Oxidative stress related to the aging process can increase the risk of degenerative disease. Red onions contain antioxidative compounds. This study was designed to investigate the effect of dietary red onion peel and/or flesh on antioxidative activity in rats. Twenty Sprague-Dawley male rats (18 weeks old) were divided into four groups. Each group was raised for 4 weeks on a red onion free control diet (ND), red onion diet containing 5% red onion peel (RP), 5% red onion flesh (RF), or 5% red onion peel+flesh (RPF). The results demonstrated that serum SOD activity was significantly increased in the RP and RPF groups, whereas glutathione peroxidase (GPx) activity was significantly higher in the RF group than in the ND group. Catalase activity and ORAC activity in liver showed upward tendency in the RP, RF, and RPF groups although the differences were not statistically significant. Liver malondialdehyde levels in the RPF group were significantly lower than those in the ND group were. In conclusion, red onion may enhance antioxidant defense mechanism through the induction of plasma SOD and GPx activities and inhibited liver lipid peroxidation. Therefore, red onion may exert important protective effects against oxidative stress related diseases.
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