Identification of oxidative processes during simulated mastication of uncooked foods using electron paramagnetic resonance spectroscopy

Abstract

Electron paramagnetic resonance (EPR) spectroscopy is used to measure directly the generation of free radicals during a simulation of the mastication process. This involves the gentle grinding of the food product in the presence of a spin trap, a molecule which reacts selectively with unstable free radicals to generate (more) stable radical adducts, which can then be characterised. With mushrooms of the Agaricus family, adducts consistent with a carbon-centred radical are seen with a wide range of spin traps and this radical has been confirmed as 4-(hydroxymethyl)phenyl. In plant tissues that are rich in ascorbic acid, this molecule competes successfully with spin traps for the free radicals and the (monodehydro)ascorbate radical, formed by the 1-electron oxidation of ascorbic acid, is seen in the EPR spectra. However, with >50% of the plant tissue samples studied in the present experiment, free radicals resulting from oxidation of the spin traps were observed. The formation of such molecules, for which oxygen was found to be necessary, requires the existence of powerful oxidation processes as the plant tissue is broken down. Such pro-oxidant behaviour is contrary to the popular assumption that the beneficial effects of uncooked plant tissues are the result of their high levels of anti-oxidant molecules.