A hepatonephro-protective phenolic-rich extract from red onion (Allium cepa L.) peels

Onion peel is a common bio-waste, occasionally used in traditional medicine in treatment of liver ailment and inflammation. However, a phytochemical and biological study is further required to provide the scientific evidence for this use. A phenolic-rich extract of red onion peels (coded as ACPE) was primarily prepared and then subjected to chromatographic separation. From the extract, six phenolic antioxidant compounds along with two phytosterols were isolated and identified by means of spectroscopic (NMR and MS) analyses. The in vivo protective activity of the ACPE against the oxidative stress induced by carbon tetrachloride (CCl4) free radicals, in liver and kidney, was assessed in rats. Relative to the CCl4-challenged animals, pre-treatment with ACPE could significantly ameliorate the hepatonephro-linked serum and tissue markers in a dose-dependent response. The flavonol- and phenolic acid-based nature of constituents, the high phenolic content (72.33 +/- 5.30 mg gallic acid equivalent per one gram) and the significant antioxidant capacity (> 1/3 potency of rutin) of ACPE may be thus attributed strongly to the hepatonephro-protective and anti-inflammatory effect of ACPE. The results suggest that red onion peels can serve as a convenient and cost-effective source of high-value antioxidant nutraceuticals for protection against oxidative stress-related disorders.