Rapid Separation and Quantification of Major Caseins and Whey Proteins of Bovine Milk by Polyacrylamide Gel Electrophoresis

Abstract

A rapid polyacrylamide gel electro- phoretic method was developed for separating and quantifying major pro- teins in casein and whey protein fractions of bovine milk. For casein separation, best results were achieved by an 8% poly- acrylamide gel containing 4 M urea and a top layer of large pore sample gel; for whey protein the most_ satisfactory separation was with 12% polyacrylamide gel in the absence of urea and a large pore gel. Electrophoretic conditions for separa- tion of whey protein were also applicable for identifying genetic variants of /3- lactoglobulin. Densitometric tracings were used to resolve and quantify protein peaks from stained bands in the gels. Casein was resolved into three major frac- tions with relative proportions of 50:30: 15 for as1- and oq2-casein, /3-casein, and K-casein. Whey protein was resolved into four major fractions with relative propor- tions of approximately 60:20:7:13 for /3-1actoglobulin, aqactalbumin, serum al- bumin, and immunoglobulin.