If you search the word “chitosan” on the internet, you will be fed up with the sheer number of search results. Let me select a few that drew my attention to talk with you today.
I don’t mean to obstruct someone's business, but one search result showed “squid chitosan.” Chitosan is made from chitin, which is made mostly from crab shells. To be precise, crab shell-derived chitin is called α-chitin (α-type chitin), while squid cartilage-derived chitin is called β-chitin (β-type chitin). To be more specific, α-chitin and β-chitin have identical types and number of elements composing a molecule, but differ in steric structure. In chemical terms, they are known as isomers.
So far, so good, but, this is where it gets tricky. It is wrong to think as α-chitin derived chitosan is crab chitosan, and β-chitin derived chitosan is squid chitosan. This seems right, but in fact, whether it be made from α-chitin or β-chitin, all chitosan have the same structure formula. Therefore, there is not such a thing as α-chitosan or β-chitosan.
Although there are two types of chitin, chitosan has one single structure.