Hydrophobic eutectic solvents for extraction of natural phenolic antioxidants from winery wastewater

Global food waste is a far-reaching problem, where the recovery of high-value compounds from agri-food effluents using green solvents is an attractive valorisation strategy. Wine industry is an important business sector which generates significant volumes of wastewater, with negative economic and environmental implications. However, winery wastewater can be exploited as a rich source of phenolic antioxidants for food and fine chemical applications. For that purpose, the main goal of this work is the recovery of wine-derived phenolic compounds from liquid effluents using hydrophobic eutectic solvents (HESs). In particular, HESs composed of ammonium salts, DL-menthol and fatty acids, were prepared and evaluated for liquid-liquid extraction of phenolic compounds from synthetic winery wastewater. To achieve optimum extraction performance, the experimental conditions were optimized, including extraction time, solvent to feed volume ratio, dilution factor and type of HESs. The extraction method developed was used for the efficient extraction of natural antioxidants from wine-derived samples and gallic acid from aqueous solutions. The extracted phenolic compounds were quantified and determined by spectrophotometric methods and high-performance liquid chromatography (HPLC). The experimental results showed satisfactory recoveries of the target compounds within the range of 64.14-84.10% from winery wastewater and recoveries between 74.86 and 92.31% from gallic acid solutions. Chloride ammonium salts-based HESs, especially N8881Cl-DL-Menthol and N8881Cl-Octanoic acid, proved the highest potential for phenolic compounds recovery from winery wastewater matrices and aqueous solutions. Finally, the antioxidant capacity of the extracts was confirmed.