Study On Micellar Structure And Monomer Separation Process Of Yak Casein

The yak casein micelle structure is the core of the whole process of yak milk products.However,most of the reports ofyak milk focused on the changes in the properties of yak casein under different treatment conditions.There are few of reports on the structural changes ofyak casein during processing processing.Meanwhile,with the recognition of the value of casein monomer,its application is gradually extensive.However,the current separation level of casein monomer is far from the requirement of industrial application,and the waste of raw materials is very serious.To explore the structure of the yak casein micelles and the changes in their processing,andfind a suitableprocess for the separation of casein monomer the structure of yak casein micelles was studied under different pH and the separation process of casein monomers was optimized.In this research,the yak skim was adjusted to different pH,the contents of main ions and monomer contents dissociated from micelleswere determined.The stability,micelle size and fluorescence spectrum changes after pH treatment were measured,and the morphology and internal structure were observed.The chemical composition and structure of yak casein micelles were analyzed.In addition,the process for casein monomers'separation were obtained,which could gain?_s-casein,?-casein,?-caseinsimultaneous by ion exchange column.The structure and the different properties of some monomers were studied.The results of the study showed that:1.At natural pH,12.2%?-CN,13.7%?_s-CN and 13.8%?-CN in yak milk exist in a free form.The Ca and P were related to the formation of casein micelles and contribute to the stablility of casein micelle structure at pH 6.8.2.In pH 6.8~8.2,with the increase of pH,micelles became loose until the occurrence of dissociation,while the steric hindrance effect was reduced.In pH 6.35~6.80,with the increase of acidification degree,colloidal calcium phosphate dissolved but casein monomers did not aggregate,because micelle was positively charged.In pH 4.6~6.35,the colloidal calcium phosphate continued to dissolve,and the casein monomer gradually aggregated until precipitated.In pH?4.6,the precipitation of casein could dissolve.3.The optimum separation process of casein monomer showed that the sample mass was2g(resin mass 100g);the optimum amount of mixed eluent was 80 m L;and the optimum the gradient of B buffer solution was7.50%.In this process,?-CN was the first casein to be elused,the highest purity could reach 94.00%and the recovery rate was 70.24%.The second casein was?-CN,which purity could reach 89.08%with a recovery rate of 59.52%.The last was?_s-CN,purity was up to 95.20%with a recovery rate of 40.20%.The total recovery was61.84%.4.In terms of functional properties,the foaming property,foam stability and hydroscopicity of?-CN are the topmost,the foaming property of?_s-CN is the lowermost,but the emulsifying property of?_s-CN is the highest.The emulsification and hydroscopicity of?-CN are the worst,but the oil absorption is the best.The emulsifying stability of CN is the highest,but the oil absorption is the worst.The foaming property,foam stability,hydroscopicity and emulsifying property of CN are between monomers.The amino acid sequence of the?-CN of yak milk was different at the 175th amino acid from the bovine?-CN.The difference of?_s-CN at 30th,103th,104th sites.