Developing a recovery process for bioactives from discarded by-products of winemaking industry based on multivariate optimization method: Deep eutectic solvents as eco-friendly extraction media.

Introduction: The recovery process for bioactives from discarded by-products of the winemaking industry is of great value considering both environmental and economic aspects.

Objective: The goal of this study is to investigate the extraction of phenolic antioxidants from grape (Vitis vinifera) seeds by means of carboxylic acid-based deep eutectic solvents (DESs) in order to propose an environmentally friendly method based on a multivariate optimization approach.

Material and methods: Carboxylic acid-based DESs were designed with several molar ratios (1/1, 1/2, and 2/1). Two polyols (glycerol and ethylene glycol) were used as hydrogen bond donors, while formic acid, acetic acid, and propionic acid were selected as hydrogen bond acceptors. The process parameters (water content, extraction time, and solid mass) were analyzed to optimize the process through Box-Behnken design with response surface method, after determination of the best combination for the highest total phenolic content (TPC) and the antioxidant activity yields.

Results: The maximum TPC yield (153.17 ± 0.003 mg-GAE/g-GS) and antioxidant activity yield (82.26 ± 0.004 mg-GAE/g-GS) were achieved by 50% water addition into the DES (ethylene glycol/acetic acid, 1/1), 85 sec extraction time, and 0.1 g grape seed.