OPTIMIZATION OF A WHEY-PROTEIN FRACTIONATION PROCESS-BASED ON THE SELECTIVE PRECIPITATION OF ALPHA-LACTALBUMIN

Whey protein fractionation based on the selective isoelectric precipit ation of alpha-lactalbumin has been optimised by an overall approach. Precipitation phenomena and rheological characteristics of the fluid a fter heat treatment have both been considered. Control of calcium conc entration, a new operating parameter, has optimised the precipitation step. A reduction of this concentration leads to an increase in the al pha-lactalbumin fraction precipitated at a moderate protein concentrat ion. 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 bo vine serum albumin has been studied. However, there are no conditions under which alpha-lactalbumin is the only protein that precipitates. T o separate precipitated and soluble fractions, centrifugation is the m ethod proposed, as it is more efficient than microfiltration. After so lubilisation, the two forms of alpha-lactalbumin may be recovered: the apo-alpha-lactalbumin with a calcium-free solvent, and the native for m with a calcium solvent. When a solution of calcium chloride is used, solubilisation is a fractionation step (increase of 23% in alpha-LA p urity), as the immunoglobulins remain insoluble.