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Photochemical Changes in Major Whey Proteins of Cow's Milk¹

Food Science Department, The Pennsylvania State University, University Park 16802

ABSTRACT

Catalytic photoaggregation and photodegradation of purified -lactalbumin, ß-lactoglobulin, and acid whey proteins isolated from homogenized milk were studied. Disc gel electrophoresis of fluorescent light- and sunlight-exposed -lactalbumin resulted in the formation of high molecular weight protein fractions with a corresponding decrease in the major protein band. When ß-lactoglobulin 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.

¹ Authorized for Publication on July 29, 1977, as Paper No. 5346 in the Journal Series of the Pennsylvania Agricultural Experiment Station.

² Dept. of Dairy Science, South Dakota State University, Brookings 57006