Selective Precipitation of Whey Proteins with Carboxymethylcellulose

Abstract

Anionic hydrocolloids undergo pH-dependent interactions with whey proteins. A partial fractionation of carboxymethylcellulose/protein complexes was achieved by selected conditions of pH, ionic strength, and ratio of carboxymethylcellulose to protein. A rapid screening method determined the amount of carboxymethylcellulose required. β-Lactoglobulin and bovine serum albumin were complexed at, pH 4 by adding a predetermined amount of carboxymethylcellulose solution to whey, cooling the mixture to 2C and collecting the precipitate by centrifugation (yield : 5.1 g/liter, CMC/protein ratio : 0.28). A second complex containing α-lactalbumin was precipitated by adjusting the supernatant to pH 3.2 and adding a controlled amount of carboxymethylcellulose at 2C (yield: 0.7 g/liter of remaining supernatant, CMC/protein ratio : 0.48). After removal of this complex by centrifugation the supernatant was adjusted to pH 7.5 which coprecipitated proteins (apparently proteose-peptones) along with calcium phosphate salts (yield of freeze-dried, dialyzed product: 0.1 g/liter, CMC/protein ratio: 0.05). With a combination of CMC treatment of whey at pH 4.0 and ammonium sulfate precipitation at pH 6.6, α-lactalbumin and immunoglobulins were recovered free of carboxyrnethylcellulose.