Variation in Properties of Chitosan Prepared at Different Alkali Concentrations from Squid Pen and Shrimp Shell

Chitin from squid pen (Loligo sp.) and kiddi shrimp shell (Parapenaeopsis stylifera) were treated at room temperature (30 +/- 2 degrees C) with four different concentrations of sodium hydroxide: 20, 30, 40, and 50%w/w. With 50% sodium hydroxide solution, within 108h, the chitin from squid pen was deacetylated to give chitosan. But it required 126h at 40% and 144h at 30% concentration of sodium hydroxide. In the case of chitin from Parapenaeopsis stylifera, complete deacetylation took place after 120h and 168h at 50 and 40% concentrations of sodium hydroxide, respectively. But shrimp shell on treatment with 20 and 30% sodium hydroxide solutions and squid pen kept at 20% sodium hydroxide were not sufficiently deacetylated even after 480h. Properties like degree of deacetylation, viscosity and molecular weight of the prepared chitosan samples were studied. Minimum alkali concentration required for the formation of chitosan at room temperature was found to be 30% for squid chitin and 40% for shrimp chitin. With the increase in the time of deacetylation, decreases in molecular weight and viscosity were observed in chitosan from both sources. Maximum viscosity was recorded by chitosan prepared from squid pen using 30% sodium hydroxide solution at room temperature.