Optimization of Fermentation Parameters for Production of DVS Yogurt Starter Cultures

The interactions(including the symbiosis and antagonism) and their capabilities to produce lactic acid, viscosity,and acetaldehyde. between Streptococcus thermophilus strains and Lactobacillus delbrueckii subsp. bulgaricus strains were studied. It was seen that 3 paired strains were more suitable for the production of yogurt. For strains LB2-ST1, the optimun media were 1.0% of tomato extract, 1.0% of lactose, 0.5% of yeast extract and 1.0% of peptone. If they were cultivated at 42℃ for 6h. The cell population was up to 1.64×109CFU/ml. The optimal cryoprotectants to improve the viability of strains LB2-ST1 were investigated .A combination consisting of trehalose (0.5%), glycerin (0.3%), glutamate-Na (5%) and Sorbitan mono-oleate (0.3%) could produce a very positive effect on promoting the viability of the paired strains LB2-ST1.Their viable cells after freeze- drying were 3.62×1011CFU/g. The optimal parameters for the production of yogurt starters were: temperature 42.2℃, pH6.4, rotating speed 86.7r/min, inoculation 4%, feeding 1.0%, fermentation 6h and freeze-drying -40℃ for 15h. The cells of the production were1011CFU/g。