以费氏丙酸杆菌为研究对象,采用真空冷冻干燥法制备直投式酸奶发酵剂。通过单因素实验,以酸度和活菌数为测定指标,对脱脂奶粉、蔗糖、谷氨酸钠、明胶、甘油和山梨醇6种保护剂进行筛选。结果表明,脱脂奶粉、蔗糖、谷氨酸钠3种保护剂效果较好,确定为复合保护剂的基本成分。进而,以酸度为指标采用响应面法对复合保护剂进行优化,确定了最优的复合保护剂配方为:脱脂奶粉11.82%,蔗糖7.03%,谷氨酸钠2.98%。在最优条件下,直投式费氏丙酸杆菌发酵剂发酵酸奶的酸度达到69.2712+0.2425,与理论预测值71.0683接近。

The research focused on the preparation of Directed-Vat-Set( DVS) yoghurt starter cultures using Propionibacterium freudenreichii through Vacuum Freezing Drying technique and the optimization of its condition through single factor and response surface assays. The results showed that skimmed milk,sucrose and sodium glutamate were more effective than gelatin,glycerol,sorbitol through determination of acidity and viable bacteria count in single factor assay. The optimal condition was as follows: skimmed milk 11. 82%,sucrose 7. 03%,sodium glutamate 2. 98%. At the best condition,yoghurt fermented by this DVS had a acidity of 69 ± 0. 2425,which was approaching predicted value of 71. 0683.