Effects of Food Components on the Antibacterial Activity of Chitosan against Escherichia coli

The antibacterial activity of chitosan against Escherichia coli was investigated in the presence of NaCl, sucrose, and ethanol to assess the potential use of chitosan as a biopreservative in food products containing these components. The inhibitory activity of chitosan decreased slightly upon the addition of NaCl and sucrose, respectively to culture broth containing 100 ppm of chitosan (Mw 3,000), while the addition of ethanol enhanced the inhibitory activity of chitosan on growing cells. The addition of these components to non-growing cells prior to chitosan treatment demonstrated that NaCl protected the cells from the inhibitory activity of chitosan, while sucrose had no effect. Ethanol addition to non-growing cells increased cell death by chitosan treatment. Finally, binding of fluorescein isothiocyanate (FITC)-labeled chitosan to E. coli was measured in the presence of the food components. The FITC-labeled chitosan binding to cells decreased upon NaCl addition, was not affected by sucrose, and increased following treatment with ethanol.