Separation of chitosan oligosaccharides by precipitation adding hydrochloric acid

Abstract

It is difficult to separate and recover chitosan oligosaccharides (COS) by the degree of polymerization (DP) or by the narrow range of molecular weights in an industrial large-scale. COS solution was precipitated by adding hydrochloric acid (HCl) at a final concentration of 2 M to 12 M. After the suspension was filtrated and its precipitate was dissolved by pure water, the dissolved precipitate and the filtrated solution were concentrated to dryness. They were dissolved again, adjusted at pH 4, lyophilized respectively, and then the precipitated fraction and the liquid fractions were obtained. In the precipitated fraction of 10% COS solution obtained by final concentration of HCl at 2 M to 4 M HCl included abundant COS DP8-DP10 (Weight-average molecular weight, Mw of precipitated fraction: 5,200-5,600). In the liquid fraction of 10% COS solution obtained by final concentration of HCl at 4 M to 6 M included abundant COS DP4-DP6. These results suggest that HCl precipitation of COS solution is a useful preparative method that can easily separate a large amount of COS by molecular weight.