Natural Deep Eutectic Solvents as a Novel Bio-Based Matrix for Ready-to-Use Natural Antioxidants-Enriched Ingredients: Extraction and Formulation Optimization

The escalating consumer demand for sustainable cosmetic ingredients poses distinct challenges, particularly concerning their stability within the final formulation. Although natural resources offer a pool of antioxidant molecules with diverse structures and polarities, achieving stabilization combined with a comprehensive antioxidant profile often proves incompatible with practical preformulation considerations. Notably, Calendula, which is rich in both polar (glycosylated flavonoids) and nonpolar (carotenoids) antioxidants, is a standout candidate. Nevertheless, the market lacks an ingredient embodying this diversity, primarily due to the limited polarity range of available usable solvents. Natural deep eutectic solvents (NaDESs) emerge as a promising solution. This study explores NaDES technology with the goal of developing a unique Calendula extract enriched in both polarities of antioxidants, a composition that is unattainable with traditional solvents. A screening of 12 NaDESs with varying polarities highlighted a NaDES based on betaine and glycerol as particularly effective, outperforming ethanol. Leveraging response surface methodology, an optimal mechanical stirring procedure for extraction was identified. The resulting extract showed a total flavonoid content of 45.42 ± 0.85 mg eq rutin/g of biomass and a total carotenoid content of 383.54 ± 4.73 µg/g biomass. It was then incorporated into a sustainable cream (1% and 10%wt) using an innovative mixing technology. The resulting creams demonstrated stability over 90 days, with no significant deviations in pH or rheological properties compared to the control, and a droplet size that was inferior to 10 µm. This study lays the foundation for pioneering natural antioxidant cocktail-loaded ingredients that are suitable for eco-friendly cosmetic formulations, substantiating the viability of integrating environmentally friendly ingredient-based solvents.