Phytochemical and antioxidant profile of citrus peel extracts in relation to different extraction parameters

The citrus processing industry generates around 50% fruit waste, encompassing peels, pulp, seeds, and other residues. Citrus peel, among these by-products, contains significant amounts of bioactive compounds, representing a sustainable and renewable source of phenolics. In this context, the present study was conducted to probe phytochemical profile and antioxidant potency of orange peel extracts. Moreover, the quantification of hesperidin and nobiletin was carried out using HPLC. The extracts were obtained using water and 50% aqueous-methanol and aqueous-ethanol, separately alongside varying time intervals, i.e. 30, 45 and 60 min. The obtained extracts were then investigated for their phytochemical and antioxidant profile. Afterwards, three best treatments, one from each extracts (aqueous-ethanol, methanol, and water), were chosen based on their phytochemical profiling. The phytochemical analyses and in vitro antioxidant assays showed the highest total phenolics (2010 mg GAE/100 g), flavonoids (90 mg/100 g), and flavonols (2.2 mg/100 g) in methanolic extracts obtained at 60 min. Likewise, the highest DPPH (60.55%), antioxidant activity (51.7 %), FRAP (13.6 mg TE/g), and ABTS (7.4 mu mol TE/g) were also attributed to methanolic extract of orange peel obtained at 60 min except for antioxidant activity which was obtained at 30 min. Likewise, HPLC analysis depicted maximum content of hesperidin and nobiletin (133.70 and 8.50 mg/g) in methanol extract as compared to ethanol (98.80 and 5.50 mg/g) and water (61.90 and 1.25 mg/g), correspondingly. It was concluded that aqueous-methanol could be used as solvent of choice for isolation of orange peel flavonoids with extraction duration of 60 min. Flavonoid and antioxidant levels in orange peel extracts are significantly influenced by extraction time and solvent type.