Antioxidant activities of major components of γ‐oryzanol from rice bran using a linoleic acid model

The change in hydroperoxides of linoleic acid incubated with constant micro air flow at 37°C was used to evaluate the antioxidant activities of three major components of γ‐oryzanol from rice bran (cycloartenyl ferulate, 24‐methylene cycloartanyl ferulate, and campesteryl ferulate) compared with α‐tocopherol and ferulic acid. The four hydroperoxide isomers of linoleic acid, 9‐hydroperoxy‐10‐trans, 12‐cis‐octadecadienoic acid [9HPODE(t,c)], 9‐hydroperoxy‐10‐trans, 12‐trans‐octadecadienoic acid, 13‐hydroperoxy‐9‐cis, 11‐trans‐octadecadienoic acid [13HPODE(c,t)], and 13‐hydroperoxy‐9‐trans, 11‐trans‐octadecadienoic acid, were measured using normal‐phase high‐performance liquid chromatography with an ultraviolet detector. The three components of γ‐oryzanol evidenced significant antioxidant activity when they were mixed with linoleic acid in a molar ratio of 1∶100 and 1∶250 but not in a molar ratio of 1∶500 (P<0.05). α‐Tocopherol and ferulic acid also demonstrated significant antioxidant activity at all three molar ratios (P<0.05). The highest molar ratio (1∶100) of α‐tocopherol, however, caused greater levels of 9HPODE(t,c) and 13HPODE(c,t) than the other two less concentrated treatments.