Ultrasound-assisted NaDES extraction of phenolics from Butea monosperma flowers: Optimization and cosmetic applications

In alignment with green chemistry principles, this study presents an eco-friendly method for extracting bioactive compounds from Butea monosperma flowers using natural deep eutectic solvents (NaDES). Lactic acid (LA) was combined with various hydrogen bond acceptors, sodium acetate (SA), glucose (Glu), and fructose (Fru) to prepare NaDES. Ultrasound-assisted extraction (UAE) was employed as a green and efficient extraction technique. Extraction efficiency was optimized based on total phenolic content (TPC) and antioxidant activity, evaluated using both DPPH and ABTS assays. Optimal conditions were achieved using LA:SA (3:1, 20 % water) for 45 min (LS-1) and LA:Glu (9:1, 40 % water) (LG-1) for 60 min, yielding high TPC values (1069.49 ± 12.39 and 1064.93 ± 15.33 mg GAE/L) with strong DPPH scavenging activity (0.089 ± 0.005 and 0.055 ± 0.005 %v/v). ABTS assay further confirmed such antioxidant activity of these extracts. The crude extracts were characterized using UV and NMR spectroscopy. Two major flavonoids, isobutrin (1) and butrin (2), were successfully isolated and structurally confirmed using UV, IR, and NMR techniques. Their antioxidant activities were also confirmed by the DPPH and ABTS assays. Finally, the most potent extract, prepared using LS-1, was successfully incorporated into a water-based cosmetic formulation, demonstrating its potential for sustainable cosmetic applications.