This review provides an overview of recent developments in Citrus aurantium L. (sour or bitter orange), focusing on its bioactive compounds, innovative extraction techniques, and technological applications. C. aurantium is rich in bioactive compounds such as flavonoids (naringin, hesperidin, kaempferol, quercetin), essential oils (β-pinene, limonene), and vitamin C, which represents significant biological activities including antioxidant, antimicrobial, anti-inflammatory, and anticancer effects. The review discusses traditional extraction methods, such as solvent extraction and hydrodistillation, alongside newer, eco-friendly approaches like ultrasound-assisted extraction, microwave-assisted extraction, supercritical fluid extraction, and natural deep eutectic solvents. It also highlights cutting-edge techniques, including molecular imprinting polymer-based extraction, which enable the more efficient enrichment and purification of specific compounds like synephrine. Finally, the review examines the diverse industrial applications of these bioactive compounds in sectors such as foods, pharmaceuticals, and cosmetics, while emphasizing the growing need for sustainable and efficient extraction technologies.

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 (NADESs) 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, obtained after 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% AW exhibited the highest quercetin + luteolin extraction (721.32 mg/100 g dry mass), both at the same MR (1:1 mol/mol). Glycerol also achieved the highest recovery of total flavonoids (1829.7 ± 17.85 mg quercetin equivalent/100 g dry mass) with an MR of 1:2 mol/mol and 70% AW. Finally, all other maximum values were obtained with fructose-based NADESs: the highest total phenolic content (3603. 7 ± 52.9 mg gallic acid equivalent/100 g dry mass) was achieved at an MR of 1:1 mol/mol and 50% AW, while for both vitamin C (1964.8 ± 33.7 mg ascorbic acid equivalent/100 g dry mass) and antioxidant capacity (84.31% inhibition), the maximum was reached at an MR of 1:2 mol/mol and 50% AW.

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.

Citrus aurantium L. by-products are a valuable source of bioactive compounds with potential industrial applications. This study evaluated the use of natural deep eutectic solvents (NADESs), formulated with choline chloride as the hydrogen bond acceptor (HBA) and fructose as the hydrogen bond donor (HBD), combined with ultrasound-assisted extraction to optimize the recovery of flavonoids from Citrus aurantium L. industrial by-products. A central composite design (CCD) was employed to optimize total flavonoid content (TFC). The molar ratio (MR; 1 and 2 mol of HBD per mol of HBA) and the percentage of added water (AW; 40 and 60%) were optimized. In addition to TFC, total phenolic content (TPC), total ascorbic acid (TAA), antioxidant capacity (Ax) and phenolic profiles were also evaluated. The optimal extraction conditions, as obtained by Response Surface Methodology (RSM) for TFC, corresponded to an HBD molar ratio of 1.33 per 1 mol of HBA and 47.48% added water, resulting in an optimal value of 1576.63 ± 4.9 mg quercetin equivalents (QE)/100 g dry mass (DM). Maximum values of 4276.94 ± 25.4 mg gallic acid equivalents (GAE)/100 g DM for TPC, 2077.66 ± 21.3 mg/100 g DM for TAA and 88.09 ± 0.1% inhibition for Ax were also obtained. The optimal NADES was characterized by density, viscosity, pH, Fourier-transform infrared (FTIR) and Raman spectroscopy. Additionally, phenolic profiling revealed high concentrations of hesperidin (2747.1 mg/100 g DM), naringenin (1251.93 mg/100 g DM), and quercetin + luteolin (660.65 mg/100 g DM).