Screening Of Yeasts Of Fermented Milk From Sayaram Ketteki And Their Fermentative Properoties

Sayram Ketteki-an alcohol fermented milk is a traditional fermented food from Aksu Area, Xinjiang. This fermented milk tastes chilly, mastic mixed with mellow, texture sticky, and reports that can be pulled out nearly1meter long. Because of its rich flavor and nutrients, the food is loved by local people.In recent years, the development of fermented dairy products market is diverse. The types of products are aboundant. And consumers concern more and more about the product’s safety and nutrition. Their concerns are much more professional and extensive than before. In view that the alcohol fermented milk has a very long history of use in its traditional birthplace, and it is riched in nutrients, so fermentation of this product in controlled process is imperative. And its special flavor and sticky texture will largely enrich fermented dairy products market.But the microflora of this traditional fermented food is very complex. Our laboratory isolated44strains of lacto-bacteria,5strains of yeast. This paper used the five strains of yeast to ferment milk with Lactobacillus helveticus, and ensure the security of the product by molecular identification. And analyze the physico-chemical index during the fermentation process to achieve the traditional flavor and texture of this alcohol fermentation milk.The main research contents and results are as follows:1. The screening and identification of yeast in Sayram KettekiThe separation and isolation of yeasts are taken in the natural fermented Sayram Ketteki,5yeasts are isolated. The result of preliminary microscopic examination to the five yeasts is proved their yeast morphology. In the analyze of preliminary sensory evaluation of these five yeasts, in the form of questionnaires, mainly from the perspective of flavor, according to this results,3strains of yeasts were eliminated. And the molecular identification of the two strains of yeast51-1and51-6are necessary. After the enrichment cultivation, extraction of DNA, PCR amplification, GenBank sequencing and comparison of sequence homology, the result of the molecular identification is that these two strains are both Kluyveromyces marxianus. Their similarities to K. marxianus CHY1612can be reached99%.2. The process of Sayram Ketteki alcohol fermented milkBased on the analyze of pH, acidity, viscocity and Lactobacillus counts, the condition of fermentation of both Lactobacillus helveticus and K. marxianus can be speculate. In the condition of L. helveticus and the yeast51-1, the lactobacillus counts are all above the counts in the condition of L. helveticus and the yeast51-6.Following pH changes in the fermentation process can result that both two strains of yeast and L. helveticus fermented milk, pH reach to4.5approximately in4h to5h. Therefore the fermentation ends are both at4.5h.In order to determine the process of fermentation, the orthogonal test method is used. The four variables are the proportion of inoculation, sugar, the quantity of inoculation and fermentation temperature. In a comparison of four indexes:pH, titratable acidity, viscosity and lactic acid bacteria density under the premise, for the second sensory evaluation, yeast51-6mixed L. helveticus is chosed, with a proportion of inoculation of1:1, a quantity of inoculation of3%, addition of sugar lOg/100ml, and a fermentation temperature40℃. The process has a fermentation duration of4.5h as the best process.3. The research of volatile materials in the alcohol fermented milkThe SPME-GC/MS method is the most popular analyze method of volatile materials. The quantity of volatile materials in the alcohol fermented milk is about40, which are organic acid, hydroxy compound, ketone with medium molecular weight. The2,3-butanedione’s content is about5.31%. Compared with the ordinary yogurt, acid materials in the alcoholic fermented milk are more abundant, including muramic acid, butyric acid,2-methyl propionate, enanthate, hexianoic acid, octanoic acid, naphthenic acid, dodecanoic acid, which explained the alcoholic fermented milk taste is partial acid. As well as in the production process, the addition of sugar or aroma-producing strains should be discussed with importance.