Temperature-responsive deep eutectic solvents as green and recyclable media for the efficient extraction of polysaccharides from Ganoderma lucidum

Recently, more and more attention has been paid to the green and recyclable deep eutectic solvents (DESs) in the extraction and separation field. In this study, nine temperature-responsive deep eutectic solvents (TRDESs) were prepared and developed to extract polysaccharides from Ganoderma lucidum (G. lucidum). The polysaccharides were extracted into a homogeneous solution above the upper critical solution temperature (UCST) of TRDESs. The factors influencing the solid-liquid extraction were investigated, including type and concentration of TRDESs, liquid-solid ratio, extraction temperature, extraction time, and pH. Then, two phases formed below the UCST of TRDESs with the polysaccharides being recovered in the aqueous phase and TRDESs being recycled and reused. The cyclic stability of TRDESs was evaluated by studying the extraction ability of extractant, structure and activity of polysaccharides after several recycles of TRDESs. Finally, the hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) of TRDESs can be recovered by using carbon dioxide and nitrogen after the cyclic tests. Further studies of density functional theory (DFT) calculations proved that the hydrogen bond interaction was the main factor affecting this extraction, and meanwhile the HBAs played the dominant role in this process. This study gives some guidance for the exploration and application of recyclable DESs for the green and sustainable extraction of various bioactive compounds from plant resources.