Pressure-Aided Proteolysis of β-Casein

Beta-casein, which is present in the form of micelles at atmospheric pressure, has been hydrolyzed during pressure treatment to improve the accessibility of the protein. Two proteolytic enzymes with different specificities were used. Trypsin was aimed at mainly hydrolyzing hydrophilic segments of beta-casein and chymotrypsin at hydrolyzing hydrophobic segments of beta-casein. Measurements on aggregation during hydrolysis at atmospheric pressure showed that probably not micelle disruption, but disruption of much larger aggregates, occurs in the process. Peptide profiles were measured via reversed-phase chromatography. Measurements on enzyme activity after pressure treatments showed that trypsin was inactivated by pressure, which could explain all differences in peptide profiles compared to atmospheric experiments. Pressure did not influence the reaction mechanism, probably because the hydrophilic part of beta-casein is sufficiently accessible. However, chymotryptic proteolysis under pressure yielded new peptides that could not be explained by a change in enzyme activity. Here, pressure altered the mechanism of hydrolysis, by changing either enzyme specificity or substrate accessibility, which led to different peptides that can have different properties.