Effect Of Milk Protein Polymorphism And Milk Composition On Milk Coagulation Property Of Cow Milk

According to the investigation,in the early processing of milk cheese,there is non-coagulation phenomenon,which will seriously affect the product quality.In view of this phenomenon,this study analyzed the reasons of non-coagulation of milk produced by Holstein cows in China.The different types of milk were analyzed,the blood samples of1071 Holstein cows were collected,and the genotype polymorphisms of ?-CN and ?-LG were analyzed by combining PCR amplification and sequencing.Milk samples were collected to evaluate the ability of milk curd.on the basis of preliminary screening,we selected the samples with good coagulation(WC),poor coagulation(PC)and non-coagulation(NC).We compared and analyzed the milk protein genotype,milk composition analysis,physicochemical properties,ion distribution,rheological properties,milk protein polymorphism and so on.The findings are as follows:1.By detecting the ?-LG and ?-CN genotyping in the samples of dairy cows,Showing?-LG three genotypes(AA?AB and BB),?-CN have six genotypes(AA?AB?AE?BB?BE and EE).And there were significant differences in the milk coagulation frequency between casein and lactoglobulin,there were 4%?8% milk without coagulating.The highest proportion of cows secreting milk from ?-CN AB and ?-LG AB genotypes,39.70% and 48.48%,respectively.The ?-LG genotype was AA,more suitable for processing cheese;and it was found that ?-CN BB genotypes of milk had better curd performance,E alleles have a stronger effect on coagulation time than A alleles.The genotype had little effect on the ion content and distribution in milk,no significant difference was detected,but as can be seen in different genotypes of milk,the difference in protein content is obvious,it has a significant effect on the ability of coagulation.2.Processed three types of coagulation milk samples,the dynamic rheological analysis,composition and physical and chemical properties of milk were measured by rheometer.Data show that WC samples form a state of compactness in a short period of time(11 min),the gel structure is stable(G',139.35 Pa),PC and NC samples,significant differences in time and gel strength.The contents of casein and calcium ions in the samples with good coagulant properties were higher,the higher the total colloidal calcium phosphate,the better for the enzyme gel,p H values affect MCP changes.Higher relative concentration of whey protein in milk has adverse effects on enzyme coagulation,instead,?-CN the higher the relative content,the better the coagulation performance.Casein micelle size is inversely proportional to the coagulation performance of milk.The change of soluble salt and the activity of calcium ion and the dissolution of colloidal calcium phosphate will affect the coagulation effect of milk.3.The protein type and relative content in milk were detected by the separation and purification of milk protein.The results showed that the protein content of ?-CN and ?-CN was higher than that of PC and NC samples;the milk contained many forms of protein,such as phosphorylation,in NC and PC samples,which affected the coagulation performance of milk;the relative protein content of milk was quantified.The results showed that the ?-CN content(10.38%)in milk was the highest and the significant difference was significant(p<0.05).Moreover,the content of other proteins in NC?PC samples is relatively low,which proves that the protein content has a significant effect on milk properties,especially the ?-CN content,which is positively correlated with the properties of coagulation.To sum up,genotype polymorphism,milk protein polymorphism and content,as well as milk composition differences,will affect milk coagulation property.