How is chitin produced commercially?
Most of the chitin available commercially is isolated from shrimp or crab shell wastes, while only a very small portion is gained from squid pens or fungal cell walls. Lately, insect chitin is also becoming available on a small scale. Thus, almost all chitin available on the market is α-chitin, only very limited amounts of β-chitin from squid are marketed. The chitin in shrimp or crab exoskeletons is embedded in a matrix of proteins and mineralized with calcium carbonate so that its extraction requires a number of consecutive steps, involving decalcification with (hydrochloric) acid followed by deproteination with caustic soda; some producers add a treatment for decolorization. In insects, the chitin is believed to be covalently linked to proteins and often embedded in catechols, requiring additional treatments. The acid and alkaline treatments typically somewhat decrease the degree of polymerization of the isolated chitin. The chitin in fungal cell walls is not calcified but it is believed to be covalently linked to glucans requiring an even more drastic acid treatment yielding rather low molecular weight chitins only. Extraction of squid pen chitin does not require an acid treatment, thus yielding very high molecular weight polymers. Enzymatic extraction procedures have been developed to replace the chemical procedures but they are not yet efficient enough for large scale commercial use.