Study On The Production Method Of High Concentrate Yoghurt Starter By Vacuum Freeze Drying

This paper mainly dealt with the culture conditions of Lactobacillus bulgaricus and Streptococcus thermophillus. The culture conditions of Lactobacillus bulgaricus were : culture temperature 40℃, initial pH value 5.80, plain culture, culture time 12h; the culture conditions of Streptococcus thermophillus were: culture temperature 40℃, initial pH value 5.80, plain culture, culture time 12h.The optimum medium of these two lactic acid bacteria were obtained, the optimum MRS 1 medium of Lactobacillus bulgaricus: based on the modified MRS medium , added with 7.5% tomato juice ,12% mash liquor , 0.009mol/L CaCl2 and 2% whey; the optimum MRS 2 medium of Streptococcus thermophillus.: based on the modified MRS medium , added with 3% beer , 12% mash liquor , 6% tomato juice , 2% whey and 1% CaCO3. Neutralization experiments were carried with 20% NaaCO3 solution as neutralizing agent. After incubation , the viable counts of Lactobacillus bulgaricus and Streptococcus thermophillus were 7.5 × 109cfu/mL and 3.6 × 109cfu/mL, respectively.Fermenting liquor of these two lactic acid bacteria was centrifuged (4000rpm × 20min) to make cell suspension with multiple protector. Powdered starter was obtained by vacuum freeze drying. The viable counts of the starter were: Lactobacillus bulgaricus 2.1 × 1010cfu/g,. Streptococcus thermophillus 1.7 × 1010cfu/g.Powdered starters of Lactobacillus bulgaricus and Streptococcus thermophillus were added into carotene skim-milk with ratio of 1:1 and activated for 40 ~ 60 minutes at 42 ℃. Synthetic assessment method of fuzzy mathematics was used to evaluate the quality of the yoghurt prepared with the starter (inoculum size 0.18% ~ 0.37%), which proved that quality of the starter was excellent.