Abstract
A complex of chitosan (CSโ40) and nisin (CSโ40/nisin) was prepared and characterized with Fourier transform infrared spectroscopy and thermal analysis (thermogravimetry, differential thermogravimetry, and differential scanning calorimetry). The results show that the complex formed mainly by electrostatic interaction between the protonated amino group in CSโ40 backbone with the carboxylate ion of nisin. Minimum inhibitory concentrations (MICs) were evaluated against Gramโpositive bacteria (Staphylococcus aureus, Bacillus subtilis, and Bacillus stearothermophilus), Gramโnegative bacteria (Escherichia coli, Salmonella enteritidis, and Proteus vulgaris), and fungi (Fusarium oxysporum). The results show that the CSโ40/nisin solution did inhibit or even more strongly inhibited the growth of all the tested microorganisms, whereas CSโ40 did not inhibit the growth of F. oxysporum and nisin did not inhibit the growth of Gramโnegative bacteria (E. coli, S. enteritidis, and P. vulgaris). The relative inhibition times of CSโ40/nisin solutions with different concentrations and ratios of CSโ40 and nisin were also investigated against the seven microorganisms. The results showed that CSโ40/nisin solutions with CSโ40/nisin concentration ratios of 0.05/0.005, 0.05/0.0025, 0.05/0.00125, and 0.025/0.0001% had higher antimicrobial activity against all tested bacteria and fungi. The relationship between complex formation and antimicrobial activity is discussed. ยฉ 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010