Optimization of polyphenols extraction from grapevine canes using natural deep eutectic solvents

Canes as vineyard by-products are an underutilized resource for the recovery of polyphenols, as compounds present within these by-products still contribute to biological function that could be of interest for human health. The aim of this paper is to propose an environmentally conscious extraction method aimed towards polyphenols, providing an alternative for conventional organic solvents used. For the first time, we investigated the capacity of natural deep eutectic solvent (NaDES) to recover polyphenols from grapevine canes. Three choline chloride based NaDES systems were investigated in a first step. All were efficient to extract grapevine polyphenols and choline chloride:1,4-butanediol (BCH) provided the best results. Preliminary experiments testing solvent composition, solid to liquid ratio (SLR), temperature and time of extraction determined the experimental domain. A Box-Benhken design with water content (5-27.5-50), solid to liquid ratio (10-30-50 mg/500 mu L of BCH), temperature (20-50-80 degrees C), extraction time (5-32.5-60 min) was applied to improve both polyphenolics levels and antioxidant capacity. Multi-response optimization suggested a SLR ratio of 50 mg/500 mu L, a water content of 38.2% (w/w), a temperature of 80 degrees C and a time of extraction of 17.2 min as optimal extraction parameters. Experimental validation confirmed the predicted results obtained for the extract at optimal conditions. Phytochemical characterization showed that the optimal extract contained high proportions of stilbenes, and more particularly of trans-resveratrol and trans-epsilon-viniferin. Thus, it was shown that NaDES, as a green alternative to conventional organic solvents, are efficient to extract polyphenols from canes.