Enhancing physical properties and antimicrobial activity of konjac glucomannan edible films by incorporating chitosan and nisin

Abstract

The antimicrobial effect of konjac glucomannan (KGM) edible ûlm incorporating chitosan (CHI) and nisin at various ratios or concentrations was studied. This activity was tested against pathogenic bacteria, namely, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus. Mechanical and physical properties were determined, and the results indicated that the blend film KC2 (mixing ratio KGM 80/CHI 20) showed the maximum tensile strength (102.8 ± 3.8 MPa) and good transparency, water solubility, and water vapor transmission ratio. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the structural change of the blend films; and the results showed that strong intermolecular hydrogen bonds occurred between CHI and KGM. Incorporation of nisin at 463 IU per disk of film for the selected KC2 was found to have antimicrobial activity against S. aureus, L. monocytogenes, and B. cereus. The mean value of inhibition zone diameter of the CHI-N series and the KC2-N series were higher than the KGM-N series at each corresponding concentration and with significant difference (P < 0.05), however, there was no significant difference in the antimicrobial effect between CHI and KC2 incorporating nisin. At all these levels, the blend ûlm KC2-nisin had a satisfactory appearance, mechanical and physical properties, and antmicrobial activity. Therefore, it could be considered as a potential "active" packaging material. © 2006 Institute of Food Technologists.