Analysis Of Quality Characteristics And Process Optimization Of Traditional Fermented White Yak Yogurt In Tianzhu Pastoral County

Traditional fermented white yak yoghurt is a mixed fermentation of lactic acid bacteria and yeast,and the microbial species are different depending on the altitude and ecological environment.Due to the lack of uniform standards for production and product quality,the quality varies greatly.In order to standardize and industrialize the production of white yak yoghurt,this paper takes the traditional fermented white yak yoghurt in the typical producing area as the sample,and the common physicochemical index as the control,its conventional physical and chemical indicators,amino acids,trace and heavy metal elements,and volatility.Flavoring substances and rheological properties were determined in detail.On the basis of high-throughput sequencing of white yak yoghurt,the dominant bacteria were separated and screened.The selected dominant strains and Streptococcus thermophilus were used.The response surface design was used to optimize the fermentation conditions of the compound bacteria,and the quality characteristics of the compound yoghurt fermented white yoghurt were compared and analyzed.The research results are as follows:1.The quality characteristics of traditional fermented white yak yogurt.The average protein and fat content of traditional fermented white yak yoghurt was 5.29% and 6.95%,respectively,which was 1.73 and 2.38 times higher than that of commercial yoghurt.The difference of water,ash and total sugar content was not significant(p>0.05).The content of elements were significantly lower than that of common yoghurt(p<0.05);the total amount of amino acids was 4.832 mg/100 g,and the essential amino acids accounted for 32.86% of the total amino acids,of which the highest glutamic acid content was 1.107 mg/100g;The average number of substances detected was 57,which was 24 less than that of ordinary yogurt.Among them,19 were alcohols,29 were esters,and 20 were hydrocarbons,which were significantly higher than ordinary yogurt(P<0.05);ethyl acetate,The average values ??of2-methylbutyraldehyde and isovaleraldehyde RAOV were 36.474,10.998 and 8.078,respectively.The initial shear stress and apparent viscosity are lower than ordinary yogurt;the storage modulus G’ is higher than the loss modulus G",the dominant component is elastic component,which is solid-like;the effect of temperature on shear stress is less than that of ordinary yogurt.2.Study on microbial diversity of traditional white yak yoghurt.The traditional white yak yoghurt bacteria produced 145,653 effective sequences,the high quality sequence accounted for 95.07%;the fungi produced a total of 125,125 effective sequences,and the high quality sequence accounted for 80.44%;the bacterial community dominant gate,the genusthick-walled phylum(Firmicutes)Lactobacillus;the dominant members of the fungal community are Ascomycota and Basidiomycota,and the dominant genus is Inocybe,Tomentella and Wax.(Sebacina).3.Screening of dominant strains of traditional fermented white yak yogurt.A total of 87 strains were isolated,of which 38 were cocci and 49 were bacilli.After screening,4 strains with better performance were obtained.Among them,strain 2(Lactobacillus fermentum)was a dominant strain with high viable count,strong acid production ability,weak acidification ability,large color value change and strong tolerance to adverse environment.4.Optimization of fermentation conditions and quality assessment of the compound bacteria.The response surface optimization results showed that the sensory score was the highest under the condition of dominant bacteria 2(Lactobacillus fermentum): Streptococcus thermophilus 1:0.69,inoculum size 3.24%,fermentation temperature 36 °C.The protein,fat and total sugar in the finished product are 5.79%,5.47,4.73%,the total amount of amino acids is 7.420 mg/100 g,the essential amino acids account for 39.30% of the total amino acids,and the glutamic acid content is 1.728 mg/100 g,which is more than the traditional fermented white yak.The average value of yogurt was 34.88%,6.44% and 35.94% higher.67 kinds of volatile flavor substances were detected,including 14 kinds of alcohols,7 kinds of esters and16 kinds of hydrocarbons;the acetaldehyde and diacetyl RAOV values ??were 6.22 and31.05,respectively.The initial shear stress and apparent viscosity are higher than traditional fermented white yak yoghurt,and the effect of temperature on shear stress is smaller than that of traditional fermented white yak yoghurt.The above results show that the yoghurt fermented by the compound strain retains the unique flavor of the traditional yoghurt,and the total amount of amino acids,essential amino acids,total amino acids,glutamic acid content,rheological properties,and quality are more.