Study On The Kefir Soybean Yogurt Direct-Vat-Set Cultures (DVS)

Kefir grains is a starter cultures of kefir dairy products. The unique microbes symbiotic system of kefir grains makes its products are better than the ordinary yogurt in terms of physiological function. We found kefir grains was suitable starter of soybean yogurt based on the results of long-term preliminary experiment researches. The soybean milk partly replace the milk to make similar traditional kefir milk, not only can meet the national diet and the dietary requirements of modern people, but also can reduce the production costs. But kefir grains could not be synthetic, it's a kind of natural and synthetic yoghurt starter cultures. The slower growing expansion speed and the unstable proportion of microbial limit the industrialized production of kefir dairy products. Therefore, a kefir direct-vat-set cultures(DVS), which owns higher live bacteria content, strong fermentation activity and stable quality, has important application prospect. This research focused on the mixed high density fermentation of kefir grains, the choice of harvest fungus age, the screening and optimization of cryoprotectant, the metagenomics sequencing of starter cultures, the formula optimization of soybean yogurt, the pilot test of kefir DVS and the market research of soybean yogurt. The main results were as follows:? The living bacterium content of lactic acid bacteria in the kefir mother liquor occupied obvious advantage, was(1.60±0.19) ×108cfu/m L, 42% of the total number of main living bacterium. Followed by yeast, was(1.16±0.04) ×108cfu/m L, 30% of the total number of main living bacterium. The acetic acid bacteria at the least, was(1.07±0.04) ×108cfu/m L, 28% of the total number of main living bacterium. The Lactococcus of the mixed soymilk yogurt and pure soybean milk yogurt which fermented by kefir mother liquor were both above 85%. And the Lactobacillus of the mixed soymilk yogurt was 6.34±0.02%, which was about 2.5 times of the pure milk yogurt, 4.5 times of pure soybean milk yogurt.? The optimal formula to ferment soybean yogurt with kefir DVS: The ratio of soybean milk and milk was 1:1, content of sugar was 8% and the inoculum size was 50mg/L. And the soybean yogurt had good sensory flavor, no precipitation of whey, nice curd, exquisite texture, sweet and sour moderate.? The kefir DVS showed high activity and good quality of soybean yogurt when the harvest fungus age was 32 h. At this point, the number of living bacterium were highest, were 4.43×1010cfu/g, and the living bacterium number of lactic acid bacteria were 2.18 × 1010cfu/g. The soybean yogurt had good sensory flavor, p H was 4.31, acidity was 77.80 °T, and retention ability was 70.58%.? The optimum cryoprotectant of DVS: The skimmed milk 23.99g/100 m L, the sucrose 8.00g/100 m L, the lactose 8.39g/100 m L. The actual values of Lactic acid bacteria, yeast and acetic acid bacteria were 95.12%, 92.37% and 90.65% respectively.? The living bacterium content of lactic acid bacteria in the kefir DVS occupied obvious advantage, was(2.43±0.08) ×1010cfu/g, 62% of the total number of main living bacterium. Followed by yeast, was(7.60±0.60) ×109cfu/g, 19% of the total number of main living bacterium. The acetic acid bacteria at the least, was(7.30±0.50) ×109cfu/g, 19% of the total number of main living bacterium. The living bacterium content of the three main bacteria changed obviously compared with the kefir mother liquor after mixed high density fermentation. The number of lactic acid bacteria increased significantly, while the number of yeast and acetic acid bacteria were significantly reduced. The Lactococcus of the pure milk yogurt and the mixed soymilk yogurt which fermented by kefir DVS were both above 97.00%, and were about 1.15 times of the pure soybean milk yogurt. The Lactococcus of the pure milk yogurt which fermented by kefir DVS was 97.41±0.01%, was about 1.16 times of the pure milk yogurt which fermented by kefir mother liquor. The Bacillus of the pure soybean milk yogurt which fermented by kefir DVS was 12.06±0.04%, was about 13.86 times of the pure soybean milk yogurt which fermented by kefir mother liquor. The Acetobacter of the pure milk yogurt which fermented by kefir DVS was 1.51±0.01%, was about 1/26 of the pure milk yogurt which fermented by kefir mother liquor. The Lactobacillus of the mixed soymilk yogurt which fermented by kefir DVS was 0.61±0.00%, was about 1/10 of the mixed soymilk yogurt which fermented by kefir mother liquor.? The kefir soybean yogurt showed good weak after acidification characteristics at 4?storage conditions: During the 12 weeks of storage, the p H of kefir soybean yogurt was only increased 0.04. The acidity reduced after increasing, but only changed 2.50°T.? Our kefir soybean yogurt were superior to “Weidou” soybean yogurt on the sensory evaluation, and received good feedback from the survey respondents in the market research. But we also need to increase the propaganda work of kefir and soybean isoflavones health efficacy on the basis of good flavor, if we want to broaden kefir soybean yogurt market.