| With the rapid development of the fermented dairy industry, study on the probiotic starters is of great importance to promote the industrialized process of lactic acid bacterial starters. This paper is aimed at selecting the cheap enrichment medium , freeze-drying protectants and research on the high density cultivation, cell concentration, freeze-drying and spray-drying technology to produce probiotic starters with high viability. We also examined the fermentation activity of the starter and flavors of the yogurt using GC-MS. The results indicated:⑴.Through the comparison of five different mediums, enzymatic hydrolyzing whey adding 1% beef extract is better to produce probiotic starters. The conditions of enzymatic hydrolysis were studied by single factor experiment. It was concluded that the optimal condition of enzymatic hydrolysis were 10% whey, enzymatic time 3h, E/S 0.16, enzymatic temperature 50℃.⑵.Results of high density cultivation showed: inoculum volume was 8%, incubation temperature was 37℃, oscillation frequency was 160r/min. After 12h cultivation, we started to feed till harvest and the viable count was above 1010 cfu/mL at the end.⑶.Results of concentration conditions showed: freeze-drying survival rate was the highest at 4000r?min for 10min. Concentration temperature had no significant influences on the freeze-drying survival rate.⑷. The optimal composition of freeze-drying protectants was determined by orthogonal test. Results indicated that the ingredients of freeze-drying protectants are 4%RSM, 12%sucrose, 1.5%sodium glutamate and 1%fucose. The final viable count of freeze-drying starter was above 1011 cfu/g.⑸.In order to produce probiotic starter with high viability, we combined microcapsule and spray-drying technology together. We choosed RSM and gum acacia as the best wall material in three different materials. The inlet air temperature and the wall material concentration were also determined. Results showed: we could get the highest viable count when the the wall material concentration was 20% and the inlet air temperature was 140℃. The final viable count of spray-drying starter was above 1×108 cfu/g.⑹.Through the study on antioxidation of L. acidophilus, we use the D- galactose induced rats to carry on the experiment. Results showed that compared with model group, MDA content in the liver of the rat decreased rapidly; GSH-Px increased rapidly both in liver and serum; T-AOC increased in serum; L. acidophilus preparation could increased HDL levels rapidly in the liver.⑺.By culture starter qualify test, we could find that: the viable count of freeze-drying starter during storage period remained stable, however the viable count of spray-drying starter decreased rapidly in three months'storage; In the first 4 hours, freeze-drying starter don't show rapid acid decrease as the liquid starter in the mink. But in the next few hours it showed rapid acid decrease. Spray-drying starter is a little bit slow than freeze-drying starter on the acid production.⑻. We could examine 17 kinds of flavors in the yogurt fermented by L. acidophilus. It conclude 7 kinds of esters, 1 kind of ethanol, 4 kinds of acids, 1 kind of aldehydes, 4 kinds of ketones. |
