| Adherence is the primary prerequisite for pathogenic bacteria to colonize host cells and exert their physiological effects,as well as the first step in pathogenesis.If the adhesion of pathogenic bacteria to enterocytes can be blocked,the infection and i nvasion of pathogenic bacteria can be effectively prevented and the morbidity rate can be reduced.Yeast cell wall polysaccharides are functional polysaccharides,mainly including dextran and mannans,which have physiological functions such as immunity enhancement,antioxidant,antiviral,gastrointestinal tract health modification,and animal production performance improvement.The monosaccharide composition,purity,molecular structure,molecular weight and other characteristics of polysaccharides can affect their physiological functions,and these characteristics are related to their preparation conditions.In this study,mannan and dextran were prepared using Saccharomyces cerevisiae and their physicochemical properties were analyzed;yeast cells were used as adhesion medium instead of intestinal cells,and the effects of yeast strain,preparation method,molecular weight and other factors on the adhesion inhibition of E.coli and Salmonella were studied;the adhesion inhibition rate of dextran was determined by fluorescence quantitative PCR,and the effects of yeast strain,preparation method and dextran concentration on the adhesion inhibition of dextran were studied.The effects of yeast strain,preparation method and dextran concentration on the inhibition of adhesion of Escherichia coli and Salmonella were investigated.The main findings of the study are as follows:(1)Preparation and analysis of yeast cell wall polysaccharides.Saccharomyces cerevisiae was used to prepare mannans and dextrans and analyze their physicochemical properties.The purity and protein content of mannans prepared by different yeast strains differed greatly.The purity of mannans prepared by the acid method was higher than that of the alkaline method and the high-temperature extraction method.The solubility of mannan prepared by Saccharomyces cerevisiae BY5 was significantly higher than that of other strains.The solubility of mannans prepared by acid and alkaline methods was significantly greater than that of high-temperature extraction.Yeast strain and preparation method hardly affected the viscosity of mannan solution.The p H values of mannan and dextran of different yeast strains and preparation methods were significantly different.The protein content,fat content,water-holding power and oil-holding power of dextran were significantly different depending on the yeast strain and preparation method.Infrared spectroscopy analysis showed that the molecular structures of mannan and dextran and the groups on them were significantly different among different yeast strains and preparation methods.(2)Study on the inhibition of Escherichia coli adhesion to yeast cells by mannan.A microscopic observation method for evaluating the depolymerization activity of mannan was established using yeast cells instead of intestinal cells as the adhesion medium,and a digital quantitative evaluation of the effect of mannan on inhibiting E.coli adhesion was achieved.Among the five strains of Saccharomyces cerevisiae studied,mannan M5 prepared by Saccharomyces cerevisiae BY5 showed the highest depolymerization activity of 83.85%.The depolymerization activity of mannan prepared by high-temperature extraction was much higher than that of acid and alkaline methods.In the range of 0.2mg/m L～0.8 mg/m L,the higher the concentration of mannan,the stronger its depolymerization activity in a concentration-dependent manner.The smaller the molecular weight of mannan,the better its depolymerization activity.The depolymerization activity of mannans was much higher than that of oligofructose,chitosan and xanthan gum.(3)Study on the inhibition of Salmonella adhesion to yeast cells by mannoprotein.Using yeast cells instead of intestinal cells as the adhesion medium,a microscopic observation method was established to digitally and quantitatively evaluate the effect of mannan inhibition of Salmonella adhesion.Among the five strains of Saccharomyces cerevisiae experimented,the highest depolymerization activity of 73.58% was obtained for mannan prepared by BY5.The best depolymerization activity of mannan prepared by high-temperature extraction was followed by the alkaline method,and the worst by the acid method.The depolymerization activity of Salmonella spp.of mannan was concentration dependent in the range of 0.2 mg/m L to 1.0 mg/m L.The smaller the molecular weight of mannan,the better its Salmonella depolymerization activity.The depolymerization activity of mannan was much higher than that of polysaccharides such as oligofructose.The inhibition of adhesion of mannan to E.coli was significantly better than that of Salmonella.(4)Study on the inhibition of adhesion of E.coli and Salmonella to Caco-2 cells by yeast dextran.The inhibition rate of adhesion of dextran prepared by different yeast strains to E.coli and Salmonella varied significantly,and among the five experimental strains of Saccharomyces cerevisiae,the inhibition of adhesion of dextran prepared by BY1 was the best.The inhibition of adhesion of dextran to E.coli was better than that of Salmonella.Compared with the acid and alkaline methods,the dextran prepared by high-temperature extraction method had the best adhesion inhibition effect,and its adhesion inhibition rate of E.coli and Salmonella was 77.45% and 49.84%,respectively.In the range of 0.2mg/m L～0.8 mg/m L,the inhibition of adhesion of dextran to E.coli and Salmonella showed concentration dependence.Yeast dextran was significantly more effective in inhibiting the adhesion of E.coli and Salmonella to Caco-2 cells than yeast cells and yeast cell walls.The adhesion inhibition ability of mannan was significantly higher than that of dextran.No synergistic effect was found when mannan was shared with dextran. 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