Optimisation of a whey protein fractionation process based on the selective precipitation of alpha-lactalbumin

Whey protein fractionation based on the selective isoelectric precipitation of alpha-lactalbumin has been optimised by an overall approach. Precipitation phenomena and rheological characteristics of the fluid after heat treatment have both been considered. Control of calcium concentration, a new operating parameter, has optimised the precipitation step. A reduction of this concentration leads to an increase in the alpha-lactalbumin fraction precipitated at a moderate protein concentration. The use of citric acid, a calcium complexation agent, is proposed. It permits simultaneous adjustment of the pH and a reduction in the free calcium concentration. Co-precipitation of immunoglobulins and bovine serum albumin has been studied. However, there are no conditions under which alpha-lactalbumin is the only protein that precipitates. To separate precipitated and soluble fractions, centrifugation is the method proposed, as it is more efficient than microfiltration. After solubilisation, the two forms of alpha-lactalbumin may be recovered: the apo-alpha-lactalbumin with a calcium-free solvent, and the native form with a calcium solvent. When a solution of calcium chloride is used, solubilisation is a fractionation step (increase of 23% in alpha-LA purity), as the immunoglobulins remain insoluble.