Alterations in polyunsaturated fatty acid composition of Voandzeia subterranea seeds upon .gamma. irradiation

Exposure of V. subterranea seeds, a herbaceous plant from Madagascar belonging to the family of legumes, to gamma irradiation resulted in a polyunsaturated fatty acids decrease associated with the formation of UV-absorbing substances. The finding that products containing conjugated diene structure are formed during lipid extract irradiation indicates that hydroperoxy fatty acids may arise not only by enzymatic reactions but also by nonenzymatic oxygenation of polyunsaturated fatty acids promoted by ionizing radiation. Dehulled green seeds, flour made from dehulled green seeds, and lipid extract were studied for irradiation dose dependent changes in fatty acids compositions and hydroperoxydiene synthesis. The irradiation dose is more efficient in lipid extract than in dehulled green seeds or in flour made from these seeds, suggesting that the formation of UV-absorbing products is not a reliable clue for enzyme activity owing to the absence of protein in lipid extract. A homolytic pathway for the biogenesis of hydroperoxy fatty acids from polyunsaturated fatty acids is proposed. This involves an initiating radical which promotes a chain mechanism in which the O2 adsorbed is converted to hydroperoxide. Conclusively, preservation of fatty acid oxygenation should be a primary goal in the ionizing radiation processes of V. subterranea seeds and generally in the preservation of food of plant origin by ionizing radiation.