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

100\% methyl-, 59\% ethyl- and 56\% propyl-esters of beta -casein and 52\% methyl-, 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) was enhanced considerably after esterification. Methyl esters of both proteins yielded the highest levels of DH. Compared to SDS-PAGE of peptic hydrolysates 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 -lactalbumin showed the disappearance of the bands corresponding to peptides of low molecular weights. Compared with native protein, RP-HPLC profiles of peptic hydrolysates of esterified beta -casein showed more hydrophobic peptides. The major changes in RP-HPLC of peptic hydrolysates of esterified alpha -lactalbumin concerned peptides eluted between 20 and 30 min (hydrophobic), while the distribution of peptides eluted between 10 and 20 min (hydrophilic) remained constant.