Properties and antimicrobial activity of edible films incorporated with kiam wood (Cotyleobium lanceotatum) extract

The antimicrobial properties of wood extracts are well known; however their application to edible films is limited. In this study, the minimum bactericidal concentration (MBC) of kiam wood extract was established as 300 mg/L at which bacterial growth was completely inhibited. The antimicrobial properties of hydroxypropyl methylcellulose (HPMC) films containing 1-5 fold of MBC of kiam wood extract were tested against Escherichia coli O175:H7, Staphylococcus aureus and Listeria monocytogenes. The edible films containing kiam wood extract exhibited more effective impact on the growth reduction of L monocytogenes than S. aureus and E. coli (p < 0.05). The use of kiam wood extract at 1 and 2 fold of MBC incorporated into edible HPMC films did not exhibit any antimicrobial activity. However, the inhibitory effect of edible HPMC films containing kiam wood extract was observed at 3, 4 and 5 fold of MBC. The greatest zone of inhibition was observed at 5 fold of MBC incorporated in edible HPMC films. Tensile strength and elongation at break significantly decreased with the incorporation of kiam wood extract, whereas water vapor permeability and film solubility increased. The color of edible films became darker and more reddish-yellowish as well as having a lower transparency as the level of kiam wood extract was increased. Kiam wood extract incorporated in edible film provided the films with a rougher surface than pure edible film. Our results pointed out that the incorporation of kiam wood extract as a natural antibacterial agent has potential for use in extending the shelf life of food products. (C) 2010 Elsevier Ltd. All rights reserved.