Sustainable conversion of cottonseed hulls to valuable proanthocyanidins through ultrasound-assisted deep eutectic solvent extraction

This study presents a novel approach for converting cottonseed hulls (CSHs) into valuable proanthocyanidins (PAs) through deep eutectic solvent (DES)-based ultrasound-assisted extraction (UAE-DES). Response surface methodology (RSM) was applied to optimize and model this process, resulting in maximum yields of 78.58 mg/g. The ideal PA extraction conditions were determined to be a liquid-to-material ratio of 36.25 mL/g, a water content of 33.21%, and an extraction period of 7.4 min. Molecular dynamic simulations (MDS) were performed to study the interactions between the solvent and target chemicals. Increased van der Waals forces and stronger interactions between DES and the target chemical catechin (CA) compared to those observed with methanol or water were observed. Furthermore, the optimized extract exhibited a higher PA content than can be obtained with conventional extraction methods and demonstrated antioxidant activity in vitro. The cottonseed hulls residues (CSRs) remaining after the extraction process can be used to produce activated carbon (AC(CSR)), which has some capacity to adsorb methylene blue (MB) contaminants. This study offers a reference for the fruitful transformation of waste biomass into high-value products.