ELECTROPHORETIC MOBILITY OF CASEIN MICELLES

A simplified moving boundary electrophoresis technique was developed for the measurement of the electrophoretic mobility of casein micelles. The .zeta. potentials of casein micelles from different skim-milk samples were calculated using Henry''s equation and decrease with decrease in pH of 6.9-5.3 and increase with increase in temperature of 10-45.degree. C. Neither severe heat treatment (up to 135.degree. C for 51 min) nor centrifugal fractionation of micelles into different micelle size ranges had any significant effect on z potential. The ionic composition of the serum phase was extremely important in determining the electrophoretic mobility. Casein micelles electrophoresed through milk ultrafiltrate consistently gave lower mobilities than the same micelles centrifuged through milk centrifugate. The results are discussed in relation to present theories of casein micelle structure; these theories do not accommodate all of the observations.