Study On The Symbiosis Of S.Boulardii And Lactic Acid Bacteria And The Co-Fermented Milk

At present,the probiotics contained in commercially available fermented milk are mainly lactic acid bacteria,which have similar probiotic effects on human body.In order to improve the nutritional value and probiotic function of fermented milk,multi-strain fermentation is the development trend of fermented milk.In this study,Saccharomyces Boulardii combined with lactic acid bacteria fermented milk was used to develop a kind of fermented milk with unique flavor,probiotics rich in different probiotic functions and high nutritional value to meet consumers'higher demand for food nutrition.Therefore,this study screened lactic acid bacteria with potential symbiosis with Saccharomyces Boulardii,studied the symbiotic relationship between Saccharomyces Boulardii and Lactobacillus Casei,and optimized the optimal fermentation conditions of Saccharomyces Boulardii combined with Lactobacillus Casei fermented milk,the quality of co-fermented milk was evaluated.The main results are as follows:1.The effects of Saccharomyces Boulardii metabolites on the growth of three lactic acid bacteria,including Bifidobacterium,Lactobacillus Casei and Lactobacillus plantarum,were studied with the number of pH and the number of viable lactic acid bacteria.The results show that the metabolites of Saccharomyces Boulardii can promote the growth of BifidobacteriumLactis,Lactobacillus Casei and Lactobacillus Plantarum,and enhance their acid production ability.Among them,the metabolites of Saccharomyces Boulardii have the strongest promotion effect on Lactobacillus Casei,metabolites of Lactobacillus Casei have the most significant promotion effect on Saccharomyces Boulardii.Therefore,Lactobacillus Casei was selected for subsequent tests.2.Using the optimal potential symbiotic lactic acid bacteria-Lactobacillus Casei and Saccharomyces Boulardii to ferment skim milk,observe pH,lactic acid bacteria viable number,Saccharomyces Boulardii viable number,ethanol content,water holding capacity,the symbiotic relationship between Saccharomyces Boulardii and Lactobacillus Casei was evaluated from three aspects:inoculation amount,fermentation temperature and fermentation time of Saccharomyces Boulardii.The results showed that the 10~4CFU/mL inoculation of Saccharomyces Boulardii had the most obvious symbiotic effect on Lactobacillus Casei.Excessive inoculation of Saccharomyces Boulardii would lead to interspecies inhibition,and too little would lead to weakening of interspecies symbiosis;fermentation temperature has a significant effect on the symbiotic relationship between strains,38?Saccharomyces Boulardii has the most obvious symbiotic effect on Lactobacillus Casei,too low fermentation temperature will weaken the symbiotic effect between strains,resulting in insufficient fermentation of samples;fermentation time is an important factor affecting the symbiotic relationship.Saccharomyces Boulardii has no obvious promotion effect on the growth of Lactobacillus Casei after 16h,the growth of Lactobacillus Casei was obviously promoted by Saccharomyces Boulardii at 16-28h of fermentation.3.Using response surface design and sensory evaluation,the optimal fermentation temperature,fermentation time and yeast inoculation amount of co-fermented milk by Saccharomyces Boulardii and Lactobacillus Casei were optimized.The results showed that the optimal fermentation temperature of co-fermented milk was 38.5?,the optimal fermentation time was 25.5h,and the optimal yeast inoculation amount was 1.6×10~3 CFU/mL.The optimized fermented product has bright color,pleasant smell,uniform state and fine taste.4.Under the best fermentation conditions,Saccharomyces Boulardii and Lactobacillus Casei co-fermented milk,compared with Lactobacillus Casei fermented milk alone,from electronic tongue taste,pH,acidity,water holding,the quality of yoghurt fermented by Saccharomyces Boulardii combined with Lactobacillus Casei was evaluated by gel characteristics,viable count,chromaticity,amino acid content,oxidation resistance,volatile components and microstructure.The results showed that the combined fermentation sample had attractive color,higher fresh aftertaste and sour taste,and better taste.The quality of fermented milk was obviously improved through combined fermentation,and the acidity decreased by 48.57%,22.06%viscosity decreased,water holding capacity increased by 74.02%,gel strength increased by 20.23%,lactobacillus casei increased by 98.92%,Saccharomyces Boulardii reached 6.6×10~6 CFU/mL;the results of antioxidant experiments suggest that combined fermentation can enhance the antioxidant function of fermented milk;The volatile flavor substances in co-fermented milk mainly include acids,esters,alcohols,aldehydes,ketones and furans.Among them,acids,the proportion of alcohols increased significantly,while esters and aldehydes decreased.The difference between the total amount of amino acids in co-fermented milk and Lactobacillus Casei fermented milk alone was not obvious,which would not lead to the loss of amino nitrogen content in the combined fermentation process.To sum up,this study screened out Lactobacillus Casei with good symbiotic relationship with Saccharomyces Boulardii,and optimized the best conditions for the co-fermented milk of Saccharomyces Boulardii and Lactobacillus Casei,the quality of combined fermentation milk by Saccharomyces Boulardii and Lactobacillus Casei was evaluated to provide certain data support and theoretical reference for the development of a multi-strain fermented milk with unique flavor and better probiotic functional characteristics.