Structural differences between chitin and chitosan extracted from three different marine sources

Three marine sources of chitin from Tunisia were investigated. Structural differences between a-chitin from shrimp (Penaeus kerathurus) waste, crab (Carcinus mediterraneus) shells, and beta-chitin from cuttlefish (Sepia officinalis) bones were studied by the C-13 NMR, FTIR, and XRD diffractograms. The C-13 NMR analysis showed a splitting of the C3 and C5 carbon signals for alpha-chitin, while that of beta-chitin was merged into a single resonance. The bands contour of deconvoluted and curve-fit FTIR spectra showed a more detailed structure of a-chitin in the region of O-H, N-H and CO stretching regions. IR and C-13 NMR were used to determine the chitin degree of acetylation (DA). XRD analysis indicated that alpha-chitins were more crystalline polymorph than beta-chitin. Shrimp chitin was obtained with a good yield (20% on raw material dry weight) and no residual protein and salts. Chitosans, with a DA lower than 20% and relatively low molecular masses were prepared from the wet chitins in the same experimental conditions. They were perfectly soluble in acidic medium. Nevertheless, chitin and chitosan characteristics were depending upon the chitin source. (c) 2014 Elsevier B.V. All rights reserved.