Peptic hydrolysis of methyl-, ethyl-, and propyl-esters of beta-casein andalpha-lactalbumin

100% methyl-, 59% ethyl- and 56% propyl-esters of beta -casein and 52% meth yl-, 36% ethyl- and 25% propyl-esters of alpha -lactalbumin were prepared. Ester groups were 100% stable during 24 h incubation with pepsin or citric acid buffer at pH 2.6 and 37 degreesC. The degree of pepsinolysis (% DH) wa s enhanced considerably after esterification. Methyl esters of both protein s yielded the highest levels of DH. Compared to SDS-PAGE of peptic hydrolys ates of native proteins, those of esterified beta -caseins demonstrated the disappearance of the bands corresponding to peptides of medium and of high molecular weights; SDS-PAGE of peptic hydrolysates of esterified alpha -la ctalbumin showed the disappearance of the bands corresponding to peptides o f low molecular weights. Compared with native protein, RP-HPLC profiles of peptic hydrolysates of esterified beta -casein showed more hydrophobic pept ides. The major changes in RP-HPLC of peptic hydrolysates of esterified alp ha -lactalbumin concerned peptides eluted between 20 and 30 min (hydrophobi c), while the distribution of peptides eluted between 10 and 20 min (hydrop hilic) remained constant.