The Development Of ATPase Defective Culture Starter Of Lactobacillus Bulgaricus

In yoghurt production, yoghurt freeze-dried starter culture was widely used. Lactobacilus delbrueckii subsp. bulgaricus produces lactic acid during the storage, and caused the post-acidification of yoghurt. To inhibit the post-acidification, low H+ -ATPase acticity strain was screened by MRS broth contained 100μg/mL neomycin. Low L 15-4 was High density fermented ,centrifuged ,freezed-driedComparisons of the yoghurt were made, which were fermented with the screened strain and the parental strain. Yoghurt made with strains isolated from retail saled yoghurt was as the control group.Skim milk were inoculated with 5.0×106CFU/ml of Lactobacilus delbrueckii subsp. Bulgaricus and the mixed strain of Lactobacilus delbrueckii subsp. Bulgaricus and Streptococcus thermophilus at 42°C, and stored at 4 and 20°C for several days.The pH and tiration acidity of fermented milk was checked at .The post-acidification of fermented milk using strain L15-4 was weaker than the fermented milk using parental strain L15 and the strain LW-1.With the development of yoghurt in the world, the post-acidification problem becomes a main factor which affecting the quality of yoghurt during the process of yoghurt sales. And this problem restricts yoghurt consumption seriously. The post-acidification of yoghurt was caused by the continued metabolism of lactose by Lactobacillus bulgaricus during the storage of yoghurt. In this paper, we have conducted in-depth studies of post-acidification strains in yoghurt, including: screening of the weak post-acidification strains; optimizing the culture of lactobacillus and vacuum freeze-drying process conditions; and so on.In order to find the optimal cultivation conditions for L15-4, a single-factor test with MRS medium was designed, and filtered out the optimum temperature was 37℃, the pH was 5.8.Use MRS medium as the basal medium, through the L9(33) orthogonal test, we found the best combination of medium was No.5: skim milk 3%, tomato juice 5%, yeast extract 0.5%, the highest bacterial density 1.44×109 CFU/mL. The optimal combination of filter medium: skim milk 3%, tomato juice 5.0%, yeast extract 1.0%.After the high-density fermentation, the number of Lactobacillus bulgaricus was maximum. We have determined the centrifugation conditions by studying the centrifugal force, centrifugation time of cells. And the most suitable centrifugation condition is: 6000r/min, 20min, and the experience rate of 87.30%. By four factors, three-level orthogonal test, the freeze-dried cryoprotectant was screened, the best protective agent formula was: skim milk 8%, trehalose 2%, glycerol 2%,L-glutamic acid 2%.We use freeze-dried powder to ferment yoghurt, mixed with coccus to ferment yoghurt separately. 4℃, 20℃21d, detected the stability of the weak post-acidification after freeze dried and found that the weak post-acidification was stable after or before freeze dried.Conclusios is that The post-acidification of fermented milk using Lactobacilus delbrueckii subsp. Bulgaricus neomycin was weak, and it is acceptable to use selected Bulgaricus ferment milk.