Limited Proteolysis of α-Lactalbumin and Whey Protein Isolate: Effect on Their Functional Properties

Millions of tons of whey proteins are produced each year from cows' milk during manufacture of soft and hard cheeses. Some of the whey containing these proteins (β-lactoglobulin, α-lactalbumin, serum albumin, lactoferrin, etc.) is fed to animals, some is discarded and more and more is being used as protein concentrates and isolates in human food. These proteins are relatively soluble except near the isoelectric point (pI) of the proteins, namely pH 4-6. A number of foods, such as fruit juices and vegetable products, have pHs in this same pH region, thereby limiting use of the whey proteins. Perhaps limited proteolysis (1-5%) and/or chemical modifications will increase their solubility, especially near the pI, and may increase their foaming capacity and stability and/or emulsifying activity index and stability. We have shown previously that limited proteolysis (1) and phosphorylation (2) improve the functional properties of β-lactoglobulin. We report here the effect of limited proteolysis on the functional properties of purified á-lactalbumin and of whey protein isolate from pH 2 to 10 by endoproteinases Glu-C, Lys-C, Arg-C and trypsin.