PHENOLIC CONTENT, ANTIOXIDANT PROPERTIES AND HPLC PROFILES OF GRAPE SEED EXTRACTS OBTAINED WITH NATURAL DEEP EUTECTIC SOLVENTS

Brazil is the third-largest wine producer in Latin America, with an estimated production volume of 2.7 million hectoliters in 2024. However, wineries generate large volumes of waste (nearly 5 tons of solid waste/ha) and other by-products; these include grape stalks and pomace/seeds. This waste requires appropriate valorization and management to minimize environmental damage. Grape seeds are rich in phenolics, and antioxidants having numerous health benefits and can be used as food additives and effective functional raw materials for anti-aging cosmetics. Natural deep eutectic solvents (NADES) possess desirable properties as solvents, including low toxicity, biodegradability, and high solubility for a wide range of compounds and are promising green solvents for the extraction of bioactive compounds from natural sources. Therefore, the goal of this work was to evaluate NADES as alternative to conventional solvents for recovering phenolics from grape seeds (Vitis labrusca). Four choline-based deep eutectic solvents (ChCl:citric acid (1:1), ChCl;oxalic acid (2:1), ChCl:glucose (2:1), and ChCl:urea (1:1)), and sodium acetate:urea (1:3) were prepared and previously characterized. The optimal extraction conditions were determined as 30 min in an ultrasound bath at 40 °C, with a solvent-to-grape seed ratio of 20:1. The aqueous ethanol (70% v/v) was used as reference solvent and extracts were evaluated for total phenolic content (TPC) using the Folin-Ciocalteu method, antioxidant activity through DPPH and ABTS free radical scavenging assays, and their phenolic profiles were characterized via HPLC-DAD. The ChCl:urea showed the highest TPC value (0.40 ± 0.01 GAE/mL) and the maximum total antioxidant capacity, showing free radical scavenging potentials of 84 ± 1.0% and 52 ± 0.8% for DPPH and ABTS assays, respectively. The chromatographic profile of the ChCl:urea extract was very similar to that of the reference extract, concerning the major compounds with typical UV spectra of phenolic acids (e.g., gallic acid) and flavanols (e.g., catechin). This study demonstrated that NADES could be an alternative for the extraction and quantitative assessment of active bioactive compounds from grape seeds and contribute to the valorization of winery waste.