Onion flesh and onion peel enhance antioxidant status in aged rats

This study was designed to investigate the effects of dietary onion flesh or onion peel on lipid peroxides and DNA damage in aged rats. Sprague Dawley male rats (n=40, 16 mo old) were blocked into five groups and raised for 3 mo with either an onion-free control diet or onion diets (Allium cepa L., intermediate-day variety) containing either 5% (w/w) powdered dried onion flesh, 5% (w/w) powdered dried onion peel or ethanol extracts of the two powdered forms of onion. Total antioxidant status (TAS) and levels of total polyphenols and quercetin were greatest in onion peel ethanol extract, followed by onion peel powder, onion flesh ethanol extract, and onion flesh powder. Plasma quercetin and isorhamnetin levels were markedly increased by onion peel powder and onion peel ethanol extract. Rats fed onion flesh powder or onion peel powder had a higher plasma TAS than rats fed the control diet. Onion peel powder reduced liver thiobarbituric reactive substances relative to those of the control diet in aged rats (p<0.05). Brain 8-isoprostane levels were markedly decreased by all four onion diets and the decrease was significant for the onion flesh powder and onion peel powder diets (p<0.05). There was no significant decrease in cellular DNA damage in the kidney or brain tissue among rats fed the four onion diets. Onion flesh or onion peel enhanced antioxidant status in aged rats and may be beneficial for the elderly as a means of lowering lipid peroxide levels.