Screening Of Potential Profitable Yeasts In Xinjiang Kazak Cheese And Manufacture Of Flavor Milk Tablets

In recent years,probiotics have become more and more widely used in the food industry.Various kinds of probiotics such as yogurt,yoghurt and other dairy products have been successively developed and marketed.The addition of probiotics not only gives the product a good taste and taste,but also greatly enhances the nutritional quality of the product.At present,there have been some reports about probiotic milk tablets at home and abroad.Probiotic milk tablets are rich in nutrients in milk and have probiotic effects.They have numerous flavors,attractive novelties,and a large audience.However,most of the currently available probiotic additives on the market are Lactobacillus,Bifidobacterium,Streptococcus,etc.,which makes the product's flavor and texture too similar,which has caused people to gradually drink fatigue for such products.Recently,researchers have discovered that there are also many bacteria with probiotic properties in yeast,and the addition of these probiotic yeasts can make the flavor of dairy products become more distinctive and the nutrient composition is also improved.In Xinjiang,the Kazakh herdsmen lived and grazing on the lower reaches of the foothills of the Tianshan Mountains all year round.Their handmade cheeses are unique in flavor,rich in nutrition,and contain a large amount of yeast strains.In this thesis,Kazakh cheese was used as the raw material to isolate and identify the yeasts during the maturation process,and some yeasts with potential probiotic properties were selected and co-fermented with lactic acid bacteria to produce special probiotic flavored milk tablets.The specific findings were as follows:(1)74 strains of yeast were isolated from home-made cheese in the Kazakh agglomeration area in northern Xinjiang,and 18 yeast strains with high activity were identified based on the ITS sequence.The results showed that among 18 strains of yeast,The strains H1,Y2,L1,N2,F1,and L5 belong to Kluyveromyces marxianus;L3,Y1,and H6 belong to Saccharomyces cerevisiae;H2 and N9 belong to Candida glauca;N fragrances belong to Corynespora spp.;L3,F3,N6,N1,L4,and Y36-6 belong to Pichia kudriavsi.(2)The selected 18 yeasts were subjected to a subsequent probiotic screening test.By analyzing the probiotic characteristics of 18 strains with different bile salt concentrations,different pH values,simulated human gastric juice and human body temperature conditions,and using Escherichia coli and Staphylococcus aureus as indicator bacteria,their ability to inhibit harmful bacteria was studied.The surface hydrophobicity and automatic aggregation ability of the strains were also measured,and the probiotic properties of the strains were systematically analyzed.The results showed that 4 strains(Y1,H1,Y36-6,and L4)obtained from 18 strains of yeast had good survival rate under the above conditions and were potential probiotic yeasts.Physiological and biochemical tests and 26S rDNA sequence alignment analysis were performed on the 4 strains.The H1 strain belonged to the genus Kluyveromyces with a similarity of 99%.The strain Y1 belongs to the genus Saccharomycete and has similarity.99%,Y36-6 and L4 belong to Pichia kudriavzevii with a similarity of 99%.Through the analysis and optimization of fermentation characteristics,yeast L4 with good fermentation characteristics was selected for the subsequent production of probiotic yeast flavored milk tablets.(3)The yeast L4 with unique flavor and probiotic properties was deposited at the CCTCC under the code number CCTCCM2017759-L4.The probiotic bacteria flavored milk tablets were prepared by co-fermentation with yeast and lactic acid bacteria.The optimum fermentation process was shown to be:fermentation temperature 37?,inoculum ratio(lactic acid bacteria)1:3(yeast),sugar content 11%,fermentation time 10 h.A comparative analysis of the flavor components of milk tablets showed that the probiotic yeast milk tablets had more alcohol and ester substances than blank control milk tablets.The flavor substances were relatively abundant,and the acid sweetness and taste were also better.The initial probiotic bacterial count of finished milk tablets was 2.62×10~100 cfu/g,and after 60 days it was 1.66×10~8cfu/g,which had a high survival rate.At the same time,the health indicators,physical and chemical indicators,and microbiological indicators of the finished milk tablets were tested with reference to the national standards for probiotic dairy products.The results showed that the physical and chemical indicators,appearance,and color were all in compliance.