Chitin from fermentative extraction of crab shells using okara as a nutrient source and comparative analysis of structural differences from chemically extracted chitin

Chitin was obtained by economic fermentative and chemical extractions from crab shell to compare the structural differences. In the fermentation, soybean curd residue (okara) and its extracted protein were used as nutrient sources in the proteinic culture medium of Bacillus pumilus. It was found that essential amino acids and minerals contained in okara-extracted protein were similar to those of commercial yeast extract leading to chitin with similar properties. A comparison of biologically and chemically extracted chitins showed the degree of acetylation was ca. 71 %, but their crystallinities were different at 73 % and 86 %, respectively, the result of differences in intermolecular hydrogen bonding and crystallite size. A high degree of deproteinization of chitin was found after fermentation, while decalcification occurred to a small extent. Post-fermentation treatment with acetic acid enhanced the decalcification to nearly 100 %. The purified chitin had a weight average molecular weight of 4 - 10 x 10(6)g/mol, depending on the extraction condition.