Study Of Direct-Vat-Set Probiotics Starter Cultures Based On Skim Goat's Milk

In order to adapt the social development trend,meet the requirements of people's diversified drink choices,and improve the inadequate development of goat's milk resources in our country,the milk beverage of probiotic straight type yeast is developed,which is of great significance to promote the development of goat's milk industry.On the basis of previous experiments,the research discussed comparative of different probiotic fermentation characteristics and selected the target bacteria based on skim milk's fermented substrate,the optimization of selection for oligosaccharides multiplication factors,the choice of freeze-dried powder,the comparison of preservation conditions for freeze-dried bacteria powder,and the verification of starter's performance,etc.The research provide technical reference for industrial preparation of freeze-dried bacteria powder in high dynamic milk beverage.The main research results are as follows:1)Through contrast in the fermentation performanc of Lactobacillus Casei,Lactobacillus Acidophilus,lactobacillus plantarum,Lactobacillus Paracasei and Bifidobacterium longum in skim milk,according to the regulating mechanism in the symbiosis of probiotics,and on the basis of a single strain fermentation experiment,the number of viable probiotics count,acidity,viscosity,and pH were superior to other combinations when the cheese of Lactobacillus Casei and bifidobacterium longum were used as compound probiotics.And the best fermentation performance were determined with a ratio of 3:1 for the probiotic compound.On the basis of single factor experiment and through the response surface method,the optimized fermentation conditions were determined:the fermentation temperature was 37?,the inoculation volume was 4%,the fermentation time was 55 h,and the maximum number of viable probiotics count was9.63×10⁸ CFU/mL.2)By comparing the effects of different oligosaccharides on the proliferation of mixed probiotics,it was found that fructo-oligosaccharides,galacto-oligosaccharides,xylo-oligosaccharides and inulin had significant effects on the proliferation of probiotics.The effects of different oligosaccharide contents on the number of viable probiotics,fermentation acidity,pH and viscosity were studied.The addition level with good effect on probiotics proliferation was selected,and the technological parameters of oligosaccharide addition were further optimized through orthogonal experiment.The final determination was as follows:the addition amount of fructo-oligosaccharides was 0.60%,the addition amount of galacto-oligosaccharides was 0.90%,the addition amount of xylo-oligosaccharides was 0.90%,and the addition amount of inulin was 0.60%.Under these conditions,the maximum number of viable probiotics count was 9.33×10¹00 CFU/mL.3)On the basis of single factor test,four freeze-dried protectants with better protective effect on bacteria were selected,namely skim goat's milk,glycerin,trehalose and ascorbic acid,and the process conditions of these protectants were optimized by response surface method.The results showed that the best formula of freeze-drying protectant was:10%skim goat's milk,4%glycerin,4%trehalose,and 0.07%ascorbic acid.During the same time,the OD value was 1.677,the maximum number of viable probiotics count was 7.72×10¹⁰CFU/mL after rehydration of the powder,and the freeze-drying survival rate of the bacteria was 83.20%.Through contrasting the probiotic's survival rates when the storage conditions of freeze-dried powder were 4?and-18?,-18?was more advantageous for the fungus preservation of powder,and could maintain high survival rate of 82.23%in storage after 60d.Through the verification of the fermentation performance of freeze-dried bacterial powder,the trend of the acidity of liquid bacterial suspension and freeze-dried bacterial powder in the fermentation process was basically consistent,indicating that the fermentation performance of freeze-dried bacterial powder was relatively stable.