Lactic Acid Bacteria High Density Culture And Solid Development Of Viable Yoghurt

When the Chinese are spending more than before,milk and dairy products have gradually become a necessity for people to supplement their nutrition.As one of the most traditional fermented dairy products,yoghurt is favored by consumers because of its rich nutritional value and good health care functions.In recent years,with the advent of the concept of active lactic acid bacteria,active lactic acid bacteria-based beverages have become popular in the market,and active lactic acid bacteria-based solid products are still temporarily in the market.Therefore,in this study,the main purpose of preparing active lactic acid bacteria solid products,the screening of strains,high density culture of bacteria and research and development of active lactic acid bacteria solid product in three parts.The main findings are as follows:1.To isolate and purify the four mixed species of Mycobacterium tuberculosis preserved in the animal husbandry laboratory to obtain Nos.1,2,3,4 and 1,2,3,and 4 bacilli.The survival rate and stability of viable bacteria in gastric juice and intestinal fluid during the reaction of simulated intestinal fluid with a pH of 8 were simulated by a simulated gastrointestinal fluid method.The No.2 and No.2 cocci in simulated gastric juice were most suitable for the gastric juice environment;No.4 and No.1 cocci in simulated intestinal fluid were most suitable for the bile salt environment.At the pH value of 3,the No.3 and No.3 cocci in the simulated gastric juice were most suitable for the gastric juice environment;the No.3 and No.1 cocci in the simulated intestinal fluid were most suitable for the bile salt environment.At pH=2,No.3 and No.2 cocci in simulated gastric juice were most suitable for the gastric juice environment;No.3 and No.4 cocci in simulated intestinal fluid were most suitable for the bile salt environment.The growth performance of each strain was determined by single-strain fermentation,and it was found that No.2 and No.3 bacilli had a faster acid production rate and a moderate viscosity;No.1 and No.2 cocci had a fast acid production rate and a large viscosity.The sensory scores of fermented milk of each single strain were obtained and it was concluded that the total scores of the sensory evaluations of No.1 and No.3 bacteria and No.2 and No.3 cocci were the highest.Comprehensive analysis and evaluation,selection of No.3 Lactobacillus bulgaricus and No.2 Streptococcus thermophilus was mixed in a 1:1 ratio as a fermentation bacterium to prepare high-density active yoghurt.2.Single factor test,orthogonal test,climbing test and response surface method to obtain 3%inoculum size,culture temperature of 42 ?,2h 3min fermentation,add 15%sodium carbonate buffer salt to adjust the pH to 6.63,while adding fermented milk 1.07 times the volume of nutrient solution(whey:tomato juice:carrot juice:milk = 4:6:6:5),continue to culture 1h 53min after the stop fermentation,4 ? cold cooked.The total number of lactic acid bacteria colonies can reach 5.86×1010 cfu/mL.3.High-density yogurt sensory score slightly higher than non-high-density yogurt.With the prolongation of storage time,the stability of the trends of physical and chemical indicators of high-density yogurt is lower than that of non-high-density yogurt.The total number of colonies,bacilli,and bacteria were higher than non-high-density yoghurts 2.04%,1.04%,and 1.67%.(The"high-density yogurt" mentioned in this article refers specifically to yogurt prepared by using high-density fermentation agents prepared by high-density culture of common yoghurt starters."Non-high-density yogurt" refers specifically to yogurt prepared using ordinary starter cultures..)4.The survival rate of viable bacterium after freeze drying,blast drying,microwave drying and spray drying was 72.27%,53.87%,32.6%and 38.54%,respectively.Solid Active Yogurt Sensory Score Fractional Spray Drying>Freeze Drying>Microwave Drying>Air Drying.Orthogonal experimental design to obtain high-density yogurt best freeze-dried protective agent formula is 0.6%trehalose + 0.6%glycerol + 2%skim milk + 0.6%whey.The optimized protective agent can make the survival rate of high-density yoghurt live bacteria reach 83.29%,and the freeze-drying efficiency is 3.32%higher than that before optimization.