Synthesis and Application of Natural Deep Eutectic Solvents (NADESs) for Upcycling Horticulture Residues

Upcycling horticulture residues offers a sustainable solution to reduce environmental impact, maximize resource utilization, mitigate climate change, and contribute to the circular economy. We synthesized and characterized 14 natural deep eutectic solvents (NADESs) and applied them to upcycle horticulture residues, offering an innovative valorization approach. Using an initial many-factors-at-a-time (MFAT) screening followed by a rotatable central composite response surface methodology (RCCRSM) for optimization, quadratic models fitted the response data for all the synthesized NADESs given: TPC (R2 = 0.984, p < 0.0001), TFC (R2 = 0.9999, p < 0.0001), AA-CUPRAC (R2 = 0.918, p < 0.0001), FRAP (R2 = 1.000, p < 0001), and DPPH (R2 = 0.9992, p < 0.0001). An ultrasound temperature of 45 °C, extraction time of 5 min, solvent volume of 25 mL, and solvent concentration of 90% (v/v) were considered the optimal conditions for achieving maximum desirability (0.9936) for TPC yield. For TFC and CUPRAC, the optimal conditions were 30 °C, 5 min, 25 mL, and 90% (v/v), with maximum desirability values of 0.9003 and 1.00, respectively. The maximum desirability for FRAP (0.9605) was achieved under conditions of 45 °C, 25 min, 25 mL, and 50%, while DPPH had a maximum desirability of 0.9313, with 50 °C, 15 min, 15 mL, and 70% (v/v) as the optimized conditions.