Antioxidant and antimicrobial activities of the methanol extracts from pummelo (Citrus grandis Osbeck) fruit albedo tissues

The present study was conducted to evaluate the antioxidant and antimicrobial properties of methanol (100 and 80% aqueous) extracts of pummelo fruits albedo (Citrus grandis Osbeck). The antioxidant and antibacterial activity for crude extracts and isolated compounds were evaluated using free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) and Paper disc diffusion method. A 100% Methanol (MeOH) extract was steeped in water at different pH levels and partitioned with ethyl acetate (EtOAc) to give basic, acidic, neutral, and phenolic fractions. The neutral extract was found to possess maximum antioxidant and antibacterial activity. Thereafter, neutral extract was carried out on a silica gel column and eluted with hexane:EtOAc:acetone and preparative TLC (PTLC) to give oil buntan compound, linoleic acid methyl ester, β-sitosterol, sigmasterol, limonin, nomilin and meranzin hydrate were isolated. While, 80% MeOH extract was fractionated also using a silica gel column and PTLC to give isomeranzin hydrate, p-coumaric acid and caffeic acid compound. The extract concentration providing 50% inhibition (IC50) was as follows; oil buntan compound 95 μg/mL, caffeic acid 45 μg/mL, p-coumaric acid 105 μg/mL, limonin + nomilin (mixture) 135 μg/mL was lower than that of synthetic antioxidant butylated hydroxyanisole (BHA) 40 μg/mL. The inhibitory zone (mm) of bacteria tested was 2.9–4.1 mm caffeic acid and 11.6–15.1 mm p-coumaric acid.