Physico-chemical characterization of fungal chitosan from shiitake stipes

Fungal chitosan was prepared by alkaline N-deacetylation of crude chitin obtained from air-dried shiitake stipes. The yields of precipitated and soluble chitosans were 218.4–240.3 and 69.3–83.4 mg/g, respectively. The degrees of N-deacetylation (DD) of precipitated chitosans increased with the prolonged reaction time and reached 90.18% at 120 min. The average molecular weights (MW) of both chitosans decreased with the prolonged reaction time. The lightness and whiteness index values of precipitated chitosans were higher than those of soluble chitosans. After N-deacetylation, carbon and nitrogen contents and N/C ratios of chitosans significantly increased. The endothermic and exothermic peak temperatures of precipitated chitosans were higher than those of soluble chitosans. Two characteristic crystalline peaks for precipitated chitosans were at 2θ=9.65° and 19.87° and three WAXD patterns were similar. Under electron microscopic examination, both chitosans showed the aggregated flakes with dense and firm structure and without porosity. Generally, both chitosans prepared showed different physico-chemical characteristics as evidenced by the DD, MW, element analysis, DSC, WAXD and SEM patterns.