Photochemical Changes in Major Whey Proteins of Cow's Milk

Catalytic photoaggregation and photodegradation of purified ~-lactalbumin, 3-1actoglobulin, and acid whey proteins isolated from homogenized milk were studied. Disc gel electrophoresis of fluorescent light-and sunlight-exposed c~-lactalbumin resulted in the formation of high molecular weight protein fractions with a corresponding decrease in the major protein band. When 3-1actoglobulin was treated and analyzed similarly, high molecular weight proteins appeared with a concurrent decrease in the major band. Light-exposed whey had diminished intensities in all the bands. Riboflavin was necessary to catalyze the photochemical changes in the proteins. Gel filtration chromatography with Sephadex G-75 of purified protein samples and acid whey demonstrated an increase in a high molecular fraction indicating aggregation of protein following exposure. Lowry assay of exposed protein fractions confirmed photoaggregation, and N-group analysis provided supporting evidence of peptide bond hydrolysis.