Study On Fermented Technology Of Probiotic Yogurt Based On Viable Probiotics Count

The viable probiotic count was the key factor to functionality of probiotic milk beverage. But when determining the total viable count by GB4789.35-2010, the accuracy of determination results was not high because of Lactic acid bacteria cells scattered unevenly. To optimize the probiotic measuring method of total viable count,increase and delay the number of viable bacteria, The existing measuring method of total viable count was improved first. Then blend probiotics with high acids and high number of viable bacteria were selected and added amount of compound oligosaccharides were optimized in the Probiotic milk beverage.The main research contents were as follows:(1) EDTA was used as a chelating agent. an improved method for determination of total viable count in fermented milk was provided, through the optimization of EDTA addition amount and pH value. The results showed that the optimal condition was:EDTA addition amount was in the range of2%-6%, the pH value was in the range of6.88.8. In the optimal ranges, fermented milk diluent could clarify in short time, the death of bacteria cells were prevented caused by high osmotic pressure and high alkaline environment,the accuracy of determination results were ensured. Measurement results were close to the results using GB4789.352010, and the measurement precision was higher than the precision of the determination results using GB4789.352010.(2) Lactobacillus casei、Lactobacillus acidophilus、Bifidobacterium、Streptococcus thermophilus and Lactobacillus bulgaricus were studied. Probiotics with high acids and hign number of viable bacteria were selected by single strain fermentation and compound microbial fermentation. In the condition of5%inoculation volume,1:1inoculation proportion,37℃fermentation temperature,2.5%glucose content,12%milk solid content, the optimal portfolio of fermentation was the combination of Lactobacillus casei and Bifidobacterium, the maximum acid production was328T°, the maximum number of viable probiotics was2.3X1011mL-1. Compared with other bacteria combination, a logarithmic level was improved and the number of viable probiotics declines slowly during the storage.(3) On the basis of (2), fructooligosaccharide, isomaltooligosaccharide, soybean oligosaccharide and xylooligosaccharide were studied on the viable count of probiotic milk beverage in storage period. The viable count and pH were used to assess the production quality. Orthogonal test was carried out on the single factor experiment of determining the optimum addition amount of various factors. The result of range analysis and variance analysis were conducted. Results showed that the optimal formulation was: fructooligosaccharide content was2.0%, isomaltooligosaccharide content was1.56%, soybean oligosaccharide content was1.71%, xylooligosaccharide content was0.32%. Verification test demonstrated the number of viable probiotics count was2.7X1010cfu/mL and the pH value was3.83, when stored under4℃after21d. The number of viable count of no adding oligosaccharide probiotic milk beverage was1.4×109cfu/mL and the pH value was3.87. Compound oligosaccharides raised a logarithmic in maintaining the number of viable probiotics count, but it was no significant effect on post-acidification during storage period.