Natural Deep Eutectic Solvents as Sustainable Extractants of Phenolic and Antioxidant Compounds from Raw and Roasted Arabica Coffee Beans

Natural deep eutectic solvents (NADES) have emerged as sustainable alternatives to conventional organic solvents for recovering bioactive compounds from plant matrices. In coffee, however, information regarding their performance in raw and roasted beans remains limited. Therefore, this study evaluated the chemical composition of raw and roasted Arabica coffee beans (RaACB and RoACB) of the Yellow Bourbon variety and investigated the efficiency of four NADES formulations for extracting phenolic compounds. Four NADES systems were prepared by combining citric acid with glucose (2:1 M, N1) or glycerol (1:1 M, N2), and glucose with glycerol at ratios of 1:1 M (N3) and 1:2 M (N4). Solvents were obtained under stirring at 50 °C with the addition of 30% distilled water. Ground coffee samples (0.2 g) were extracted with 20 mL of solvent using ultrasound-assisted extraction for 75 min, followed by vacuum filtration. Extracts obtained with previously optimized 70% ethanol were used as controls, and a coffee beverage was prepared for comparison with roasted coffee extracts. Total polyphenol content (TPC) was determined by the Folin–Ciocalteu assay, while antioxidant activity (AA) was evaluated by the FRAP method. Because some NADES components exhibited intrinsic antioxidant activity, blank values were subtracted from extract results. Roasting significantly affected coffee composition. Raw beans showed higher soluble solids (29.11 ± 0.51%) and free amino acid contents (823.27 ± 14.15 mg AGE/100 g) than roasted beans (22.41 ± 0.32% and 205.68 ± 6.76 mg AGE/100 g, respectively), whereas titratable acidity increased after roasting (215.63 ± 16.97 versus 124.14 ± 5.66 mL NaOH 0.1 N/100 g), reflecting chemical transformations associated with thermal processing. The highest TPC values for both coffee samples were obtained with 70% ethanol, reaching 10864.47 ± 354.49 mg CAE/100 g in RaACB and 11084.85 ± 258.89 mg CAE/100 g in RoACB, without statistical differences between them. Among the NADES formulations, N1 showed lower extraction efficiency for RaACB (5065.03 ± 190.60 mg CAE/100 g), but was the most effective for RoACB (6932.24 ± 128.72 mg CAE/100 g), producing values statistically similar to the beverage (6599.37 ± 154.03 mg CAE/100 g). Antioxidant activity presented a different profile from TPC. The greatest FRAP values were observed for N2, with 273272.33 ± 8873.52 and 309512.03 ± 17708.17 µmol TE/100 g for RaACB and RoACB, respectively, followed by N1. Ethanol extracts exhibited considerably lower antioxidant activity, while N3 and N4 showed the least efficient performance. The beverage displayed antioxidant values comparable to ethanol, N3, and N4 extracts. Overall, NADES containing citric acid, particularly the citric acid–glycerol system, demonstrated superior antioxidant extraction capacity and represent a promising green alternative for recovering bioactive compounds from both raw and roasted Arabica coffee beans.

Acknowledgments: IAC; EMBRAPA – CONCAFÉ. Project: 2018.20016.00.04. Scholarships: 2978, 2250, and 2358.