What are the quality criteria for chitin?

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Pure chitin is an odorless white powder. High quality commercial chitin typically has ash contents below 1% and contains less than 40 ppm heavy metals. Its protein content should be below 2%. For most applications, the degree of polymerization and the degree of acetylation of chitin should be as high as possible, but both parameters are difficult to determine as chitin is crystalline and not easily soluble. Also, as the extraction procedures tend to decrease both parameters, their exact values for native chitin polymers in situ (i.e. in their natural environment, before extraction) are not known. Chitin polymers are estimated to be built of around 3,000-5,000 fully acetylated monomeric N-acetylglucosamine units and to be fully acetylated (i.e. the degree of polymerization is around 3,000-5,000, or the molecular weight is around 600 kD to 1 MDa; and the degree of acetylation is 100%). These values are estimates for crustacean chitins, less information is available for chitin from other sources, such as fungi or insects.