Natural Deep Eutectic Solvent for Extracting Antioxidants From Spent Coffee Grounds and Improving Stability of Chlorogenic Acid Against Heat and Light Stress

Spent coffee grounds (SCG), by-products of the coffee brewing process, are rich sources of bioactive compounds having antioxidant properties. This study evaluated the potential of natural deep eutectic solvent (NaDES) as an eco-friendly solvent to extract antioxidants from SCG and improve their stability. Twenty-nine types of NaDES were prepared to evaluate extraction capability, while the storage stability of chlorogenic acid in selected NaDES was monitored under 60°C thermal and light conditions. Proline-based NaDES systems with lactic or citric acid showed the highest extraction efficiency, significantly enhancing antioxidant activity, total phenolic content, and chlorogenic acid content compared to deionized water (DW). Under thermal stress and riboflavin photosensitization, chlorogenic acid in NaDES extracts decomposed by only 3.9%-11.4% and 7.3%-11.3%, whereas the DW extract exhibited 36.3% and 74.5% degradation, respectively. Therefore, NaDES is a promising alternative to conventional solvents for phenolic recovery from SCG, utilizing robust hydrogen-bond networks to substantially increase compound stability. PRACTICAL APPLICATIONS: This study evaluates the potential of extracting antioxidants and eco-friendly upcycling by using natural deep eutectic solvent from discarded spent coffee grounds. This solvent not only increases extraction efficiency but also effectively prevents major antioxidants from being destroyed by heat and light. This natural extract has potential for future applications as an additive in functional foods, beverages, and cosmetics and can help maintain quality by preventing the loss of active ingredients during processing and distribution of products.