The physical properties and antimicrobial activitiesagainst Listeria monocytogenes of the tapioca starch/decolorized hsian-tsao leaf gum (the polysaccharide gumextracted from hsian-tsao herb followed by removing thecolor matters, abbreviated as dHG hereafter)-based filmsincorporated with potassium sorbate (KS) or the ethanolicextract of thyme (TH) were investigated. It was found thatthe cross-sectional microstructure of starch/dHG films withKS showed some rough texture, and films with TH showed arelatively smooth microstructure with dispersed microparticles.The equilibrium moisture content and water vaporpermeability of starch/dHG films with 20 % KS (based onthe weight of starch/dHG) was higher than the others tested,possibly due to the plasticizing effect of KS. In general, thetensile strength and tensile modulus decreased with increasingantibacterial concentration. As compared with the KS solutions,the TH solutions showed a pronounced antimicrobialactivity against L. monocytogenes as determined by the inhibitionzone test. However, the antimicrobial migration of bothKS and TH in the starch/dHG matrix was limited to a certainextent, as evidenced by the significantly lower antimicrobialactivity in the film system. When applying the starch/dHGfilms with antimicrobials to the fresh beef slices, all samplesshowed detectable improvement against the growth of L.monocytogenes, implying that starch/dHG films incorporatedwith TH or KS were effective against L. monocytogenes inconjunction with some modification of the physical propertiesdue to the interactions between the antimicrobials and thecomponents of film matrix
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