Abstract: Using acid producing bacteria-Lactococcus lactis ssp. cremoris which is often used in cottage cheese making as research object, the growth characteristics of Lactococcus lactis ssp. cremoris strain CH5 in reconstituted skim milk (RSM) and changes of starter activity under 4℃ during storage were studied with three factors including CFU, pH and titrable acidity. The results showed that: the lag phase of strain CH5 in RSM was very short, the population of viable cell of which could reach 109CFU/ml; in the stationary phase. The doubling time for growth (Tdg) was about 1.03h and doubling time for lactic acid production (Tda) was about 2.87h, showed the efficient cell growth, not the acid production, a desirable property during bulk culture preparation. During storage under 4℃, the maximum acidification rate (μacid) appeared on 3d, and the viable cell counts and μacid did not show significant changes before 11d. It suggested that the mother culture prepared by CH5 strain could be maintained per 11d, and the optimum stage for bulk culture started from the 3rd day of cold storage.

Key words: Lactococcus lactis ssp. cremoris, CFU, growth curve, generation time, maximum acidification rateμacid