Characterization of the effects on the growth kinetics of Listeria monocytogenes in solid culture in contact with caseinate base edible films added with antilisterial activity from Streptococcus sp. ABMX isolated from Pozol, an indigenous Mexican beverage

The antilisterial activity of edible films that contained 4% w/v sodium caseinate, 30% w/v glycerol, dry-based, and different amounts of antimicrobial substances (AM) produced by Streptococcus sp. ABMX, a lactic acid bacterium isolated from Mexican Pozol, was characterised. The AM were incorporated into the films as concentrated supernatant of culture broths, giving concentrations expressed as gentamicin, for the control-film, treatment 1 (T1), T2, T3 and T4 of 0, 0.5, 0.7, 0.9 and 1.25 mg_gentamicin/g_film, respectively. Listeria monocytogenes was grown in Oxford agar in contact with the tested films, at 35°C during 72 h, rendering the following ranges for the colony growth kinetic parameters: 19<colony lag phase, λ_c (h)<∞; 0<maximum specific colony growth rate, μ_c-max(h^-1)<0.74, and 0 < maximum biomass accumulation [proportional to the maximum value (colony growth area at any time)/(initial colony growth area) = (A/A0)max (dimensionless)]<460. There were important differences among treatments, being the L. monocytogenes growth more affected as the AM concentration increased within the films. Best antilisterial results were obtained in T4 condition, where L. monocytogenes could not grow.