Study On Isolation, Identification And Properties Of Kluyveromyces Marxianus From Deteriorative Yogurt

In many foods, dairy products are closely interrelated to the people's daily life, no doubt it is an important "vegetable basket" products, as well as it is an important part of the profits can generate income for our country. In recent years, with the rapid development of acid dairy products, as a typical representative of dairy products, the quality and security of yogurt has gradually become the focus of the public. With the substantial increase in yogurt production, yeast become the dominant micro-organism that leading to metamorphic yogurt, and become a major limiting factor of yogurt shelf life.In this study, we collect samples from different types of yogurt, and get 8 stains. Then, compare the gas production, experimentize physiological and biochemical identification and molecular identification. After comparing the gas production, ultimately determine 8 strains that can cause deteriorate of yogurt. At last a yeast which will caused up package of the yogurt is finalized, named No. L-6.Identification of physiological and biochemical test results as follows, Carbohydrate fermentation tests, can be fermented glucose, sucrose, maltose, lactose, galactose non-fermenting; carbon source assimilation tests, can be assimilated raffinose, galactose, maltose, sucrose, cellobiose, lactose, D-xylose, succinate, mannitol, and inositol different, ribose, erythritol, rhamnose, ribose alcohol, citric acid, soluble starch, arabinose, trehalose; nitrogen assimilation tests, can not assimilate nitrate, can be assimilated triethylamine hydrochloride, hydrochloric acid cadaverine; can not breed in the absence of vitamin growth medium; can not grow 50% (w/w) glucose yeast extract medium; 37℃can grow; can be grown under 100 mg/L of cycloheximide. Reference to "The Yeasts: a taxonomic study" (fourth edition), It is primarily identified as Kluyveromyce marxianus.Identification of the molecular level for their experiments, the yeast species was used to identify. On the current international generic 26S rDNA D1/D2 region is used for molecular identification. Their results show that the strain was amplified 26S rDNA D1/D2 region sequence with the GenBank report on Kluyveromyces marxianus 26S rDNA D1/D2 region 99% homology. As a result, Kluyveromyces marxianus was further confirm on the level of molecular biology. In the course of molecular identification, the effect of 5 methods of DNA extraction from heat-resisting yeast in deteriorative yogurt were compared. A efficient extraction procedure was confirmed for extracting yeast DNA from deteriorative yogurt.In order to control the strain, extend the shelf life of yogurt, cleansing and disinfection of equipment, as well as analysis of the sources of its pollution, its physiological characteristics and the decimal reduction time was studied: the suitability of its growth temperature and pH was determined; studied the temperature and pH value on the impact of the growth curve; studied acid strains; resistant sugar; high temperature and low temperature growth characteristics. The results show that the appropriate growth temperature is 36℃, suitable pH value for the growth is 5.5, the temperature impact on the growth curve significantly, pH of the growth curve is not significantly; will fermentation in 50% (w/w)of glucose solution; The maximum growth temperature is 54℃, the lowest growth temperature is 6℃.The results of decimal reduction time of the strain: sterilization when rapid warming, 60℃180 s, decimal reduction time is 1.319, 75℃180 s, decimal reduction time is 1.063, 80℃for 180 s bacterial sterilization were killed; gradually warming to when required sterilization temperature sterilization, 60℃300 s, decimal reduction time is 1.849, 75℃300 s, decimal reduction time is 1.173, 80℃for 300 s bacterial sterilization were killed. The factory for sterilization's temperature and time is 95℃300s, therefore we found that the effect of direct sterilization is obviously better than the effect of warm-up to the bactericidal temperature, also it can be speculated that the yeast is contaminated after the sterilization process to Yogurt's.