| In order to optimize the yeast probiotic pathogen of digestive tract and explore its resistance mechanism,in this paper,we studied 7 strains of Saccharomyces cerevisiae,which were isolated from the intestinal tract of duck.First,we screened the strains with high acid resistance and bile acid resistance,and investigated the relationship between Na~+,K~+concentration as well as the activity of H~+-ATPase and the pH value of yeast cells.Second,we investigated the relationship between plasma ATPase activity and intracellular trehalose content in yeast cells and yeast bile salt tolerance in yeast cells under high concentration of bile salt.Then the surface hydrophobicity and the auto-aggregation ability of the seven tested yeast were studied by turbidimetry.The contents and results of this study are as follows:1.The study of the acid stress tolerance of yeast probiotics under different pH stress and its mechanism,experiment results showed that:(1)Through the spread plate count,in the 7 strains of Saccharomyces cerevisiae,the survival rates of the strains WHY-2 and WHY-7 were more than 90%in the environment of pH 2.0 and the survival rate at p H 3.0 was more than 95%at pH 4.0 Survival rate of more than 98%which was higher than the remaining five strains.(2)When the activity of H~+-ATPase in Saccharomyces cerevisiae was tested,we found that it was negatively correlated with environmental p H,the highest act ivity at p H2.0,the lowest activity at pH5.5,and the yeast strain WHY-2 and WHY-7 were higher than those of others.(3)Then we measured the concentrations of Na~+,K~+in the supernatant of Saccharomyces cerevisiae culture solution in different p H environment by air acetylene flame atomic absorption spectrometry.With the decrease of p H,the concentration of Na~+and K~+in 7 strains of Saccharomyces cerevisiae were significantly changed.The concentrations of Na~+,K~+decreased with the decrease of p H value.2.We studied the tolerability of yeast probiotics in different concentrations of cholate and its mechanism.The results showed that:(1)In tolerance test of acid stress in Saccharomyces cerevisiae adapting the method of spread plate count,In the 7 strains of Saccharomyces cerevisiae,the survival rate of WHY-1 and WHY-4 was lower in the environment of 0.3%The survival rate of other strains was higher than 90%,WHY-2,WHY-6,WHY-7 in 0.6%cholesteric acid culture survival rate is still more than 90%.(2)The intracellular trehalose accumulation in Saccharomyces cerevisiae was measured by anthrone colorimetry under different bile acid concentrations.7 strains of Saccharomyces cerevisiae trehalose accumulation decreased with increasing salt concentration of cholic acid,compared with the other 4 strains,WHY-2,WHY-6 and WHY-7 got higher intracellular trehalose accumulation in different bile salts concentration.The intracellular trehalose accumulation in Saccharomyces cerevisiae was measured by anthrone colorimetry under different bile acid concentrations.7 strains of Saccharomyces cerevisiae trehalose accumulation decreased with increasing salt concentration of cholic acid,compared with the other 4 strains,WHY-2,WHY-6 and WHY-7 got higher intracellular trehalose accumulation in different bile salts concentration.(3)The activity of ATPase was measured in the plasma membrane of Saccharomyces cerevisiae,and it was found that it had a positive correlation with the concentration of bile salt.The activity of bile acid was 0.6%and the activity was the lowest when the concentration of bile salt was 0%.It was concluded that the expression of ATPase was increased when the Saccharomyces cerevisiae grew in the high concentration of cholic acid,and the activities of yeast strains WHY-2,WHY-6 and WHY-7 were higher than those of other strains.3.We studied the hydrophobicity and auto-aggregation ability of seven strains of Saccharomyces cerevisiae.The results showed that:(1)The hydrophobic capacity of WHY-6 was 73.71±1.09%,the hydrophobicity of WHY-4 was 4.49±0.76%,and the other five brewer's yeast WHY-1,WHY-2,WHY-3,WHY-5 and WHY-7 The hydrophobicity was 41.62±0.46%,60.63±0.92%,37.10±0.69%,46.20±0.87%and 68.72±0.48%,respectively.Among them,the hydrophobicity of strain WHY-7 and WHY-2 was after that of WHY-6,and the hydrophobicity of WHY-3 and WHY-5 yeast strains was similar.(2)The self-enrichment percentage of the seven strains of Saccharomyces cerevisiae ranges from 96.68±0.46%of WHY-5 to 98.99±0.78%of WHY-2,all reaching the maximum.(3)After 2hs of settling,the percentage of self-aggregated strains of Saccharomyces cerevisiae varied greatly from 24.06±0.70%of WHY-1 to 36.86±0.20%of WHY-7.After settling for 4 h,the 7 strains of Saccharomyces cerevisiae were rapidly and automatically collected,and the percentages of WHY-2,WHY-5 and WHY-7 were significantly higher than those of the other four. |
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