Alkaline N-deacetylation of chitin using a twin -screw continuous processor: Optimization and characterization of products
Chitosan is produced by the deacetylation of chitin. The objectives of this study were to optimize the deacetylation process for the production of chitosan using a twin-screw continuous processor and to characterize the products under optimization conditions. The optimization operations were done with a factorial combination of process variables: steam pressure, ratio of chitin and sodium hydroxide, solids content, and feed rate. The statistical models to predict the yields of chitosan I and chitosan II were developed. The solids content and the ratio between sodium hydroxide and chitin had significant effect on the yield of the chitosan I. For the yield of chitosan II, the ratio between sodium hydroxide and chitin had the most significant effect. Steam pressure also affected the yield of chitosan I and chitosan II. ^ The degree of deacetylation and the molecular weight of the chitosan samples produced by this method ranged from 70 to 80% and 2.7 X 10 5 to 5.1 X 105 Da, respectively. The molecular weight of chitosan II was significantly higher than that of the chitosan I. The melting temperature of the chitosan samples produced by this method ranged from 152 to 180°C and the enthalpy for the endothermic reaction ranged from 160 to 234 J/g. The solubility of chitosan in aqueous solution at various pHs was similar and had a significant correlation with the degree of deacetylation and the molecular weight. Both chitosan I and chitosan II showed a similar pattern of solubility at various pH ranges. A high temperature and a high shear process can randomize the deacetylation process, which produces chitosan products that are soluble in aqueous solution at neutral pH. The fat binding capacity, which ranged from 198 to 296%, had a significant positive correlation with the degree of deacetylation, the molecular weight, and the crystallinity and was affected by drying method.^
Li-Fu Chen, Purdue University.
Agriculture, Food Science and Technology