A review on source-specific chemistry, functionality, and applications of chitin and chitosan

Chitin (CT), an abundant biopolymer, next to cellulose, constitutes a vital renewable resource obtained from diverse biological sources. Chitosan (CS), its main derivative, is valued for its 'tunable' feature that facilitates numerous optimizable applications in multiple industrial sectors. The CS market is escalating exponentially, while crustaceans are majorly exploited to meet the growing demand. From the sustainability perspective, exploring alternative sources rich in CT is essential for an economical route for CS production; this can also offer a new range of functionalities and applications. This work attempts to review the properties and applications of CT and CS, based on their source (marine, terrestrial, and fungi), chemistry (structural modifications, molecular weight, and degree of deacetylation), and extraction method (chemical and biological). Critical comparisons have been made considering research reports published during the past decade. While the existing application-range for CT and CS is vast, this work concludes with future research challenges and perspectives.