Abstract
In this examination, two glycerol-based deep eutectic solvents (DESs) were tested for their efficiency in the recovery of antioxidant polyphenols and anthocyanin pigments from red grape pomace (RGP). The two DESs synthesized had sodium acetate and sodium benzoate as hydrogen bond acceptors, to test the role of the hydrogen bond acceptor polarity on the extraction performance. Furthermore, the process was enhanced by an ultrasonication pretreatment stage. After initial testing with respect to water content, ultrasonication power and liquid-to-solid ratio, the DES composed of glycerol and sodium benzoate (GL-SBz) was shown to be significantly more efficient than the one made of glycerol and sodium acetate (GL-SAc). Further optimization of the extraction with regard to time and temperature demonstrated GL-SBz to be a highly effective solvent for the production of RGP extracts rich in polyphenols including gallic acid, catechin and quercetin, and pigments including malvidin 3-O-glucoside p-coumarate and malvidin 3-O-glucoside. The extracts produced also had significantly higher antiradical activity and reducing power compared to those generated with aqueous ethanol or water. From this study, evidence emerged regarding the role of the hydrogen bond acceptor nature in the extraction efficiency of polyphenols. The process developed is proposed as a green, high-performing methodology for the production of RGP extracts with enhanced polyphenolic content and antioxidant activity.
Highlights
The agri-food sector embraces industrial activities that largely pertain to the processing of plant-based materials, accompanied by ever-increasing amounts of associated wastes.The residual biomass which is regularly rejected as a result of plant tissue processing encompasses materials rich in organic substances, such as small branches, leaves, peels, seeds and roots
The testing of a deep eutectic solvents (DESs) composed of glycerol (HBD), and sodium acetate, sodium propionate and sodium butyrate (HBAs) showed that the organic anion chain length might affect DES polarity to a significant extent, affecting polyphenol extractability [13]
Two glycerol-based DESs having hydrogen bond acceptors with different polarities were tested for their efficiency in recovering red grape pomace (RGP) polyphenols
Summary
The agri-food sector embraces industrial activities that largely pertain to the processing of plant-based materials, accompanied by ever-increasing amounts of associated wastes.The residual biomass which is regularly rejected as a result of plant tissue processing encompasses materials rich in organic substances, such as small branches, leaves, peels, seeds and roots. The agri-food sector embraces industrial activities that largely pertain to the processing of plant-based materials, accompanied by ever-increasing amounts of associated wastes. Vinification activities are crucial for the economies of several countries and, as estimated by the OIV, wine production in 2020 reached almost 258 million hectoliters [2]. The winemaking process inevitably generates a large volume of wastes, which represent about 13 to 20% of the initial grape mass. These residues are composed mainly of pomace (seeds and skins), stems, and wine lees, and they bear a high content of polyphenolic substances. By virtue of the multitude of biological properties [3], several classes of this family of secondary metabolites have been extensively studied and numerous methodologies have been applied for the efficient recovery of polyphenols from vinification wastes [4]
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