Evaluation of two antimicrobial packaging films against Escherichia coli O157:H7 strains in vitro and during storage of a spanish ripened sheep cheese (zamorano)

P. 296-302Entidades financiadoras: Junta de Castilla y León (Ayuda Grupo de Excelencia GR155 y Proyecto de Investigación LE331A12-2). Proyecto de Investigación AGL2011-26118/ALI. The antimicrobial activity of two packaging films (polypropylene –PP- and polyethylene terephthalate –PET-) coated with different concentrations (0, 4, 6 and 8%) of essential oil from Origanum vulgare (OR) and Ethyl Lauroyl Arginate HCl (LAE) was tested against two E. coli O157:H7 strains using in vitro systems and a raw milk sheep cheese model (Zamorano). The influence of the antimicrobials on the sensory attributes of cheese was also evaluated. For both strains, the MBC (minimum bactericidal concentration) values were identical to their respective MIC (minimum inhibitory concentration) values and lower for LAE (25 mg/l) than for OR (200-400 mg/l). PP and PET films coated with OR were tested by a vapour phase assay and the Japanish Standard method (JIS Z 2801:2000). Both films coated with LAE were tested by an agar diffusion method. Overall, in vitro tests were effective against both strains. The inhibitory activity depended on the active compound concentration, the target strain and the packaging material, PET being more effective than PP. For inoculated cheese slices, OR and LAE PP films did not effectively decrease E. coli O157:H7 counts after 7-days cold storage. PET films incorporating 6 and 8 % of OR and LAE significantly (p 0.05) affect sensorial characteristics of Zamorano cheese. Packaging with PET films coated with 6% LAE concentrations might be useful in reducing E. coli O157:H7 numbers in sheep chees