Whey protein fractionation: Isoelectric precipitation of α‐lactalbumin under gentle heat treatment

Abstract

The selective precipitation of α-lactalbumin (α-LA) at a pH around its isoelectric point (4.2) under heat treatment is the basis for a fractionation process of whey proteins. In these conditions, β-lactoglobulin remains soluble, whereas bovine serum albumin and immunoglobulins co-precipitate. Knowledge of the mechanism governing the α-LA precipitation influences the choice of operating conditions and enables optimization of the fractionation process. α-LA is a calcium metallo-protein and its isoelectric precipitation is governed by the protein-calcium complexation equilibrium. Citrate, a sequestrant of calcium, decreases the free calcium concentration and displaces the precipitation phenomenon to a lower temperature range. A study of the effect of citrate on the precipitation phenomena of whey proteins is presented. Whatever the citrate content, precipitation curves for bovine serum albumin (BSA) and α-LA intersect at a temperature around 45°C. For a temperature of heat treatment lower than 40°C, a selective enrichment in α-LA of the precipitated phase is observed. As addition of citrate leads to high α-LA precipitated fractions at a temperature around 35°C, the precipitation step may be performed at this temperature. It results in a reduced heat denaturation of whey proteins and in a higher α-LA purity in the precipitated fraction. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 391–397, 1997.