT, BUTTERMILK, SOUR CREAM, AND COTTAGE CHEESE DURING REFRIGERATED STORAGE1

Aerobacter (Enterobacter) aerogenes and Escherichia coli were inoculated separately into commercially produced samples of yogurt, buttermilk, sour cream, and cottage cheese. Inoculated products were stored at 7.2 C and were tested daily for up to 10 days to determine changes in numbers of coliforms and in pH values. The number of viable coliforms in yogurt declined dramatically and was markedly different from the initial value after only 24 hr of storage. Usually, survival of coliforms in yogurt did not exceed 3 days of holding. In buttermilk, most often a marked decline in numbers of coliforms was evident after 24 hr of storage. A substantial reduction in numbers (>50% of organisms present initially) of A. aerogenes B199 occurred in sour cream during the first 24 hr of storage, but a similar decline in numbers of E. coli and A. aerogenes FD was not evident until after 3 days of storage. Changes in numbers of E. coli and A. aerogenes in cottage cheese generally were not as rapid as in other products durin...