Effects of MolecularWeight and Concentration of Chitosan on Antifungal Activity Against Aspergillus Niger

The antifungal activities of chitosan with different molecular weights and concentrationsagainst Aspergillus niger were studied in vitro. The results showed that the antifungal activity of chitosan against Aspergillus niger is molecular weight and concentration dependent. The smaller the molecular weight, the stronger would be the antifungal activity. Chitosan with higher molecular weight and concentration has no antifungal but promotion activity towards Aspergillus niger. It is only the chitosan with proper molecular weight and concentration which possesses preferable antifungal activity towards Aspergillus niger. The effects of chitosan on Aspergillus niger and hyphal ultrastructure were examined to gain more information on its mode of action. The ultrastructure morphology investigated by transmission electron microscopy results indicated that chitosan acts on Aspergillus niger by inhibiting the growth of sporules. The fluorescein isothiocyanate labelled chitosan observation has elucidated the antifungal activity of chitosan to be caused mainly by inhibiting the DNA to RNA transcription. So the antifungal activity of chitosan towards Aspergillus niger was the combined effect of the above two observations. The study has provided sufficient scientific evidence for careful application of chitosan in food and medical industry.