Impact of varied drying methods on the phytochemical compounds, and antioxidant, antidiabetic and anti-tyrosinase activities of Citrus aurantium

This study investigated the effects of four drying methods (freeze-drying (FD), vacuum-drying (VD), hot air-drying (HD), and sun-drying (SD)) on the phytochemical profile and bioactivities of different parts (leaves, pulps, peels, seeds) of Citrus aurantium . Quantitative analysis revealed that FD significantly ( P < 0.05) enhanced the retention of total phenolics (e.g., 25.30 ± 0.65 mg GAE/g), flavanols (0.85 ± 0.02 mg CE/g), flavonols (23.91 ± 0.78 mg RE/g) and condensed tannins (3.39 ± 0.04 mg CE/g) in leaves, concurrently yielding the strongest antioxidant (DPPH IC₅₀: 3.26 ± 0.16 mg/mL; ABTS IC₅₀: 0.81 ± 0.01 mg/mL) activity. Conversely, thermal drying methods (VD, HD) and SD were more suitable for pulps, peels, and seeds. For instance, peels and seeds treated with thermal drying methods exhibited higher anti-α-glucosidase activity significantly ( P < 0.05) than FD. UPLC-QTOF-MS/MS identified 14 phenolic and alkaloid compounds, with correlation analyses confirming that phenolic compounds were the primary contributors to the observed bioactivities. This study provides a quantitative basis for selecting optimal drying methods to maximize the bioactivity and utilization of different C. aurantium parts for functional food and pharmaceutical applications • Freeze-drying was suitable for bioactive constituent and bioactivities of leaves. • Hot drying was more appropriate for pulps, peels and seed. • Sun-drying was appropriate to release of anti-α-glucosidase constituents. • A total of 14 compounds were characterized by UPLC-QTOF-MS.