Study On The Application Of Lactobacillus Helveticus AJT In Yoghurt

In China,the production and consumption of dairy products,especially all kinds of yogurt,are developing rapidly with the improvement of the quality of life,whilethe shortageof yogurt shelf life restricts the development of dairy industry.Most yoghurt manufacturers in Chinastill cannot guarantee the cold chain logistics,which links to the quality control of yoghurt.In order to improve the quality of yogurt,avoid increasing the transportation cost,the development of long shelf yogurt is worthy of being studied.In this experiment.L.helveticusAJT,which with broad-spectrum antibacterial activity,and S.thermophilus ST962 were selected as starter culture to study the fermentation characteristics of strain AJT in skim milk and the optimum fermentation conditions of this two mixed strains.The shelf life of traditional yoghurt made from L.bulgaricus LB 1823 and S.thermophilus ST962 was selected as the contrast.The main results were as follow:1.When strain AJT was inoculated into skim milk medium(inoculum amount 2%v/v),the curd time was about 12 h,the number of viable bacteria reached 1.6×109 CFU/mL,the pH value was 4.08,titratable acidity was 84 °T;when strain ST962 was inoculated into skim milk medium inoculum amount 2%(v/v),the curd time was about 6 h,the number of viable bacteria reached 1.3×109 CFU/mL,the pH value was3.42,titratable acidity was 61.68 °T.2.The optimal fermentation technology of yoghurt was obtained:the strain ratio of AJT and S?962 was 1:3.inoculum quantity was 40%(v/v).fermentation temperature was 42?,sucrose content was 6%(g/v).3.yogurt fermented by strain AJT can inhibit the growth of mold and coliform bacteria,and can inhibit the acidification of yogurt.Under the condition of strict operation,the shelf life of yogurt fermented by strain AJT can be extended to a period of 42 days at 4 ? and a period of 21 days at 20 ?.4.The room temperature exposure test were studied,compared with the control group,the experience group was extended for 3 days without being contaminated by mold,indicating that the fermented yogurt with strain AJT as the starting strain had the characteristics of inhibiting mold.