Development Of Direct Vat Set Cultures For Soy Yoghurt

The continuous increasing in population and inadequate supply of protein has inadvertently increased the occurrence of malnutrition in developing countries. However, in order to meet the demands in developing countries for protein, where animal protein is also grossly inadequate and relatively expensive, research effort is geared towards finding alternative sources of protein from legume seeds. And soymilk is recognized as being nutritionally helpful, soy yoghurt (a product from soymilk) has some advantages in terms of nutrition and health, since it contains no cholesterol or lactose and only small quantities of saturated fatty acids; in addition to low cost.The thesis conduct a systematic research on production of soymilk, screening of excellent LAB strains, high cell density cultivation of LAB strains, freeze-drying, the quality evaluation of freeze-drying production. The experiment testifies as following:It is effective for eliminating the beany flavor when heated to90℃, and the best soymilk and milk ratio tured to be3:2.In this experiment, the soymilk-milk was used as substrate, and the fermentation characteristics of56lactic acid bacteria strains were studied. Five strains including Lactobacillus bulgaricus358, Lactobacillus bulgaricus117, Streptococcus thermophilus240, Streptococcus thermophilus242, Bifidobacterium bifidum031with excellent ability of acid production were selected. The optimum combination were Lactobacillus bulgaricus358, Streptococcus thermophilus242and Bifidobacterium bifidum031, and the optimal proportion of strains was358:242:031=3:5:2, which was determined by simplex centroid design.The single factor experiment of15liter fermentation indicated that the optimal fermentation conditions of Lactobacillus bulgaricus358and Streptococcus thermophilus240were as follows: fermentation temperature was37℃, the rates of inoculation were2%, and the fermentation pH was controlled at6.0; While the optimal fermentation conditions of Bifidobacterium bifidum031were: fermentation temperature was37℃, the rates of inoculation were2.5%, and the fermentation pH was controlled at5.8. The high cell density culture was carried out, and cell number can reach to8.4×108cfu/mL,4.7×109cfu/mL,3.2×109cfu/mL accordingly.Compared to the change of Electric Resistance of Eutectic, the Eutectic temperature and melting temperature of freeze-dry specimen was measured as follows:Lactobacillus bulgaricus358at-38.0±0.4℃, Streptococcus thermophilus242at-37.1±0.3℃, while Bifidobacterium bifidum031at-37.3±0.5℃. Then according to this parameter, new freeze-drying technology was formulated, the whole freeze-drying period took only37.5hours, which was more effective than the traditional freeze-drying technologies.The process under the conditions of production of freeze-drying power was evaluated, and Sensory indicators, physical, chemical indicators and microbial indicators are in line with the requirements of Enterprise Standard Q/AATZ0001S-2012from BioGrowing.The cell number of freeze-drying power of Lactobacillus bulgaricus358, Streptococcus thermophilus240and Bifidobacterium bifidum031can reach to3.3×1010cfu/g,5.4×1011cfu/g,3.8×1011cfu/g accordingly. The Production could store for1year at the temperature of-18℃;Soy yoghurt fermented by new starter culture GF478uniform milk yellow, delicate organization status, sensory evaluation for good.