Extraction of Chitin from Food Waste Using Recyclable Deep Eutectic Solvents

Deep eutectic solvents (DESs) are considered green due to their low cost, nontoxicity, low flammability, and biodegradability. Although the DESs-based method has been applied for chitin extraction, the efficiency of protein leaching from crustacean shells and the cyclic performance of DESs have not been thoroughly evaluated. In this study, chitin was extracted from crab shells using the DES consisting of choline chloride and lactic acid, achieving a purity of up to 95.14% by optimizing the reaction conditions and minimizing energy consumption. The kinetics of protein leaching were investigated, revealing that protein first diffused across the surface of the shells and subsequently entered the DES through pore diffusion. Mechanistic analysis showed that lactic acid effectively removed calcium carbonate from the crab shells, while protein leaching primarily relied on hydrogen bonding interactions. During the extraction process, lactic acid was consumed to remove calcium carbonate, necessitating the addition of a certain amount of lactic acid after each cycle to maintain the optimal choline chloride/lactic acid ratio. The results demonstrated that the purity and yield of chitin extracted by the DES remained relatively stable after five cycles. This cycling method of the DES supplemented with lactic acid is expected to achieve green and sustainable extraction of high-purity chitin from crab shells.