Unraveling the utilization feasibility of citrus peel solid distillation waste as potential source for antioxidant as well as bioethanol

Waste materials in large amount are being generated as distillation waste while essential oil from citrus peels is extracted. These peels are rich in phenolic compounds as well as dietary fibers, a prominent source for nutraceuticals together with bioethanol. In this present study, distillation wastes of three different citrus peels (kinnow, mosambi, and orange) were explored for extraction of phenolic compounds followed by bioethanol production. Ultrasonication-mediated methanolic extract produced the highest yield (19.8–23.1%) of phenolics. Total phenol and flavonoid content in the extract was more in kinnow peels than in mosambi and orange. Antioxidant potency composite (APC) index indicated higher activity for kinnow peels (5.98, 7.67) compared to orange (6.24, 7.69) and mosambi (6.36, 7.88) peels for respective fresh and distilled materials. Residual biomass after saccharification followed by fermentation showed approximately 1.91–2.96 times higher bioethanol production potential in distilled materials compared to non-distilled ones across different peels used. Removal of d-limonene (potential inhibitor of yeast) during hydrodistillation attributed to higher bioethanol production in the distilled materials. The highest ethanol concentration was observed in orange peel (7.89 g/L followed by mosambi (7.16 g/L and kinnow (5.08 g/L). This work primarily focuses on investigating the possibilities for utilization of these wastes into valuable nutraceuticals as well as potential feedstock for bioethanol formation that can be manifested as an important source for value addition and biorefinery.