ULTRASOUND-ASSISTED EXTRACTION OF EPICATECHIN FROM LYCHEE PEEL USING A CHOLINE CHLORIDE–UREA–CITRIC ACID DEEP EUTECTIC SOLVENT

Lychee peel is an agro-industrial by-product rich in phenolic compounds and has potential as a source of value-added bioactive molecules. Among these compounds, epicatechin is particularly relevant because it is a characteristic flavan-3-ol of lychee peel and is associated with the antioxidant potential and procyanidin profile of this plant matrix, furthermore, its presence adds functional value to the extracts and reinforces the potential use of lychee peel as a source of bioactive compounds. This study aimed to evaluate the performance of a deep eutectic solvent composed of choline chloride, urea, and citric acid at a molar ratio of 1:2:0.5 for the ultrasound-assisted extraction of epicatechin from lychee peel, using water as the reference solvent. Extractions were performed at 60% amplitude for 15 min and at a solid-to-solvent ratio of 0.1 g mL^-1. The pure eutectic solvent, the eutectic lychee extract, and the aqueous lychee extract were characterized for water activity using a water activity meter, viscosity using a rotational viscometer, pH using a calibrated pH meter, and electrical conductivity using a conductivity meter. Epicatechin was quantified in the extracts by high-performance liquid chromatography. The pure eutectic solvent exhibited a water activity of 0.502 ± 0.001, viscosity of 45.10 ± 0.17 cP, pH of 1.52 ± 0.06, and electrical conductivity of 9.80 ± 0.07 µS cm^-1. After extraction, the eutectic lychee extract showed higher water activity (0.671 ± 0.001) and electrical conductivity (18.35 ± 0.02 µS cm^-1), together with a marked reduction in viscosity (13.20 ± 0.01 cP), while the pH remained practically unchanged (1.54 ± 0.01). The aqueous lychee extract presented a water activity of 0.998 ± 0.001, viscosity of 2.80 ± 0.17 cP, pH of 4.46 ± 0.05, and electrical conductivity of 1.13 ± 0.01 µS cm^-1. Epicatechin concentrations reached 4.601 mg L^-1 in the eutectic extract and 3.593 mg L^-1 in the aqueous extract, corresponding to a 28.1% higher concentration when the eutectic solvent was used. This improved recovery may be attributed to the acidic and highly interactive hydrogen-bonding environment of the eutectic system, which can enhance epicatechin solubilization despite its higher viscosity. The reduction in viscosity and the increase in conductivity after extraction suggest incorporation of water and soluble constituents from the plant matrix, increasing ionic mobility and favoring mass transfer during sonication. Overall, the choline chloride:urea acid eutectic solvent showed greater efficiency than water for targeted epicatechin recovery and represents a promising and potentially more sustainable alternative for lychee peel valorization.

The authors gratefully acknowledge CAPES; Instituto Federal do Paraná (IFPR), Fundação Araucária (Process number PRD2023361000078), and the Secretaria da Ciência, Tecnologia e Ensino Superior do Paraná (SETI) for their financial and institutional support.