Identification And Characterization Of The Yeast Stains Isolated From Koumiss

In order to explore the microbial resources in koumiss,a traditional fermented dairy product,yeast strains were isolated from koumiss samples from six different regions.The primary screening indicators were ethanol production,aroma production and biogas production properties.The second screening was based on tolerance performance,i.e.acid resistance,temperature tolerance,glucose tolerance,lactose resistance and ethanol tolerance.The yeast strains with good tolerance performance were identified,which their growth and fermentation characteristics were also examined.The results were as follows:47 strains of yeasts were isolated from koumiss samples.14 strains of yeasts with good fermentation performance were screened through colony morphology,gas production,aroma production and ethanol production.5 yeast strains(A412,E25,F2,H61,P2)were well tolerated by rescreening had better tolerance performance at pH 1.0,temperature(10°C/45°C),glucose concentration 70%,lactose concentration 60%.Strains P2 had better tolerance performance at ethanol concentration 16%,Strains A412,F2 and E25 had better tolerance ethanol concentration 14%.Strain H61 had better tolerance performance at ethanol concentration 12%.Combined with morphological observation,physiological-biochemical tests and ITS sequence identification,5 yeasts were divided into two genera: Pichia pastoris and Saccharomyces cerevisiae.Strains A412,E25,F2,H61 were identified as Pichia manshurica and P2 was identified as Saccharomyces cerevisiae.Through the experiment of growth and fermentation characteristics,5 strains grow up at the lag phase in 0-2 h at 28°C incubation,and the pH value remained steadily.E25 reached logarithmic phase at 2-6 h,F2 and H61 were 2-8 h,and p H value were decreasing rapidly.The viable count of A412,F2,E25,H61 all reduced after 20 h and pH values bacame steady.P2 grew slowly after 14 h and its stationary phase remained long.The fermentation abilies of A412,E25,F2,H61 were similar,which were superior to the fermentation capacity of P2.Therefore,the growth condition and the fermentation capacity of the same species were basically the same.