Quantitation of Caseins and Whey Proteins of Processed Milks and Whey Protein Concentrates, Application of Gel Electrophoresis, and Comparison with Harland-Ashworth Procedure

Abstract

Alternate methods for quantitation of caseins and whey proteins in milk products were investigated. The Harland-Ashworth and Leighton procedures, which are used for routine determinations of soluble whey proteins in milk, could not be adapted satisfactorily to quantitation of whey protein in blends of nonfat dry milk solids and whey protein concentrates because of problems of precipitation techniques. Gel electrophoresis in sodium dodecyl sulfate does not require fractionation prior to analysis and works well for nonfat dry milk solids, whey protein concentrates, and blends of these products, as well as total milk protein concentrates. Use of thiourea and hydrogen peroxide as gel catalysts improves band resolution and allows for easy handling and better quantitation. This method, which is an adaptation of the Laemmli procedure, may be of use for detecting adulteration of nonfat dry milk solids or even fluid milk with whey protein concentrates and may find other applications; 10 major milk proteins can be visualized and quantitated on one gel electrophoretogram.