Physicochemical, Functional and Spectroscopic Analysis of Crawfish Chitin and Chitosan as Affected by Process Modification.

Traditional isolation of chitin from crawfish shells involves three sequential steps: demineralization (DM, removing calcium carbonate/phosphate), deproteinization (DP), and decolorization (DC, removing mainly astaxanthin). The first two steps can be reversed (i.e., DMP or DPM). Chitin is converted to chitosan by deacetylation (DA). Isolation steps may be shortened, depending on intended applications of chitosan. The first study investigated effects of (1) reversing sequence and (2) eliminating DP and DC steps on physicochemical and functional properties of chitosan and conversion efficiency of chitin. Twelve different processes: DM, DP, DPM, DMP, DPMC, DMPC, DMA, DMCA, DPMA, DMPA, DPMCA, DMPCA were investigated. DA of DPMC did not affect bulk density. Without DP and DC, bulk density of chitosan significantly increased. Nitrogen content of DMA-chitosan was 6.96% compared to 7.4--7.9% of commercial crab chitosans. DA removed 19% protein from demineralized shells. Deproteinized and demineralized shell once dried was not an effective substrate for decolorization. The conversion efficiency (CEF) of demineralized shell to non-deproteinized/non-decolorized chitosan (DMA) was 52.5%. The Water Binding Capacity (WBC) and Fat Binding Capacity (FBC) of the crawfish chitins were compared with those of commercial chitin and chitosans. This study shows that isolation steps for chitosan production can be reduced, which, in turn, would lower production cost and produce less chemical wastes compared to the traditional process. Several methods are available for determining (Degree of Deacetylation) DD, including NMR, linear potentiometric titration, ninhydrin test, and first derivative UV-spectrophotometry. The second study was aimed to develop the method to determine DD and purity of crawfish chitin and chitosan using FTIR spectroscopy. Chitin and chitosan with various DD were finely ground (0.5mm), oven-dried at 95°C, and analyzed for DD and purity using FTIR spectroscopy. The spectral region of 1200--1800 cm-1 was the information rich-region. DD of chitosan was estimated using the ratio of absorption at 1655 and 3450 cm-1 . Chitosan with DD of 75, 80, 85 and 91 showed similar FTIR spectra pattern. The FTIR spectroscopy may serve as a rapid method to determine DD and purity of chitosan