Influence of manufacturing variables on the characteristics and effectiveness of chitosan products. I. Chemical composition,viscosity, and molecular-weight distribution of chitosan products

Ten chitosan products were manufactured from dry shrimp hulls under differing process conditions and compared to a commercially available product. Manufacturing variables tested were: alkali versus enzymatic deproteination; acid demineralization versus no treatment; air versus nitrogen atmosphere; 5 min vs. 15 min deacetylation period: and varying the particle size of the dry starting material. Deproteination by alkali of enzymatic extraction did not substantially affect the nitrogen and ash compositions of dry chitosan samples. However, the viscosity was reduced in samples deproteinated by enzymatic hydrolysis. Elimination of the demineralization step resulted in products having 31–36% ash, as expected. Some differences in viscosity were observed between deminiralized and undemineralized samples, but on important differences in the molecular-weight distribution of these samples were evident. Purging the reaction vessel with nitrogen resulted in chitosan preparations having higher viscosities and molecular-weight distributions than those prepared in an air atmosphere. The degradative effect of air became more proshrimp hulls to 1 mm prior to any treatment resulted in a chitosan product of both higher viscosity and molecular weight than when ground to either 2 or 6.4 mm. Viscosity was not always a direct indicator of molecular weight, for although the presence of colloidal particles increased the viscosity of some samples, the molecular-weight distribution after filtration was essentially the same as in other less viscous samples.