Chemical and Biological Characterisation of Orange (Citrus sinensis) Peel Extracts Obtained by Subcritical Water

Orange peels, generally considered as waste, were treated with subcritical water (SWE)—a green technology and environmentally friendly extraction process—at different temperatures (120–200 °C) and extraction times (5–60 min). The extracts which were obtained were chemically and biologically characterised to evaluate this potential source of bioactive compounds. The extracts total phenolics content (TPC) and total flavonoids contents (TFC), as well as total antioxidant capacity (TAC), DPPH radical scavenging activity, and total carbohydrate content, were determined by UV spectrophotometry. The pectin content was quantified by a gravimetric method. The dietary fibre content was investigated, and a phytochemical screening assay was performed. The extract obtained at 120 °C for 5 min displayed the highest TPC (45.45 mg GAE/g DW), TFC (9.29 mg RE/g DW), and TAC (130.47 mg AAE/g DW), indicating that relatively low temperatures and extremely short extraction times can be used in SWE to obtain orange peel extracts that are rich in bioactive compounds. The results of this study demonstrate the exceptional potential of orange peel extracts obtained with SWE. As shown, this biowaste represents a promising source of health-promoting compounds that could be used in pharmaceutical and dietary products.