Study On Evaluation Method Of Fresh Milk Quality Based On Genetic Mutation

High-quality milk is the inevitable development direction of dairy industry in China,which makes detection methods of raw milk quality necessary.In recent years,molecular biology method has been developed rapidly in the field of food,meanwhile,the use of molecular biology methods to identify the quality of milk has become a trend.Therefore,this study used raw milk samples from about 500 cows as raw material,and raw milk samples from the same cow's were divided into two groups,the one group was used to detect the content of milk fat,milk protein and lactose,somatic cell count(SCC),total solids content and fat-protein ratio,the other group was used for DNA extraction.And the functional genes closely related to the quality of milk were screened,including STAT5A,CLU,IGF2 and BAF60c.Also specific primers were designed to amplify the four functional genes,followed by the identification of mutation sites and its genotype using direct DNA sequencing and restriction endonuclease digestion.Finally,the relationship between genotype and quality of milk was established,and it was supposed to pre-evaluate milk quality by observing genotypes on the mutation and provide a new method for assessment and classification of milk quality,also in expection of providing reference for the production of high-quality dairy products and a new method for milk quality testing.The main results were as follows:1.Evaluation method of fresh milk quality based on mutation of bovine STAT5A gene.The C6853T mutation on exon 7 of STAT5A gene was identified for genotyping,and the three genotypes of CC,CT and TT presented a significant correlation with the content of milk protein and lactose,as well as SCS(p<0.05).Therefore,the C6853T mutation of STAT5A gene could be used to evaluate the content of milk protein and lactose,as well as SCS in raw milk and dairy products.The content of milk protein ranged from 2.97%to 3.01%and the content of lactose ranged from 5.04%to 5.08%,SCS ranged from 2.61 to 2.95 when the milk samples with CC genotype.The content of milk protein ranged from 2.98%to 3.02%and the content of lactose ranged from 5.04%to 5.10%,SCS ranged from 2.68 to 3.02 when the milk samples with CT genotype.The content of milk protein ranged from 3.17%to 3.25%and the content of lactose ranged from 4.49%to 4.61%,SCS ranged from 1.39 to 1.83 when the milk samples with TT genotype.The genotype of the dairy products was determined to be CT genotype.The milk samples with TT genotype showed high milk protein and low lactose content and SCS,which was a very good choice for the production of high protein and low lactose dairy products.2.Evaluation method of fresh milk quality based on mutation of bovine CLU gene.The G15781A mutation on exon 7 of CLU gene was identified for genotyping,and the three genotypes of GG,GA and AA presented a significant correlation with the content of milk fat(p<0.05),and a slightly significant correlation with the content of lactose and total solids(p<0.05).Therefore,the G15781A mutation of CLU gene could be used to evaluate the content of milk fat,lactose and total solid.The content of milk fat ranged from 3.96%to 4.14%and the content of lactose ranged from 5.08%to 5.12%,the content of total solids ranged from 12.10%to 12.34%when the milk samples with GG genotype.The content of milk fat ranged from 3.91%to 4.27%and the content of lactose ranged from 4.89%to 5.03%,the content of total solids ranged from 12.25%to 13.07%when the milk samples with GA genotype.The content of milk fat ranged from 4.21%to 4.57%and the content of lactose ranged from 5.07%to 5.17%,the content of total solids ranged from 11.27%to 11.87%when the milk samples with AA genotype.The genotype of the dairy products was determined to be GA genotype.The milk samples with AA genotype were more in line with the acquisition of high quality fresh milk standards.3.Evaluation method of fresh milk quality based on mutation of bovine IGF2 gene.The G24507T mutation on exon 10 of IGF2 gene was identified for genotyping,and the three genotypes of GG,GT and TT presented a significant correlation with the content of milk protein(p<0.05).Therefore,the G24507T mutation of IGF2 gene could be used to evaluate the content of protein.The content of milk protein ranged from 2.96%to 3.00%when the milk samples with GG genotype.The content of milk protein ranged from 2.97%to 3.01%when the milk samples with GT genotype.The content of milk protein ranged from 3.24%to 3.34%when the milk samples with TT genotype.In terms of the content of milk protein,milk samples with TT genotype was higher than that with GG and GT,and producers tend to choose the milk samples with TT genotype to produce high quality dairy products.4.Evaluation method of fresh milk quality based on mutation of bovine BAF60c gene.The molecular characterization of bovine BAF60c gene was carried out,and found that the relative expression level of BAF60c gene in various tissues from high to low in turn were rumen,spleen,petalstomach,lung,kidney,testicle,back fat,reticulum,heart,liver,small intestine,caecum,longissimus dorsi,hind leg muscle,large intestine,front leg muscle and testicles.The T6060C mutation on intron 4 of BAF60c gene was identified for genotyping,and the three genotypes of CC,CT and TT presented a significant correlation with the content of lactose,and a slightly significant correlation with milk protein and fat-protein ratio(p<0.05).Therefore,the T6060C mutation of BAF60c gene could be used to evaluate the content of lactose and milk protein,as well as fat-protein ratio.The content of lactose ranged from 5.02%to 5.06%,the content of milk protein ranged from 2.98%to 3.02%and the fat-protein ratio ranged from 1.37 to 1.41 when the milk samples with TT genotype.The content of lactose ranged from 5.00%to 5.06%,the content of milk protein ranged from 2.84%to 2.90%and the fat-protein ratio ranged from 1.28 to 1.36 when the milk samples with TC genotype.The content of lactose ranged from 5.22%to 5.32%,the content of milk protein ranged from 3.22%to 3.32%and the fat-protein ratio ranged from 1.42 to 1.50 when the milk samples with CC genotype.The milk samples with CC genotype showed a higher content of lactose and milk protein,as well as fat-protein ratio than that with TT genotype and TC genotype,and producers tend to choose the milk samples with CC genotype to produce high quality dairy products.