Proteolysis of αs1-Casein by Papain in a Complex Environment. Influence of Ionic Strength on the Reaction Products

The influence of NaCl on bovine αs1-casein (αs1-CN) hydrolysis by papain (EC 3.4.22.2) was studied at pH 6.5 and 40°C. The electrophoretic analysis in presence of sodium dodecyl sulfate (SDS), showed that αs1-CN was sequentially hydrolyzed as the reaction time increased. The analysis by isoelectric focusing electrophoresis showed that after 1 min, the resulting peptides had their isoelectric point (pl) assessed between 4 and 9. With the increase of NaCl concentration, two peptides of apparent pl near pH 5 and 8.5 were progressively liberated. The chromatographic analysis by reverse phase HPLC showed that a major peak, observed after 1 min of reaction, persisted in the hydrolysates obtained in the presence of salt at all reaction times. It was concluded by the peptidic sequence determination that the hydrophobic C-terminal region of αs1-CN was not hydrolyzed in the presence of NaCl.