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

The rate of hydrolysis of beta-lactoglobulin (genetic variant B) by trypsin in aqueous solution at pH of 7.6 and ionic strength 0.08 M (NaCl) at 25.0 degreesC increased with increasing hydrostatic pressure. At constant pressure (ambient, 100,150 and 250 MPa studied), the initial rate of disappearance of beta-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 k(c) and Michaelis constant K-m,) increased by a factor of 101 at 256 MPa compared with ambient pressure. While k(c) increased only for pressures up to 100 MPa, corresponding to an initial pressure-melted state (factor of 10(2) up to 100 MPa) with no further increase at higher pressure, K-m continuously decreased up to 250 MPa, corresponding to a binding volume of -37 ml mol(-1) of beta-lactoglobulin to trypsin. Thus, the enhanced digestibility of beta-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. (C) 2002 Elsevier Science Ltd. All rights reserved.