Single, combined, or sequential action of pressure and temperature on lipoxygenase in green beans (Phaseolus vulgaris L.): a kinetic inactivation study.

The objective of this investigation was to study kinetically the effect of pressure and temperature either as a single, as a combined, or as a sequential action on lipoxygenase (LOX) inactivation in crude green beans extract. The LOX isozymes in green beans extract had a different heat sensitivity but a similar pressure stability: two fractions following apparent first-order reactions, i.e., a heat-labile fraction and a heat-stable fraction, were observed in studies on its thermostability, whereas only one fraction following a first-order reaction was noticed in studies on its pressure stability. At ambient pressure, irreversible LOX inactivation was studied in a temperature range from 55 to 70 degrees C. At room temperature, pressures around 500 MPa were required in order to inactivate LOX in green beans extract. The effect of a pressure or a thermal pretreatment on LOX thermo- or barostability, respectively, was also investigated but no significant differences in inactivation kinetics due to the pretreatment were observed.