ELECTROPHORETIC SYSTEMS FOR THE FRACTIONAL COMPOSITION ANALYSIS OF PROTEINS IN MILK OF COWS OF DIFFERENT BREEDS

A comparative analysis of the fractional composition of the main milk proteins of the casein complex and whey from Holstein and Jersey cows from the farms in the Ternopil region of Ukraine was carried out in the work. The milk of these breeds differs in the qualitative and quantitative composition of protein fractions, which may be important for the production of certain types of products. Analysis of literature data showed that genetic variants of the main milk proteins primarily differ in charges and the ability to aggregate in solutions. Therefore, two electrophoretic systems were used to analyze protein fractions, which allow separating caseins and whey proteins according to their charges. These are polyacrylamide gel electrophoresis in the presence of urea for the analysis of caseins and express electrophoresis in native conditions for the analysis of whey proteins. Studies of skim milk samples from Holstein and Jersey breeds using two electrophoresis systems allowed the identification of only three main fractions: αS1-casein, β-casein and β-lactoglobulin (β-Lg). Identification of other fractions and quantitative assessment of all fractions is complicated by the overlapping of protein bands on electrophoregrams. Better results were obtained with separate analysis of caseins and whey proteins from milk of each breed. Analysis of caseins by electrophoresis in the presence of urea allowed to identify and establish the relative content of the following fractions in Holstein milk: αS1-CN B-8P (35,4±2,1%), αS2-CN A-XP (15,2±1,1%), β-CN A2-5P (36,2±1,6%), and in Jersey milk: αS1-CN C-8P (36,6±1,8%), αS2-CN A-XP (16,2±1,2%) and β-CN A2-5P (32,8±1,9%). Analysis of whey samples by express electrophoresis in native conditions showed the presence of two genetic variants of β-Lg, but in different ratios – in milk of Holstein cows: β-Lg A (16,7±1,3%) and β-Lg B (23,7±2,2%), and in milk of Jersey cows: β-Lg A (14,9±1,5%) and β-Lg B (27,4±2,3%). The results of express electrophoresis also showed that the same variant α-La – α-La B is present in both milk samples.