Phenolic Content and in vitro Antioxidant Activities of Sweet Orange (Citrus sinensis L.) Fruit Wastes

Abstract

The phenolic contents and in vitro antioxidant activities of waste components (flavedo, albedo and seed) obtained from Citrus sinensis (orange) fruit were evaluated in this study. Two extracts (ethanol and hydroethanol) were prepared from each sweet orange component. Total phenolic contents were higher in the ethanol seed and albedo extracts (13.05 ± 0.35 and 34.57 ± 0.09 mg gallic acid equivalent/g of extracts, respectively) compared to the hydroethanol extracts (7.88 ± 0.88 and 32.07 ± 0.67 mg gallic acid equivalent/g of extracts, respectively). The hydroethanol flavedo extract however contained significantly higher total phenolics (48.17 ± 1.17 mg gallic acid equivalent/g of extract) compared to the ethanol flavedo extract (12.50 ± 0.50 mg gallic acid equivalent/g of extract). Total flavonoid content ranged from 14.29 ± 0.38 mg quercetin equivalent/g of extract in the ethanol seed extract to 45.79 ± 1.17 mg quercetin equivalent/g of extract in the hydroethanol flavedo extract. DPPH radical scavenging activity testing revealed that the hydroethanol extracts were better inhibitors of the DPPH radical than the ethanol extracts. IC50 values ranged from 0.18 - 0.23 mg/mL for the hydroethanol extracts and from 0.26 - 0.34 mg/mL for the ethanol extracts. The hydroethanol extract of the flavedo was found to have the best ferric reducing antioxidant potential (FRAP) value (800.30 ± 1.53 μmole Fe(II)/g extract) while the seed extracts contained the lowest FRAP values (329.00 ± 1.53 and 464.30 ± 0.75 μmole Fe(II)/g extract for ethanol and hydroethanol extracts, respectively). Reducing power was observed to be higher in the hydroethanol extracts than the ethanol extracts. Inhibition of lipid peroxidation was highest in the ethanol extract of the flavedo (29.46 ± 0.08 %) and lowest in the seed extract counterpart (8.46 ± 0.15%). Our results suggest that wastes (flavedo, albedo and seeds) generated from sweet orange (Citrus sinensis) have biologically important components that may be beneficial to health.