Electrophoresis of Cottage Cheese Whey Proteins and Their Polymers

Abstract

Cottage cheese whey solutions containing sodium dodecyl sulfate were resolved electrophoretically on 5% sodium dodecyl sulfate polyacrylamide gels. Major bands were identified by comparing their electrophoretic mobilities to those of known whey components. Other components were identified principally from molecular weights determined from a calibration correlating mobility and molecular weight. Conditions which affect polymerization of proteins were studied in whey and solutions of purified beta-lactoglobulin. Formation of a number of polymers was induced by concentrating the whey samples, lowering the temperature, adjusting pH, or adding salts. The dimer, trimer, tetramer, and octamer of beta-lactoglobulin, the dimer and trimer of bovine serum albumin, and several unidentified components in the 100,000 to 300,000 molecular weight range were observed. The octamer state of beta-lactoglobulin was observed in whey at pH values between 5.1 and 8.0, at temperatures below 10 C, and with .2M addition of potassium thiocyanate, potassium iodide, calcium chloride, or sodium acetate. Similar polymer formation, and temperature and pH effects, were observed with solutions of purified beta-lactoglobulin, which contained dimers, trimers, and tetramers. The beta-lactoglobulin octamer in whey samples could be dissociated by the addition of acid. The bovine serum albumin dimer appeared in whey at pH above 6.2 and at -minus 1 C.