INVITRO PROTEOLYSIS AND FUNCTIONAL-PROPERTIES OF REDUCTIVELY ALKYLATED BETA-CASEIN DERIVATIVES

Beta-casein amino groups were modified with aldehydes and dialdehydes via reductive alkylation at pH 8.0. The degree of alkylation was controlled by the amount of the alkylating reagent applied. The initial rates of alpha-chymotrypsin-catalysed hydrolysis of alkylated beta-casein were inversely related to the size of the modifying group. Proteolysis of modified beta-casein with trypsin (18 h) or with alpha-chymotrypsin (48 h) depended on the nature and size of the substituent applied. The measurements of tryptophan fluorescence indicate that the modifications also induced conformation change. Solubilities of methyl-, ethyl- or benzyl-beta-casein slightly increased; solubilities of beta-casein dialdehyde derivatives were significantly lower than that of native beta-casein. Emulsion stability of methyl- or ethyl-beta-casein was higher than that of native beta-casein in the acidic pH range. After modification with glyoxal, the emulsifying activity and the emulsion stability of beta-casein decreased. The emulsifying activity of benzyl-beta-casein was lower than that of native beta-casein. Phthalylated beta-casein displayed the poorest emulsion stability.