Study On Processing Key Technique And Quality Of Low Temperature Long Term Fermentation Yogurt

Basing on traditional processing theory of yogurt, combining the development of yogurt's process, low temperature and long term fermentation yogurt was studied in thermal treatment, optimum process parameter and the variation of physical and chemical character, flavor, plate count of the lactobacillus. The conclusion of studying on the optimum process parameters and compare of quality of low temperature and long term formation yogurt could provide experimental and academic gist for industrialization.The result indicated the optimum thermal treatment of restituted milk was 95 ℃ heating 5 minutes.The optimum process parameters of low temperature and long term fermentation yogurt were obtained by L9 (34) orthogonal design and analysis of variance on the results. The results indicated that the optimal culture parameters of low-temperature and long-term fermentation yogurt was that the proportion of S1:Lb was 4:1, the yogurt starter was added at a level of 3% by volume, sucrose was added at a level of 8%, and incubated at 34℃ for 10 hours.Sensory score, pH value, acidity, pure protein, free amino acid, fat, acetaldehyde, diacetyl contents and plate counts of lactobacillus of two yogurts (low temperature and long term fermentation yogurt , high temperature and short term fermentation yogurt) were checked and measured after fermentation, storing at 4℃ for 24h and storing at 4℃ for 4 days. The result indicated:Sensory evaluation showed that low temperature and long term fermentation yogurt had both good coagulation and smooth texture withdesirable flavor. Physical-chemical analysis showed that acidity of the low temperature and long term fermentation yogurt was 72. 33°T, acetaldehyde was 14. 46 mg/kg, diacetyl was 4. 72 mg/kg. The content of acetaldehyde and diacetyl of low temperature and long term fermentation yogurt were always in the best bound in the whole process. Low temperature and Long term fermentation yogurt had feebleness ability of post-acidification. The free amino acid of low temperature and long term fermentation yogurt increased obviously. Low temperature and long term fermentation yogurt had abundant alive lactobacillus. The plate count of lactobacillus could reach 8.9×108cfu/ml. So the Low temperature and long term fermentation yogurt had better quality.