Study On Microbial Flora And Antioxidant Activity Of Natural Fermented Yak Yogurt

As a sort of traditional fermented dairy products with local characteristics, yak yogurt is very popular. It is mainly made by yak herders of the main producing area in traditional fermentation methods,with unique flavor, nutrient-rich and some health functions.Such health care function may have great relationships with its microbial flora.Because of different geography and climate of regions, fermentation temperature, time and producing methods, yak herders'living habits, milking equipment and the fermentation vessel,ect., there are some differences of the advantages of micro-organisms among regional natural fermentation yak yogurt, but mainly lactic acid bacteria (LBA)LBA can not only improve the flavor of food, improve food nutritional value, storage performance and value, it also has a variety of physiological functions shown by a large number of studies, such as promoting the decomposition and absorption of food nutrients,regulating the body's normal flora of the gastrointestinal tract to maintain and improve the body's normal function, lowering serum cholesterol, enhancing immunity, antioxidant activity and so on. Late starting of the study on LBA in China,we have few independent intellectual property rights of LBA and its preparations. Its application is minimal. This study began in this context.Using yak yogurt made in Tibet and western Sichuan of Tibetan Plateau by Tibetan nomads as study Object.this paper mainly analyzed and identified the preponderant micro-organisms, and isolated some good bacteria to provide theoretical basis for industrial production of traditional yogurt,and to lay a foundation for the establishment of yogurt Microbial Resources of the Tibetan Plateau and even the whole Coutry. Test results are as follows:(1) Study on naturally fermented yak milk samples have shown that microorganism numbers of the 10 samples from Tibet and western Sichuan Plateau were high.Most were LBA with 107cfu/g or more viable cells numbers; followed by yeast, while yeast cell counts of samples from Tibet regions wer generally higher than that from western Sichuan, the former wer 106cfu/mL and the latter between 105 to 106cfu/mL.(2) 15 strains of LBA were isolated and identified from 10samples, of which 8 strains of Lactococcus, namely:L.mesenteroides subsp.mensenteroides, S.ferus, S.thermophilus, L.raffinolactis, S.salivarius, L.lactis subsp.lactis, L. lactis and L.mesenteroides subsp.dextranicum; bacilli 7, namely:L.oris, L.fermentum, L.casei, L.plantarum.L.delbrueckii subsp.lactis, L.brevis and L.helveticus.(3) 8 strains of yeast were isolated and identified from 10samples. namely:C.ethanolica, H. marxianus, S.cerevisiae, B.claussenii, C.sake, P.fermentans, H.anomala and B. lambicus.(4) Using the 15 strains of LBA asolated as objects, determined their antioxidant activity. The results showed that 15 strains had different levels of antioxidant activity with 5 indicators: in the tolerance of H2O2, the ability of clearing superoxide radical (O-2-),chelating ability of Fe2-,the ability of preventing lipid to peroxide and clearing ability of DPPH radical. Strain DX-1, DX-3 and DLDQ1-1 shown high antioxidant activity in all measured indicators and had value of further research and development.