How are chitosan oligomers produced?
Chitosan polymers can be partially depolymerized to yield chitosan oligomers, using either chemical methods (typically partial acid hydrolysis which however can lead to concomitant reduction of the degree of acetylation) or enzymatic treatment using chitinase or chitosanase. Depending on the conditions used, and even more so on the enzyme used, cleavage of glycosidic bonds will occur at different positions within the polymer, leading to slightly different oligomers produced. As an example, chitinases will preferentially cleave at highly acetylated regions while chitosanases will prefer higly deacetylated regions. Thus, the oligomers will differ (e.g. in their degree of acetylation), and so will potentially non-hydrolyzed remaining polymeric parts. In any case, these processes yield mixtures of chitosan oligomers, from which oligomer fractions of a specific degree of polymerization can be produced by chromatographic separation. Subsequently, these mixtures can be further separated according to their degree of acetylation, yielding mixtures of isomeric oligomers differing only in their pattern of acetylation which cannot be further separated so far. Alternatively, chitosan oligomers can be produced by partial chemical or enzymatic deacetylation of chitin oligomers, or by partial chemical or enzymatic N-acetylation of glucosamine oligomers. Also, chitosan oligomers may be produced biotechnologically in microbial cell factories, i.e. E. coli cells expressing a bacterial chitin synthase gene along with a chitin deacetylase gene leading to cytoplasmic production of defined chitosan oligomers in gram quantities. Pure paCOS are not currently available commercially.