Chitosan, an amino polysaccharide mostly derived from crustaceans, has been recently highlighted for its biological activities that depend on its molecular weight (MW), degree of deacetylation (DD), and acetylation pattern (AP). More importantly, for some advanced biomaterials, the homogeneity of the chitosan structure is an important factor in determining its biological activity. Here we review emerging enzymes and cell factories, respectively, for in vitro and in vivo preparation of chitosan oligosaccharides (COSs), focusing on advances in the analysis of the AP and structural modification of chitosan to tune its functions. By 'mapping' current knowledge on chitosan's in vitro and in vivo activity with its MW and AP, this work could pave the way for future studies in the field.
Crustacean waste, consisting of shells and other inedible fractions, represents an underutilized source of chitin. Here, we explore developments in the field of crustacean-waste-derived chitin and chitosan extraction and utilization, evaluating emerging food systems and biotechnological applications associated with this globally abundant waste stream. We consider how improving the efficiency and selectivity of chitin separation from wastes, redesigning its chemical structure to improve biotechnology-derived chitosan, converting it into value-added chemicals, and developing new applications for chitin (such as the fabrication of advanced nanomaterials used in fully biobased electric devices) can contribute towards the United Nations Sustainable Development Goals. Finally, we consider how gaps in the research could be filled and future opportunities could be developed to make optimal use of this important waste stream for food systems and beyond.