Isolation And Identification Of Microflora In Yak Milk Dreg Of Tibet In China And Screening Of Fine Lactic Acid Bacteria

Yak milk, as a kind of very precious and rare milk, has been regarded as an natural, greenand healthy organic food with the broard market development value. With people`s growingdemand for health, high quality food in recent years, yak milk products of no pollution, highlatitudes and high altitude have increasingly aroused widespread public attention. Yak milkdreg, as the Tibetan herdsmen’s important protein source, was produced by naturallyfermentation, and is rich in microbial resources and also an important source of fine lacticacid bacteria strains. But till now, most lacal featured fermented dairy products have not beenfully understood and explored. This paper aims to study the physical and chemical propertiesof yak milk in Tibet and the unique lactic acid bacteria (LAB) and yeast resources of yak milkdreg. All the microflora were identified based on phenotypic characterization and analysis ofgene sequences; The LAB strains were screened through preliminary selection by geneticstability, curd time, titratable acidity and structural state and then further screening wasperformed through growth and fermentation performance, capacity of incense and sensoryevaluation to obtain the best strain resources suitable for the production of fermented milk.The main conclusions are as follows:(1) The average content values of protein, fat, lactose, non fat milk solids, ash andmoisture were4.36±0.19g/100g,5.96±0.33g/100g,6.00±0.06g/100g,7.93±1.80g/100g,0.84±0.04g/100g and85.80±1.70g/100g, respectively. The concentration of main indexessuch as total solids (TS), protein, fat and lactose representive of the milk resourcecharacteristics were higher than that of cow and goat milk.(2) The LAB population in the yak milk dreg samples was from3.86to6.89logcfu/gwith an average concentration of5.19±0.93logcfu/g, while the average concentration of yeastpopulation was4.69±1.26logcfu/g ranging from3.08to6.81logcfu/g. The count of LAB ofall the ten samples were higher than those of the yeast except one sample and the LABpopulations in wet samples were significantly higher than those of dry samples (P<0.05).(3) One hundred and thirteen LAB strains and Ninety-one yeast colonies were isolatedfrom ten yak milk dreg samples. The LAB strains were identified belonging to five generaand thirteen different species. P. pentosaceus (3). Enterococcus (47.79%) and Lactobacilli(45.13%) were dominant over the species which were Ec. durans (29.20%), Lb. paracasei ssp. paracasei (20.35%) and Ec. faecium (16.81%). The yeast was identified to belong to sevengenera and ten different species. P. fermentans（20.88%）, S. cerevisiae (19.78%), K. lactis(16.48%), R. mucilaginosa (14.29%) and K. marxianus (12.09%) were the most commonculturable species.(4) Four strains of better genetic stability, less curd time and better structural state lacticacid bacteria (LAB) were obtained from the isolated LAB strains. Two strains were cocci,which have been identified as Ec.durans, while the other two strains were Lb. paracasei ssp.paracasei. Then the best strains combination were selected by further analysis, which wasCD1:1, Ec.durans：Lb. paracasei ssp. paracasei=1:1.