Antimicrobial Polylactic Acid Packaging Films against Listeria and Salmonella in Culture Medium and on Ready-to-Eat Meat

The contamination of Listeria monocytogenes and Salmonella spp. in ready-to-eat (RTE) meat products has been a concern for the meat industry. In this study, edible chitosan-acid solutions incorporating lauric arginate ester (LAE), sodium lactate (NaL), and sorbic acid (SA) alone or in combinations were developed and coated on polylactic acid (PLA) packaging films. Antimicrobial effects of coated PLA films on the growth of Listeria innocua, L. monocytogenes, and Salmonella Typhimurium in a culture medium (tryptic soy broth, TSB) and on the surface of meat samples were investigated. Antimicrobial PLA films containing 1.94 mg/cm(2) of chitosan and 1.94 mu g/cm(2) of LAE were the most effective against both Listeria and Salmonella in TSB and reduced them to undetectable level (<0.69 log CFU/ml). The same PLA films with LAE significantly (p<0.05) reduced the growth of L. innocua, L. monocytogenes, and S. Typhimurium on RTE meat during 3 and 5 weeks' storage at 10 degrees C, achieving 2-3 log reduction of Listeria and 1-1.5 log reduction of Salmonella as compared with controls. PLA films coated with 1.94 mg/cm(2) of chitosan, 0.78 mg/cm(2) of NaL, and 0.12 mg/cm(2) of SA significantly reduced the growth of L. innocua but were less effective against Salmonella. The combination of NaL (0.78 mg/cm(2)) and SA (0.12 mg/cm(2)) with LAE (1.94 mu g/cm(2)) did not generate additional or synergetic antimicrobial effect against Listeria or Salmonella on the meat surface. L. innocua had a similar sensitivity to the film treatments as L. monocytogenes, suggesting that L. innocua may be used as a surrogate of L. monocytogenes for further scaleup and validation studies. The film treatments were more effective against the microorganisms in TSB culture medium than in RTE meat, which suggests that in vivo studies are a necessary step to develop antimicrobial packaging for applications in foods.