Behaviour of Listeria monocytogenes and autochthonous flora on meat stored under aerobic, vacuum and modified atmosphere packaging conditions with or without the presence of oregano essential oil at 5 degrees C.

The effect of aerobic, modified atmosphere packaging (MAP; 40% CO2/30% O2/30% N2) and vacuum packaging (VP) on the growth/survival of Listeria monocytogenes on sterile and naturally contaminated beef meat fillets was studied in relation to film permeability and oregano essential oil. The dominant micro-organism(s) and the effect of the endogenous flora on the growth/survival of L. monocytogenes were dependent on the type of packaging film. The fact that L. monocytogenes increased whenever pseudomonads dominated, i.e. aerobic storage and MAP/VP in high-permeability film, and even earlier than on sterile tissue, suggests that this spoilage group enhanced growth of the pathogen. Brochothrix thermosphacta constituted the major proportion of the total microflora in MAP/VP within the low-permeability film, where no growth of L. monocytogenes was detected either on naturally contaminated or sterile meat fillets. The addition of 0.8% (v/w) oregano essential oil resulted in: (i) an initial reduction of 2-3 log10 of the majority of the bacterial population, with lactic acid bacteria and L. monocytogenes indicating the most apparent decrease in all gaseous environments, and (ii) limited growth aerobically and survival/death of L. monocytogenes in MAP/VP, regardless of film permeability.