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Productions of Chitin and Valuable Substances from Crab Shell Using Sub-Critical Water

Hiroyuki Yoshida, Hidemi Nakamura, Norihisa Nakai, and Hiroki Oozono. Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, 599-8531, Japan

Efficient method for production of chitin and useful substances from crab shell using sub-critical water treatment was proposed. In the conventional producing method of chitin, it was able to be confirmed that crab shell contains protein (25%), calcium carbonate (40%), chitin (35%), some pigments and lipids. We found that the sub-critical water decomposed the protein and pigments, and removed them rapidly and completely under the conditions of reaction temperature of 533 - 593K and reaction time of 1 - 20 min. The sub-critical water also extracts lipids completely from crab shell. However, most of calcium carbonate were not decomposed and removed. The residual solid decreased with reaction temperature and became to 75 % (533 K), 65 % (563 K) and 53 % (599 K) of initial weight of crab shell. Since the residual calcium carbonate was removed by additional treatment of 2 N aqueous HCl solution for two days, this two stage method is also useful for new chitin producing method compared to the conventional method with many processes, long time treatment and large cost. In the aqueous phase, various useful organic acids such as acetic acid and pyroglutamic acid, and amino acids such as alanine and arginine were produced by the hydrolysis reaction of protein in the crab shell. This reaction was very fast, and the yields of produced amino acids and organic acids are dependent on reaction time and temperature. In addition, by the sub-critical water treatment in further high temperature of 593K - 623 K, a part of the chitin was decomposed. Decomposition products were oligosaccharides, glucosamine and erythrose, etc. It was clarified that this sub-critical water treatment method was useful as a saccharic manufacturing method of low molecular weight from the chitin.