B. Lieske et G. Konrad, INTERRELATION BETWEEN PH AND AVAILABILITY OF ALPHA-LACTALBUMIN AND BETA-LACTOGLOBULIN FOR PROTEOLYSIS BY PAPAIN, International dairy journal, 6(4), 1996, pp. 359-370
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