A Green and Innovative Waste Valorization Approach for Extraction of Flavonoids from Grapefruit Peels by...

Grapefruit is rich in flavanones, particularly naringin and narirutin. This study investigated the effects of temperature, time, and solid-to-liquid ratio on microwave-assisted pressurized CO₂-H₂O (MWP-CO₂-H₂O) extraction of flavonoids from grapefruit and optimized the parameters for maximum total flavonoid content (TFC) using response surface methodology. Independent variable ranges were 110-160 °C, 4.00-14.00 min, and 1:10.00-1:40.00 g/mL. Optimum conditions were 128 °C, 13.88 min, and 1:31.35 g/mL, yielding a TFC of 27.96 ± 1.29 mg naringin equivalent/g dry weight. Under these conditions, extraction yield, total phenolic content, ferric reducing ability of plasma, cupric reducing antioxidant capacity, and DPPH IC₅₀ were 55.17 ± 1.90% (dry basis), 25.42 ± 1.39 mg gallic acid equivalent/g, 39.16 ± 1.61 µmol trolox equivalent/g, 81.64 ± 0.29 µmol trolox equivalent/g, and 1.60 ± 0.01 mg/mL, respectively. Compared to conventional extraction (CE), MWP-CO₂-H₂O produced higher TFC, phenolic content, and antioxidant activity, while reducing extraction time by 13.68-fold. These results highlight grapefruit peel waste as a sustainable source of bioactive compounds and demonstrate that MWP-CO₂-H₂O is an environmentally sustainable, efficient alternative to conventional methods.