Study on high cell density culture conditions of DVS yogurt starter cultures

Lactobacillus bulgaricus L.b-23 and Streptococcus thermophilus S.t-14,which had been isolated and identified in our laboratory,were used for the production of DVS yogurt starter cultures.The optimum fermentation condition was studied.For strains L.b-23:S.t-14 of 1:1,pH varied from 6.6～6.8,shaker's rotating speed 85～100r/min,42℃ for 18h,the cell population was up to 1.27×109cfu /mL.The cryoprotectants consisting of trehalose (1.8%),glycerin (0.25%),glutamate-Na (5.5%) and Tween 80 (0.5%) was added to the suspension.Owing to the cryoprotectants produced a very positive effect on promoting the viability of the paired strains L. b-23-S.t-14,the cells of the production were 3.35×10 11 cfu/g after freeze-drying treatment.