Fresh minced meat was artificially contaminated with Listeria monocytogenes
and subjected to different treatments; 0.25% oregano essential oil (OEO); 0.5% OEO;
1 % OEO; modified atmosphere packaging (MAP); combination of 0.25% OEO+ MAP;
0.50% OEO+ MAP and finally 1% OEO+ MAP to study the effect of these treatments
on Listeria monocytogenes and on shelf life of minced meat stored at 5°C. The initial
contamination level of Listeria monocytogenes on minced meat was 3.64 log,o cfu/g. It
was seemed that a reduction of 0.36. 0.95 and 1.52 10g1O CFU/g units were obtained
by the treatments with 0.?5% OEO. 0.50% OEO and 1%OEO. respectively. This
antimicrobial effect. increased with increasing concentration of OEO On day 4 there
was a Significant difference (P<0.05) for the number of Listeria monocytogenes
between the control and all the treatments. After 17 days of storage at 5 °C the log,o
CFU/g of Listeria monocytogenes on minced meat treated with MAP+1%OEO was still
lower by 2.97 units as compared with" Ie initial number. Results revealed that the total
viable count; Enterobacteriaceae and Listeria monocytogenes were inhibited by all
treatments used as compared with the untreated sample. Sensory evaluation revealed
that the presence of essential oil contributed to the maintenance of visual appearance
of minced meat for long time. The addition of 0.25; 0.5 and 1 % oregano essential oil
(OEO) to samples packed in MAP affected positively the odour and the colour of the
minced meat. Microbiological changes supported the sensory results. Minced meat
treated with 0.5% oregano essential (OEO); 1% OEO; Modified Atmosphere
Packaging (MAP); 0.25% OEO + MAP; 0.5% OEO+ MAP and 1% OEO + MAP
showed a shelf life at 5°C of 5. 6.11.12. 14 and 17 days respectively. This Signifies a
prolongation of shelf life at 5°C of 1. 2. 7. 8. 10 and 13 days respectively, as
compared with control samples. The antimicrobial effect increased with increasing
concentration of OEO. The best results were obtained by treating minced meat with
1% OEO combined with MAP (85% C02+10% 02). Apparently, a synergistic activity
between the oregano essential oil (OEO) and the modified atmosphere packaging
(MAP) is involved.