Screening Of Lactic Acid Bacteria Starter In Xinjiang Kazakh Traditional Cheese And Its Effect On Cheese Flavor

Cheese is one of the most characteristic homemade fermented dairy products of the Kazakh people in Xinjiang.The herdsmen on the grassland use the method passed down by their predecessors to make cheese.This unique craftsmanship is the difference between Kazakh cheese and other cheeses on the market.One of the factors;Kazakh traditional cheese also contains local rich lactic acid bacteria resources,lactic acid bacteria can play a health care role in the body's metabolic function.In recent years,with the development of the economy,people's demand for cheese has begun to increase year by year,and cheese has begun to be industrialized.In the long run,the loss of microbial resources in such traditional cheeses will be caused.In this study,three cheese samples collected from three counties in the Yili area of Xinjiang were treated,and the lactic acid bacteria were isolated by a traditional separation method,and the isolated and purified strains were sent for molecular biological identification to identify the lactic acid bacteria.The test was carried out to prepare a composite starter by screening bacteria with excellent functional properties,and used in the simulation of Kazakh traditional cheese processing to analyze the influence of the composite strain on the flavor of the traditional Kazakh cheese.The specific research results are as follows:(1)Twenty suspected lactic acid strains were isolated and screened from three hand-made traditional cheeses from the Kazakh family in Yili,Xinjiang.Molecular identification of D-12 and S-2 are Streptococcus thermophilus;D-14 and B-12 are Lactobacillus casei;D-2 and D-1 are Lactococcus garvieae;S-7 and B-10 are Lactobacillus helveticus;S-4,D-4,D-6 and D-7 are Enterococcus faecalis;B-6 and D-8 are Lactobacillus rhamnosus;B-9,D-16 and D-15 are Lactococcus lactis;S-3,D-11 and D-12 are Leuconostoc lactis.(2)According to physiological and biochemical and observation of single colonies,8 strains of lactic acid bacteria D-12(Streptococcus thermophilus),D-14(Lactobacillus casei),D-2(Lactococcus garvieae),S-7(Lactobacillus helveticus),S-4(Enterococcus faecalis),B-6(Lactobacillus rhamnosus),B-9(Lactobacillus lactis),S-3(Leuconostoc lactis)for acid resistance Excellent lactic acid bacteria D-14,D-2,S-7,S-3 were obtained by measuring bile salt,simulated gastric juice,surface hydrophobicity,ability to degrade nitrite,bacteriostasis and enzyme production.(3)The selected excellent lactic acid strains D-14,D-2.S-7 and S-3 were respectively Y1(D-14: D-2: S-7 = 1:1:1),Y2(D-14: D-2: S-3 = 1:1:1),Y3(D-14: S-7:S-3=1:1:1);Y4(D-2:S-7:S-3=1:1:1)compounding of these four methods,in the fermented milk of these four starter Determination of viscosity,diacetyl,pH 4.6 soluble nitrogen,Y4(D-2:S-7:S-3)is the best compounding starter,and then the pH of the fermented milk of Y4 starter is released.Determination of the amino acid and pH 4.5 soluble nitrogen determined that the optimum addition amount was 5.5%.The optimum starter is applied in the optimum amount of Xinjiang Kazakh traditional cheese to simulate the sensory determination of the Kazakh traditional cheese ripening period.The basic components are determined,including moisture content,protein content,fat content,free fatty acid.Content and pH.Through the above studies,it is found that the simulated Kazakh traditional cheese can reach maturity in 50 days.The basic components of this cheese have been found to have certain regularity at all time points in the mature period,and mature in the sensory evaluation test.On the 50 th day,the score is the highest.At this time,the flavor is at its best,the milk is rich in flavor,and the tissue is fine.The whole piece of cheese is yellow from the inside out.Finally,the volatile flavor substances in the Xinjiang Kazakh traditional cheese were simulated,and a cheese using the common starter of the market was used as a control group for simulating Kazakh traditional cheese.After comparison analysis,it was found that the Xinjiang Kazakh traditional flavor cheese was 40 kinds of volatile flavor substances,including 10 kinds of alcohol volatile flavor substances,12 kinds of ester volatile flavor substances,8 kinds of aldehyde volatile flavor substances,and 4 kinds of acid volatile flavor substances.There are 4 kinds of volatile flavor substances in the same kind,and 2 kinds of other volatile flavor substances.