Study On High Density Culture And Freeze Drying Protection Of Lactobacillus Bulgaricus NQ2508

Lactobacillus bulgaricus is an essential strain in yogurt starter culture and probiotic preparations.In the process of industrial production,production efficiency and cost significantly affect the application and promotion of products.The research object of this paper is Lactobacillus bulgaricus NQ2508 from a pharmaceutical company in Inner Mongolia,which is used for the production of microecological preparation products of the company.In the current production process,the number of viable bacteria in the powder is significantly reduced because the concentration of the culture is not high,as well as the loss in the freeze-drying process.This aspect affected the probiotic function of the strain and increased the cost of industrial production.Based on the current production situation,this study achieved the high-density culture of Lactobacillus bulgaricus NQ2508 through the optimization of medium composition and fermentation feeding strategy,further through the study of NQ2508 freeze-drying protective agent,improve the survival rate of NQ2508 freeze-drying.The reaserch above is aimed to improve the production efficiency.and the results of these study provide a reference for enhancing the industrial production level of Lactobacillus bulgaricus.The main findings include the following:1)At the shaking flask level,the breeding medium of Lactobacillus bulgaricus NQ2508was improved regarding the MRS Medium.Moreover,the proliferation effects of different carbon and nitrogen sources,carbon and nitrogen ratio,and nutrient enhancing-substances on the proliferation of Lactobacillus bulgaricus NQ2508 were investigated,and the proliferation medium of Lactobacillus bulgaricus NQ2508 was determined.The results showed that the carbon and nitrogen sources of the breeding medium were glucose 12.0 g·L^-1,casein peptone4.0 g·L^-1,and beef powder 8.0 g·L^-1.The number of viable bacteria cultured by proliferation medium was 1.54×10⁹ CFU·mL^-1.2)The effects of pH and substrate supply on the growth of Lactobacillus bulgaricus NQ2508 were investigated following different fermentation strategies at the level of a 3 L fermenter.First,Lactobacillus bulgaricus NQ2508 was cultured in batches at constant pH and interval pH,and the viable bacteria numbers were 1.66×10⁹ CFU·mL^-1 and 1.82×10⁹ CFU·mL^-1,respectively.Subsequently,the control of glucose concentration and pH during the feeding culture of Lactobacillus bulgaricus NQ2508 was investigated,as well as the effect of the feeding medium composition on its growth.Different fed-batches of Lactobacillus bulgaricus NQ2508 were cultured,and the maximum viable bacteria number reached 2.85×10⁹ CFU·mL^-1.Finally,the analysis of the relationship between glucose consumption rate and pH decrease rate enabled to establish the feedback feeding strategy based on pH decrease rate.The average number of viable bacteria in the Lactobacillus bulgaricus NQ2508 culture was 3.60×10⁹CFU·mL^-1.3)The effect of different protective agent compositions on the lyophilized survival rate of Lactobacillus bulgaricus NQ2508 was studied.Moreover,the effects of skim milk,carbohydrate,antioxidant,sodium glutamate,betaine,and xanthan gum on the lyophilization of strain NQ2508 were investigated.The results showed that the optimal formula was 20%skim milk,20%lactose,2.6%ascorbic acid,and 2.6%sodium glutamate.Moreover,the optimal ratio of bacterial mud to protective agent was 1:1,and the optimal pH of bacterial suspension before lyophilization was 4.5.The high-density culture of Lactobacillus bulgaricus NQ2508 was achieved using a feedback feeding strategy based on the pH decrease rate established in this study.After culturing at the level of 5 L fermentor,the number of viable bacteria reached 4.87×10⁹ CFU·mL^-1,which was 159.0%higher than that of the control batch culture.The yield of bacteria and the production efficiency of each batch increased by 35.6%and 288.1%.The confirmed formulation of the protective agent increased the lyophilized survival rate of Lactobacillus bulgaricus NQ2508 to an average of 40.3%.The feedback feeding strategy and proposed lyophilized protective agent improved the production efficiency of Lactobacillus bulgaricus NQ2508 and its industrial application value.