INTERRELATION BETWEEN PH AND AVAILABILITY OF ALPHA-LACTALBUMIN AND BETA-LACTOGLOBULIN FOR PROTEOLYSIS BY PAPAIN

The enzymic hydrolysis of alpha-lactalbumin and beta-lactoglobulin by papain was studied on pure whey protein fractions and on a commercial whey protein concentrate (Lacprodan 80). The effect of pH on substrate specificity of papain was indicated by the increase in proteolytic fr agments as free alpha-amino nitrogen, by the decrease in proteinaceous matter using the BIO-RAD protein assay, by gel permeation chromatogra phy (Sephadex G-100) and FPLC anion-exchange chromatography. Enzymic a vailability of beta-lactoglobulin was determined in view of its pH-dep endent molecular association status and was best at pH > 7.5 favouring the monomeric structure, whereas alpha-lactalbumin was hydrolysed wit hout limitation only at acidic pH. The binding of calcium protected co mpletely native alpha-lactalbumin against proteolytic degradation at p H 6.0 and 8.0. This protective effect was lower for alpha-lactalbumin in the commercial whey protein concentrate and was absent in calcium-d epleted alpha-lactalbumin. (C) Elsevier Science Ltd