Simultaneous Optimization of Polyphenol Content and Antioxidant Capacity of Extracts from Habanero Pepper Leaves Obtained with Green Technologies: NADES and Ultrasound

Habanero pepper leaf, annually discarded as a by-product, is a source of phenolic compounds with functional activity. However, their recovery requires sustainable strategies that overcome the limitations of conventional organic solvents and low extraction yields. In this study, a sustainable and adjustable approach for phenolic compound recovery was developed using natural deep eutectic solvents (NADES) combined with ultrasound-assisted extraction and optimized by response surface methodology. Initially, different hydrogen bond donors (HBDs) like glycerol, glucose, and fructose (Fru), molar ratios (MR) of choline chloride (ChCl):HBD (1:1 mol/mol–1:2 mol/mol), and added water (Aw, 50–70%) were evaluated. The ChCl:Fru system (1:1 mol/mol, 70% Aw) was identified as the most efficient, showing the highest total polyphenol content (TPC) and antioxidant capacity (Ax). Simultaneous optimization yielded 147.30 ± 2.71 mg gallic acid equivalent/100 g dry leaf (DL) and 93.00 ± 0.14% Ax (predictive capacity, error < 5%). UPLC analysis identified protocatechuic acid (1285.98 ± 2.83 mg/100 g DL) and catechin (131.82 ± 0.99 mg/100 g DL) as the major compounds during the optimization process with Fru. These results position NADES as a sustainable tool for habanero pepper leaf valorization and targeted phenolic recovery, while designing greener extraction processes for agro-industrial residues.