Comparison of microwave, conventional and combination heat treatments on wheat germ lipase activity

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Abstract
Summary: Commercial wheat germ lipase inactivation was analysed at various temperatures with reference to conventional and microwave heating. A temperature controlled water‐bath was used for conventional heating. A custom designed microwave temperature control system was used to maintain test samples at selected temperatures either by full exposure to microwaves (microwave heating) or partial exposure by immersion in water (in a beaker) maintained at the desired temperature using the microwave oven (mixed mode). Lipase inactivation was analysed using first‐order kinetics resulting in activation energies (Ea) of 20.9, 25.4 and 18.7 kcal mole‐1 for the conventional, microwave and mixed mode heating, respectively. the activation energies of conventional and mixed mode heating were somewhat more comparable, while the microwave mode resulted in a slightly higher activation energy. the higher enzyme inactivation rate constants observed under microwave heating conditions were attributed to possible non‐thermal effects associated with microwave energy