Effect of high hydrostatic pressure on the steady-state kinetics of tryptic hydrolysis of β-lactoglobulin

The rate of hydrolysis of β-lactoglobulin (genetic variant B) by trypsin in aqueous solution at pH of 7.6 and ionic strength 0.08 M (NaC1) at 25.0 °C increased with increasing hydrostatic pressure. At constant pressure (ambient, 100, 150 and 250 MPa studied), the initial rate of disappearance of β-lactoglobulin B could be analyzed using Michaelis–Menten kinetics (five initial substrate concentrations ranging from 0.11 to 0.88 mM used at each pressure). The over-all catalytic efficiency (ratio between catalytic constant kc and Michaelis constant Km) increased by a factor of 103 at 250 MPa compared with ambient pressure. While kc increased only for pressures up to 100 MPa, corresponding to an initial pressure-melted state (factor of 102 up to 100 MPa) with no further increase at higher pressure, Km continuously decreased up to 250 MPa, corresponding to a binding volume of −37 ml mol−1 of β-lactoglobulin to trypsin. Thus, the enhanced digestibility of β-lactoglobulin at elevated pressure is the result of a volume decrease during the association process and a volume decrease during the catalytic step. Pressure treatment of whey concentrates should be considered as an alternative processing technology for reduction of allergenicity of whey products.