Behaviour of Listeria monocytogenes and autochthonous flora on meat storedunder aerobic, vacuum and modified atmosphere packaging conditions with orwithout the presence of oregano essential oil at 5 degrees C

The effect of aerobic, modified atmosphere packaging (MAP; 40% CO2/30% O-2/ 30% N-2) and vacuum packaging (VP) on the growth/survival of Listeria monoc ytogenes on sterile and naturally contaminated beef meat fillets was studie d in relation to film permeability and oregano essential oil. The dominant micro-organism(s) and the effect of the endogenous flora on the growth/surv ival 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 th e pathogen. Brochothrix thermosphacta constituted the major proportion of t he total microflora in MAP/VP within the low-permeability film, where no gr owth of L. monocytogenes was detected either on naturally contaminated or s terile meat fillets. The addition of 0.8% (v/w) oregano essential oil resul ted in: (i) an initial reduction of 2-3 log(10) of the majority of the bact erial population, with lactic acid bacteria and L. monocytogenes indicating the most apparent decrease in all gaseous environments, and (ii) limited g rowth aerobically and survival/death of L. monocytogenes in MAP/VP, regardl ess of film permeability.