In-depth study on the extraction and mechanism of high-purity chitin based on NADESs method

Deep eutectic solvents (DESs) have been widely applied in biomass extraction due to their low toxicity, low cost, easy degradability, and other excellent characteristics. However, there are few reports on extraction of chitin, an important part of biomass, via DESs method, let alone the study of its related mechanism. Therefore, a novel natural deep eutectic solvents (NADESs) system consisting of lactic acid and choline chloride was proposed for the extraction of chitin. After optimizing the reaction process conditions, the obtained chitin with high purity up to 99.33% was prepared, which was comparable to the results obtained by the conventional method. And analysis results of the aforementioned products showed that the prepared chitin was acylated with a degree of 0.43. Moreover, the potential mechanism in the preparation process was explored. Free H+ in NADESs was confirmed to be the main reason for decalcification. Meanwhile, by constructing covalent bond, the hydrogen bond in NADESs was able to dissolve the protein bound to chitin, and then forming a new NADESs system, which further verified the essence of the acylation phenomenon was dehydration condensation between acid and -OH of chitin. Most importantly, the experiments as well as in-deep theoretical studies provide a directional reference that preparation of chitin from marine sources can be realized by utilizing natural resources.