Antimcriobial Activity and Mechanism of Chitosan with Different Molecular Weight

Ten different molecular weights chitosan (range from 5.5×104 Da to 15.5×104 Da) with the same degree of deacetylation (DDA) were obtained by the method of acetic acid hydrolyzing. Chitosans were characterized by Fourier transform infrared spectroscopy (FTIR). The effect of antibacterial activities of chitosans was explored by the methods of optical density and counting the colony forming unit (CFU). The middle molecular weights chitosan (range from 8.8×104 Da to 9.0×104 Da) have higher activities than high molecular weight (15.5×104 Da) and low molecular weight chitosans (5.5×104 Da). All the chitosan at the concentration from 0.005% to 0.01% have better antibacterial activity than at the concentration from 0.001% to 0.002% and from 0.02% to 0.05%. The antimicrobial mechanism was presumed that chitosan bind to the outer member of the spoilage yeast to cause surface of the yeast altering and flocculating.