Variations in fermentative activity of Streptococcus thermophilus before and after lyophilization

Effects of different protectors on the survival of S.thermophilus ST-2 during lyophilization were studied.Furthermore,variations in fermentative activity of S.thermophilus ST-2 around lyophilization were examined.The results indicated that different protectors exerted significantly effects on the cells freeze dried survival rate and the viable cells number of freeze dried starter (P 0 01).Compound protectorⅡ was the favorable protective additive for the cells survival during lyophilization,for instance,it could make the cells freeze dried survival rate reach 97 27% and the viable cells number of freeze dried starter reach 3 22×1010 g-1.To study the effects of starter lyophilization,freeze dried starter obtained by compound protectorⅡ,fermented in milk medium for 12 hours at 42 ℃,did not vary obviously in the curves of cells growth,produced acidit and reduced pH.The experiments showed that freeze dried starter obtained by the optimm protectors could use as direct vat inoculation starter.