Exploring Natural Deep Eutectic Solvents (NADESs) for Extraction of Antioxidant Compounds from Aromatic Herbs used in Mediterranean Diet

Aromatic herbs are a fundamental component of the Mediterranean Diet (MD), enhancing the flavor of dishes and serving as a healthier substitute for salt. This not only enhances to the overall appeal of the diet, but also contributes to its health benefits, due to the richness of these herbs in bioactive molecules, such as phenolics, which possess antioxidant properties. The extraction of these compounds represents a crucial phase in their application in various industries. However, the use of conventional solvents poses risks to both the environment and human health. Green solvents, such as Natural Deep Eutectic Solvents (NADESs), have been identified as promising alternatives due to their non-toxic, eco-friendly, and less energy-demanding nature. The objective of this study was to assess the efficacy of two NADESs, namely glycerol--urea (Gly:U) (1:1) and choline chloride--lactic acid (CC:LA) (1:3), in comparison to the conventional solvent methanol for the extraction of phenolic compounds from six aromatic herbs which are commonly used in the MD: Mentha spicata L., Coriandrum sativum L., Rosmarinus officinalis L., Thymus vulgaris L., Ocimum basilicum L., and Origanum vulgare L. Extracts were obtained via ultrasound-assisted extraction. Phenolic and flavonoid contents were measured spectrophotometrically, and antioxidant activity was assessed via DPPH and ORAC assays. The results revealed higher phenolic concentrations in NADES extracts compared to methanol. O. vulgare extracted with Gly:U exhibited the highest phenolic content (99.45 ± 6.63 mg_GAE/g_DW), while M. spicata with Gly:U showed the highest flavonoid content (39.95 ± 0.55 mg_QE/g_DW). NADES extracts also demonstrated superior antioxidant activity in both assays. The findings suggest that extractions using NADESs are more effective than conventional solvents for extracting phenolics and promoting bioactivity. These green solvents are aligned with sustainable practices for use in various industries, thereby enhancing the valorization of Mediterranean herbs.