The stability of almond β-glucosidase during combined high pressure-thermal processing: a kinetic study

The thermal and the combined high pressure-thermal inactivation kinetics of almond beta-glucosidase (beta-d-glucoside glucohydrolase, EC 3.2.1.21) were investigated at pressures from 0.1 to 600 MPa and temperatures ranging from 30 to 80 A degrees C. Thermal treatments at temperatures higher than 50 A degrees C resulted in significant inactivation with complete inactivation after 2 min of treatment at 80 A degrees C. Both the thermal and high pressure inactivation kinetics were described well by first-order model. Application of pressure increased the inactivation kinetics of the enzyme except at moderate temperatures (50 to 70 A degrees C) and pressures between 0.1 and 100 MPa where slight pressure stabilisation of the enzyme against thermal denaturation was observed. The activation energy for the inactivation of the enzyme at atmospheric pressure was estimated to be 216.2 A +/- 8.6 kJ/mol decreasing to 55.2 A +/- 3.9 kJ/mol at 600 MPa. The activation volumes were negative at all temperature conditions excluding the temperature-pressure range where slight pressure stabilisation was observed. The values of the activation volumes were estimated to be -29.6 A +/- 0.6, -29.8 A +/- 1.7, -20.6 A +/- 3.2, -41.2 A +/- 4.8, -36.5 A +/- 1.8, -39.6 A +/- 4.3, -31.0 A +/- 4.5 and -33.8 A +/- 3.9 cm(3)/mol at 30, 35, 40, 45, 50, 60, 65 and 70 A degrees C, respectively, with no clear trend with temperature. The pressure-temperature dependence of the inactivation rate constants was well described by an empirical third-order polynomial model.