What are chitin oligomers?
Chitin polymers can be partially depolymerized to yield chitin oligomers, using either chemical methods (typically partial acid hydrolysis which however can lead to concomitant partial de-N-acetylation, yielding chitosan oligomers) or enzymatic treatment using chitinase. There is no clear distinction between chitin oligomers and chitin polymers. Typically, chitin oligomers are defined as short chains of up to ten monomeric units of N-acetylglucosamine. Their names reflect their degrees of polymerization (DP): DP 2 = dimer, DP 3 = trimer, DP 4 = tetramer, DP 5 = pentamer, DP 6 = hexamer, DP 7 = heptamer, DP 8 = octamer, DP 9 = nonamer, DP 10 = decamer. Chitin oligomers up to the size of hexamer are soluble, hepta- and octamer are poorly soluble, and larger oligomers are essentially insoluble in water. Chitin oligomers are known to be recognized by and stimulate the immune system of humans and higher animals, and they can also trigger disease resistance reactions in plants. Chitin oligomers are sometimes also called chito-oligosaccharides and abbreviated as COS, but the term is ambiguous and not clearly defined.