Pretreatment in Hot Glycerol for Facile and Green Separation of Chitin from Prawn Shell Waste

A rapid and efficient process for the separation of chitin from waste prawn shells using hot glycerol pretreatment is reported. The pretreatment of waste prawn shell in hot glycerol enables the removal of protein possibly through dehydration and temperature induced fragmentation into low molecular weight water-soluble fragments, which are subsequently removed from the shell matrix by dissolution in water. In contrast, in the industrial process of preparing chitin from crustacean shells, the deproteinization is carried out with hot aqueous sodium hydroxide. The novel pretreatment present here should be applicable to all crustacean shell waste, in principle. Chitin was isolated by two different methods after the pretreatment in glycerol. In one of the methods, the pretreated shells were treated directly with citric acid to remove protein and minerals (mostly as calcium citrate). In the second method, the pretreated shells were ground and rinsed with water to remove protein fragments and part of the minerals (mostly as calcium carbonate). In the subsequent step, the residual minerals were demineralized with citric acid. The later method offers the additional advantage of removing a significant quantity of minerals without dissolution in the first step and also reduces the consumption of citric acid used in the demineralization step resulting in reduction in the emission of carbon dioxide. In addition, the glycerol can be used again for three successive cycles of treatment and beyond that can be recovered with charcoal treatment (90% recovery) and used again. The present method offers distinct advantages over the chemical method, such as lower residual protein (0.24%) and higher crystallinity index (80.9%) of chitin in addition to the separation of nanofibers of chitin. The recovery of byproducts, glycerol, and the simplicity of the present method guarantee that it could be a greener alternative to the chemical method, predominant in the current industrial scale production of chitin.