Vitamin E oxidation and tocopheroxyl radical stabilization in bleached rice bran oil

•Bleaching results in a change in the type of free radical in rice bran oil.•This new radical has an identical EPR spectrum to that of oxidized α-tocopherol.•This radical has unusually high stability in bleached rice bran oil.

Changes in the free radical components of rice bran oil before and after bleaching using a modified kaolin were investigated by electron paramagnetic resonance (EPR) spectroscopy. Before bleaching the EPR spectrum of the oil consisted of a single weak peak with g-value and linewidth similar to those of melanoidins, common colored components of seeds and husks. After bleaching, this was replaced by an EPR spectrum with 1H hyperfine structure characteristic of the α-tocopheroxyl radical, thus indicating some vitamin E oxidation during the bleaching process. This radical was exceptionally stable compared to its half-life in biological or simple chemical systems. The high stability of the α-tocopheroxyl radical indicates that reactions in the bleached oil are extremely slow, and that this oil has exceptional stability properties.