THERMAL INACTIVATION OF PEA FLOUR LIPOXYGENASE

Lipoxygenase (LOX) was determined in pea flour (9.6% moisture) samples which had been exposed to 90-130-degrees-C for 5-45 min, and in crude aqueous extracts (5%; pH 6.7) of previously unheated pea flour which had been exposed to 40-80-degrees-C for 5-30 min. The rate of thermal inactivation of pea LOX was shown to follow first-order reaction kinetics. The rate constants, k(min-1), ranged from 0.005 to 0.252 for the flour, and from 0.068 to 0.267 (60-80-degrees-C) for the crude extract. The respective thermodynamic values were: for the energy of activation (E(a)), 126.2 and 64.6 kJmole-1; for the enthalpy of activation (DELTA-H double-ended-dagger), 123.1 and 61.8 kJmole-1; for the free energy of activation (DELTA-G double-ended-dagger), 118.0 and 101.4 kJmole-1. The greater thermostability of LOX in the pea flour under dry-heat conditions, and the observed differences in the E(a), DELTA-H double-ended-dagger and DELTA-S double-ended-dagger values, may be accounted for by its possible complexation with other macromolecules and by the structure of the water surrounding the native enzyme.