Optimization of Lactic acid bacteria starter culturing and freezing conditions

Response surface methodology was used to optimize the MRS-based culture medium for Lactobacillus bulgaricus and Streptococcus thermophilus culturing, also the best freezing-dried protectors were studied. The experiment shows that Na2CO3 solution was added continuously to keep lactobacillus bulgaricus pH around 5.8, streptococcus thermophilus pH around 6.4. By fermentation with 15h, the lactobacillus bulgaricus concentration can reach 1.24×109cfu/mL and Streptococuus thermophilus with 8.05×108cfu/mL. The collected bacteria by centrifugal separation was freezing-dried at -51℃, vaccum value 9Pa, 24h, at last the living bacteria amount can reach 1.43×1010cfu/g.