Study On High Cell Density Culture And Vacuum Freeze-drying Of Lactobacillus Delbrueckii Subsp. Bulgaricus IMAU80319

Lactobacillus delbrueckii subsp. bulgaricus is an important component for yogurt starter culture applied in dairy industry, however, viable counts and viability of domestic starter culture are relative low. It is significative to screen Lactobacillus delbrueckii subsp. bulgaricus with superior fermentation characteristics and study the technology of high cell density cultivation and vacuum freeze-drying to improve the quality of starter culture and obtain strains with independent intellectual property rights and lower the cost of dairy company.By detecting the fermentation properties of the strains and characterization of their fermented yogurts,8 strains were screened from 171 Lactobacillus delbrueckii subsp. bulgaricus by comparing with Lactobacillus delbrueckii subsp. bulgaricus ND02, which was an excellent strain in fermentation. Lactobacillus delbrueckii subsp. bulgaricus ATCC11842 was used as control to detect the resistance of the screened strains to the virulent phage. The results showed that IMAU80319 and MAU20422 were resistance to virulent phage phiLdb.MRS was used as basic medium, all ingredients resource and concentration were optimized to study the optimum medium for Lactobacillus delbrueckii subsp. bulgaricus IMAU80319, and amounts of each component were designed by Box-Behnken method. The optimal medium of IMAU80319 were as follows:glucose of 1.67%, carbon sources B of 1.67%, lactose of 1.12%, nitrogen sources B of 1.69%, nitrogen sources C of 1.69%, beef extract of 1.13%, KH2PO4 of 1.33%, NaOH of 0.23%, MnSO4 of 0.05%, CaCl2 of 0.31%. Optimal static cultivation was obtained by single factor test and the results showed that the strain can grow well in 41℃ with initial pH value of 6.6 by using 6% inoculum.Based on the optimized medium and static cultivated conditions, technology of high cell density fermentation was studied. The best fermentation conditions:constant pH value of 5.0, neutralizer of 25% ammonia and revolution speed of 200rpm.The addition proportion of protective agents and the freeze-drying process of Lactobacillus delbrueckii subsp. bulgaricus IMAU80319 were studied. The sample was pre-freezed in -40℃ for 8h with protective agents of sugar, polyols and salts which were added as proportion of 1:6.Lactobacillus delbrueckii subsp. bulgaricus IMAU80319, the cultivation time was only 6 to 6.5h which was shorter than before for 3h. And viable counts could reach 57×108CFU/mL. The viable counts of freeze-dried powder were 11×1010CFU/g, and the survival of freeze-dried processing could reach 83.9%, which was enhanced for 30% more than the original technology.