Yasmin Caroline Nóvoa Sakurai

Natural deep eutectic solvents (NADESs) of choline chloride (ChCl) and fructose, glucose, citric and malic acid with different water concentration were prepared and characterized. The pH ranged from 2.34 to 7.38. An increase in the intensity at 3300 cm⁻¹ (FT-IR), by the interaction between the receptor and the hydrogen donor, occurred. The water content increased the intensity in the OH region without changing the vibrational mode. The same behavior occurred in Raman spectra. NADES without water showed a high density (1.234 to 1.375 g/mL) and viscosity (0.09991 to 0.46921 Pa·s). NADESs with 20% and 40% water were selected for extracting phenolic compounds from araza (Eugenia stipitata), using an ultrasonic system of bath, tip, and ethanol. Araza ethanol extract had a TPC (total phenolic compounds) of 325.19 mg GAE/g, and DPPH and ABTS of 12.00 and 291.31 µmolL⁻¹ Trolox g⁻¹. ChCl:citric acid (1:1) containing 40% water was the most efficient NADES in the tip ultrasound extraction: a TPC of 273.40 mg GAE/g; DPPH and ABTS of 31.55 and 204.9 µmolL⁻¹ Trolox g⁻¹; and an extraction yield of 84% related to ethanol. NADESs as solvents can be used directly by the food industry as a final product or ingredient, without purification, and proved to be versatile, with different properties.

In this paper, natural deep eutectic solvents (NADESs) with lactic acid, glycine, ammonium acetate, sodium acetate, and choline chloride were prepared with and without the addition of water. NADES formation was evaluated using FTIR and Raman, where hydrogen bonds were identified between the hydroxyl group of lactic acid and the amino and carboxyl groups of glycine. Acetate and ammonium ions were also identified as forming bonds with lactic acid. The addition of water did not cause changes in the vibrational modes of the FTIR and Raman spectra but contributed to a reduction in NADES viscosity and density. Viscosity ranged from 0.335 to 0.017 Pa s⁻¹, and density ranged from 1.159 to 0.785 g mL⁻¹. The best results for the extraction of phenolic compounds from pitaya (dragon fruit) were achieved with an organic solvent (450. 41 mg 100 g⁻¹ dry bases-db) in comparison to NADESs lactic acid:glycine (193.18 mg 100 g⁻¹ db) and lactic acid:ammonium acetate (186.08 mg 100 g⁻¹ db). The antioxidant activity of the extracts obtained with the NADESs was not statistically different from that of the extract obtained with organic solvents.