Influence of Natural Deep Eutectic Solvent Compositions on the Polyphenol Profile of <em>Citrus aurantium</em> By-Products from Yucatán, México

In the Yucatán Peninsula, Citrus aurantium L. has a strong cultural and culinary relevance where local industries already process its juice and essential oils, producing large amounts of by-products. In this context, green chemistry strategies have accelerated the valorization of agro-industrial residues, where natural deep eutectic solvents (NADES) stand out due to their low cost, ease of preparation, and high extraction efficiency. This study focuses on evaluating different NADES combinations for the extraction of bioactive compounds from C. aurantium by-products, followed by essential oil (cold pressing) and juice (mechanical pressing) extraction. A 3×2×2 factorial design was implemented to evaluate the effect of hydrogen bond donor (HBD: fructose, glucose and glycerol), molar ratio (MR: 1:1 and 1:2 mol/mol choline chloride (ChCl) :HBD and added water (AW: 50 and 70%) on the polyphenolic profile, total phenolic content, total flavonoid content, ascorbic acid content and antioxidant capacity. HBD was the most critical factor in the extraction of bioactive compounds, the extract obtained with glycerol and 70% AW exhibited the highest hesperidin content (2186.08 mg/100 g dry mass), while the same HBD with 50% added water exhibited the highest quercetin + luteolin extraction (721.32 mg/100 g dry mass), both at same MR (1:1 mol/mol). Glycerol also achieved the highest recovery of total flavonoids (1829.7 ± 17.85 mg quercetin equivalent/100g dry mass) with a MR of 1:2 mol/mol and 70% AW. Finally, all other maximum values were obtained with fructose-based NADES: the highest total phenolic content (3603. 7 ± 52.9 mg gallic acid equivalent/100 g dry mass) was achieved at MR of 1:1 mol/mol and 50% AW, while for both, vitamin C (1964.8 ± 33.7 mg ascorbic acid equivalent/100g dry mass) and antioxidant capacity (84.31% inhibition) the maximum was reached at MR of 1:2 mol/mol and 50% AW.