Chitosan is produced by the alkaline N-deacetylation of chitin, the second most abundant natural polymer after cellulose. Commercial chitosan is sourced from shrimp and crab shell waste, though fungal sources (Aspergillus niger) are available for allergen-free applications.
The degree of deacetylation (typically 75–95%) and molecular weight (low, medium, or high) determine its functional properties: solubility in dilute acid, viscosity, film-forming ability, and antimicrobial activity. Chitosan is approved for food contact use in Japan, Korea, and several other countries; it holds GRAS status in the US for specific applications. It is a permitted dietary supplement ingredient and is increasingly used as a natural food preservative due to its antimicrobial and antioxidant properties.