Cellulase degradation of shrimp chitosan for the preparation of a water-soluble hydrolysate with immunoactivity

Abstract

Samples of colloidal chitin and chitosans with deacetylation degrees (DD) of 50, 65, 75 and 95% (DD50, DD65, DD75 and DD95, respectively) were prepared from shrimp chitin. The hydrolytic activity of cellulase on these samples increased with the increasing DD of chitosan, with DD95 being the most easily hydrolyzed. Colloidal chitin was hardly hydrolyzed. The optimal reaction temperature and pH for cellulase digestion of chitosan were 55°C and pH 5.2, respectively. During cellulase digestion of chitosan, the 9-h hydrolysate had the highest enhancing effect on the proliferation of a human hybridoma cell, HB4C5. This hydrolysate is composed of low-molecular-weight chitosan (LMWC), with a molecular mass of 20.0 kDa, and chitooligosaccharides, which are composed of sugars with a degree of polymerization of 1-6. In vitro, the 9-h hydrolysate increased both cell proliferation and immunoglobulin (Ig) M secretion of HB4C5 because of the presence of chitooligosaccharides for the former activity and LMWC for the latter activity. In vivo, samples of the chitosan hydrolysate, chitooligosaccharide mixture and LMWC significantly increased the levels of serum IgG and IgM, and enhanced concanavalin A- and lipopolysaccharide-induced proliferation of mouse lymphocytes.