An Electrophoretic Study of the Protein in Skimmilk

Abstract

Summary Electrophoretic studies of unfractionated and unheated skimmilk proteins at ionic strengths of 0.02, 0.1 and 0.5 at pH's 8.4, 6.6, 5.4, 4.1 and 3.2 have shown that: (a)The electrophoretie mobilities of the proteins in unfractionated skimmilk are appreciably lower than the mobilities of the corresponding isolated proteins. (b)The isoelectric points of the proteins in unfractionated skimmilk are approximately the same as the isoelectric points of the corresponding isolated proteins reported by other workers. (c)The best electrophoretic resolution of the proteins in skimmilk occurs at pH 6.6 and ionic strengths of 0.02 and 0.1. (d)α-Casein migrates as two distinct components, α 1 - and α 2 -casein, over a range of pH's above 4.2 at ionic strengths of 0.02 and 0.10. (e)An interaction occurs between the α- and β-casein components of skimmilk which increases in degrees as pH is lowered from 8.4 to 5.4 at ionic strength 0.02. Heat treatments of skimmilk for 30 min. at 65, 75 and 85 C. were found to cause the following changes in the electrophoretic properties of the protein components as revealed by electrophoresis measurements at pH 6.6, r/2 = 0.1: (a) The mobilities of α -casein, β -casein and β -lactoglobulin are lowered by heating, the effect being greater at the higher temperatures; (b) The concentrations of β -lactoglobulin and β -casein are decreased and the concentration of protein migrating with a-casein is increased by heating skimmilk under the conditions given.