Isolation And Identification Of Eps Producing Lactic Acid Bacteria From Sayram, Traditional Xinjiang Ropy Yoghurt, And Its Role In Fermentation Process

Sayram yoghurt (Sayram Ketteki), mainly produced in Aksu City, is one of the most popular and traditional fermented dairy products of Xinjiang. The product is produced by natural fermentation process using a certain temperature. The process is completed in about8h to obtain viscous, flexible, white-colored, and sour product. The lactic acid bacteria improve the nutritional value, enhance sensory properties of products, and help in promoting the body’s digestion and absorption. Fermentation process caused by lactic acid bacteria makes a sticky and elastic product. The yoghurt can be pulled out one meter-long just like a wire, and hence it is also known as ropy yoghurt. There are some reports from Japan and other countries about the production of traditional ropy yoghurt along with isolation and identification of strains responsible for ropiness. However, there is no any literature available on the production and isolation of strains from sayram yoghurt of Xinjiang.1. Firstly, the yoghurt was analyzed for different microbial indicators (lactic acid bacteria, yeasts and molds, coliform bacteria). The results showed that number of lactic acid bacteria (108CFU/ml) in yogurt were higher than the national standard (106CFU/ml) of lactic acid bacteria. The yeast count was104CFU/ml on brilliant green lactose bile (BGLB). However, no mold colonies were observed in the yoghurt samples using potato-dextrose agar (PDA).44lactic acid producing bacteria were isolated for their viscosity and EPS production from3samples of sayram yoghurt, traditional ropy yoghurt of Xinjiang. Only two high yielding EPS producing lactic acid bacteria were isolated from single and mixed fermentation of milk. The bacteria were screened by biochemical tests through API identification system, and by molecular biological techniques through16S rDNA analysis. The results showed that the two strains are Lactobacillus helveticus and Streptococcus thermophilus. 2. Change in pH, total acidity and viscosity of sayram production using single and mixed fermentations system was evaluated for24h. Experimental results show that mixed fermentation process promoted strain growth, acid production, and produced sticky, elastic product with excellent features.3. The physicochemical characteristics including ash, fat and protein, and extracellular polysaccharide content of sayram yoghurt was evaluated. The use of phenol-sulfuric acid method for the determination of extracellular polysaccharide content confirmed the role of lactic acid bacteria in the production of ropy sayram yoghurt. The appropriate proportion of isolated lactic acid bacteria, temperature and sugar for good quality sayram production was investigated. The results reveal that3%lactic acid culture (2%Lactobacillus helveticus&1%Streptococcus thermophilus),10%sugar and fermentation temperature40℃gave the most acceptable sayram yoghurt with good sensory attributes.