Comparison of methods to evaluate chitosan as an antimicrobial against Listeria spp. cultures.

摘要

The antimicrobial properties of a chitosan-coated vacuum-packaged pouch were tested against Listeria monocytogenes (LM) inoculated on frankfurters. A 1.5% chitosan solution was successfully coated onto a corona-treated poly/nylon based film and then heat-sealed to form a pouch. An initial 5 log CFU/mL population of LM was used to inoculate a frankfurter in the pouch, which was then vacuum-sealed and stored at 4° and 13° C for a period of 8 weeks, with bacteria enumeration performed on weekly intervals. An uncoated pouch was tested as a control. It was found that the chitosan-coated pouches did not exhibit any antimicrobial properties against the LM in comparison to the control pouches. This serves as evidence of the inability of chitosan components to diffuse through a solid matrix, such as a film on solid media, and effectively inhibit bacteria growth. The bacteria population in the chitosan-coated pouches was between 5.5 and 7 log CFU/mL after 8 weeks of shelf life testing. This was similar to the bacteria levels in the control pouches.;Initial research compared commonly used screening tests for their ability to effectively identify or characterize antimicrobial properties of chitosan. The two outlined are Film Overlay and Shake Flask assay, which are representative of solid and liquid matrices, respectively. It was found that the Film Overlay assay is not adequate for chitosan films, as the solid matrix and hydrophilic nature of chitosan do not yield results indicative of the antimicrobial characteristics of chitosan. The chitosan film had a tendency to curl up and no zones of inhibition were present. It was determined that the liquid matrix and direct surface contact of the Shake Flask assay was critical in identifying effective antimicrobial components. The testing found that a chitosan film in a Tryptic Soy Broth/ Listeria innocua solution exhibited a 2 log CFU/mL reduction after 48 hours in comparison to the control film.