(−)-Epicatechin Solubility in Aqueous Mixtures of Eutectic Solvents and Their Constituents

(−)-Epicatechin is a polyphenol present in diverse natural sources. It shows positive human health effects, which makes it interesting for the pharmaceutical and food industries. Conventional solvents used for polyphenol extraction are mostly toxic and flammable, leaving unwanted impurities in the final product. Thus, solubility of (−)-epicatechin at 101.3 kPa and 293.15, 303.15, and 313.15 K was experimentally measured in water and binary systems composed of 25 wt % of water + 1,3-propanediol (13PD), glycerol (Gly), and two deep eutectic solvents based on choline chloride as hydrogen-bond acceptor and the previous polyols as hydrogen-bond donors (DES1 and DES2). Solubility results in water were obtained using spectrophotometric and gravimetric methodologies. Overall, (−)-epicatechin solubility varies widely among the studied solvents but only slightly within the experimental temperature range. Solvents in ascending order according to (−)-epicatechin solubility are water < Gly + water < 13PD + water < DES2 + water < DES1 + water. The solubility of (−)-epicatechin is significantly enhanced by introducing choline chloride into the investigated hydrogen-bond donors (HBDs) at a molar ratio of 1:3, accompanied by 25 wt % water. Perturbed-chain statistical associating fluid theory (PC-SAFT) solubility calculations were in quantitative agreement with experimental data.