LIPID AUTOXIDATION IN RICE

Abstract

ABSTRACTWhen stored at room temperature in the dark, neither peroxide nor total carbonyls rose in raw lightly‐milled rice during 3 yr but parboiled rice became rancid in a few months. The rate of autoxidation was greatly increased when the samples were stored in thin layers in open dishes at a high temperature, but the effect of temperature was greater in raw rice than in parboiled rice. Exposure to light hastened the autoxidation in raw rice at room temperature; it had relatively less effect in parboiled rice or at a high temperature. A high (normal) moisture content delayed the onset of oxidation in lightly‐milled parboiled rice and delayed as well as suppressed it in raw rice, and vice versa. Surprisingly powdered raw rice autoxidized nearly as fast and as much as parboiled whole rice; but in parboiled rice grinding had only a moderate effect. The degree of milling had a dramatic effect on the autoxidation process in raw rice: unmilled rice was very stable, but the rate of oxidation increased sharply with increasing milling. In contrast, the degree of milling had little effect in parboiled rice. The reported presence of antioxidants in raw rice and their destruction in parboiled rice as well as the changed disposition of fat in the latter seem to be implicated with these results.