Extraction and Characterization of Chitosan from Crab and Periwinkle Shells

Abstract

Chitosan is a biopolymer obtained by deacetylating chitin and is commonly produced from crustacean shell waste. This study compared the extraction and characterisation of chitosan from crab (Callinectes amnicola) and periwinkle (Tympanotonus fuscatus) shells under identical chemical conditions. The shell powders were subjected to demineralisation with 1.25 M HCl, deproteinisation with 2.5% NaOH, and deacetylation with 25% NaOH. The products were assessed for percentage yield, degree of deacetylation (DDA) by potentiometric titration, solubility, and functional groups by Fourier-transform infrared spectroscopy. Crab shells produced a chitosan yield of 18.4% and a DDA of 80.3%. The corresponding FTIR spectrum showed characteristic amine and polysaccharide bands and no residual carbonate peaks, indicating effective demineralisation and deacetylation. In contrast, periwinkle shells produced a lower yield of 10.9%, while the resulting product had a DDA of <10% and poor solubility. Its FTIR spectrum showed strong carbonate bands and an absence of characteristic amine bands, indicating incomplete demineralisation and deacetylation. The periwinkle-derived product was therefore predominantly chitin rather than chitosan under the applied conditions. These findings show that identical processing conditions do not yield equivalent products from crustacean and molluscan shell matrices. Source-specific optimisation, particularly more intensive demineralisation and deacetylation for periwinkle shells, is required to improve conversion to chitosan.