Study Of Chinese Yam Yogurt Fermentation By Novel Probiotic Lactic Acid Bacteria

Yam is a traditional agricultural product with nutritional and medicinal health value. Mucopolysaccharide, diosgenin, allantoin and other biologically active ingredients contained in fresh yam give the spleen and stomach, lowering blood sugar, anti-aging, anti-tumor and other health effects, so that yam has a very high value of processing and utilization. While protein content of yam is not high, but the quality of protein is high and all kinds of amino acid ratio is reasonable. Its biological utilization rate in the human body is higher than cereal. If you add some high protein-rich milk while eating yams, can meet the body’s basic nutritional requirements. Probiotic lactic acid bacteria can maintain a symbiotic relationship with the human body, colonization in human intestinal mucosa surface, and form a biochemical barrier to play a beneficial role in promoting human health. With the deepening of Medicinal and Edible products’ functional research and probiotic lactic acid bacteria benefited to human body health care have been revealed, probiotic Lactobacillus research and development of traditional Chinese medicine health food become the focus of attention in the field of food science.Since the21st century, people’s living standards and health care consciousness unceasing enhancement, accelerating the development of food, improving food structure, nutrition levels and enhancing people’s physical health have been the urgent need to improve the quality of the national overall, therefore actively developing the dairy with nutrition and health functions is beneficial measures to achieve this goal. The research is based on the cow’s milk as the main raw material, yam as a nutritional supplement material, and using of probiotic lactic acid fermentation to make a kind of new functional yogurt integrating multiple nutritional health care efficacy.The present study used11strains of probiotic lactic acid bacteria which were isolated from natural fermented food, probiotics and health products were studied as test strains to ferment chinese yam milk. Through the analysis of pH value, viable count, physicochemical characteristics and sensory evaluation, we determined2strains of probiotic lactic acid bacteria with high reproductive capacity, high fermentation vigor as well as good flavor which were suitable to ferment chinese yam yogurt, respectively Lactobacillus casei05-20and Lactobacillus plantarum FS-4. Due to weak acid production of probiotic lactic acid bacteria in pure breed fermentation, they will be supplemented by Streptococcus thermophilus and Lactobacillus bulgaricus to mixed fermentation.The effect of water ratio of yam solution, yam solution concentration and sugar concentration in yam milk on fermentation curd time, pH, titratable acidity, syneresis sensitivity, the number of viable cells and sensory characteristics were studied. On the basis of above, using orthogonal experiment to optimize the level of yam milk fermentation medium, the result were that water ratio of yam solution was1:3, the yam solution concentration was20%, the sugar concentration was6%.This paper studied the effect of the inoculation amount, the proportion of mixed bacterial and fermentation temperature in the fermentation medium on fermentation curd time, pH, titratable acidity, syneresis sensitivity, number of viable cells and sensory characteristics. On the basis of above, using orthogonal experiment to optimize the fermentation conditions of yam yogurt, the result were that the inoculation amount was4%(V/V), the proportion of mixed bacteria was05-20:Fs-4: St-LDY:Lb-DR=1:1:2:1, fermentation temperature was37℃In this experiment, using "national food safety standards-fermented milk"(issued by the Ministry of Health of the People’s Republic of China) as a specific reference to preliminary analyze and evaluate the sensory indicators, physical and chemical indicators, health indicators, number of viable lactic acid bacteria cells of yam yogurt products, the results showed that:yam yogurt’s color uniform, milky white, with rich fermented aroma, sweet dianty, no whey separation and stratification; fat content of2.72g/100g, protein content of3.27g/100g, acidity77.37°T; arsenic, lead, aflatoxin M1, coliforms, Staphylococcus aureus, Salmonella, yeast and mold were not detected in the yam yogurt products; viable lactic acid bacteria number was1.82×109cfu/mL. The yam yogurt fermented products fully comply with our quality standards, so various testing indexes can be judged to be qualified. The shelf life of yam yogurt was24d at4℃.This study combines the yam deep-processing and dairy industry development to ease yam resources surplus and milk relatively insufficient in our country at present, to further enrich the variety of dairy products, enhance nutrition and health care functions of dairy products, improve the hardship situation of "poor export and domestic sales are not prosperous" yam and open up new avenues of yam resource utilization. This study has a certain practical significance for enhancing the added value of the yam processing and promoting urban and rural economic development, but also provides a scientific basis for the industrial production of Lactobacillus casei and Lactobacillus plantarum mixed fermentation yam yogurt products and application.