Antimicrobial Effects of Mentha pulegium Essential Oil on Listeria monocytogenes in Iranian White Cheese

Background: Listeria monocytogenes is an important Gram-positive disease-causing bacterium existing in milk and dairy products. Inhibitory effects of Mentha pulegium essential oil at concentrations of 0.03, 0.015, and 0.0075% on growth of L. monocytogenes were studied in Iranian white cheese during 60 days of storage. Methods: Essential oil of M. pulegium plant, collected from north of Iran, was extracted by Clevenger apparatus and analyzed by gas chromatography mass spectrometry (GC-MS). The antibacterial effects of the oil were evaluated by growth of the microorganism in control and treatment cheese samples. Also, sensory properties of the cheese samples containing different concentration of M. pulegium were determined. Statistical analyses were performed by ANOVA and Fisher&rsquo;s Least Significant Difference (LSD) procedure using SPSS 16.0 software. Results: GC/MS analysis showed that the major compounds of M. pulegium essential oil were pulegone (36.68%), piperitenone (16.88%) and 1,8 cineole (14.58%). In control group, L. monocytogenes grew in 7 days and then their growth decreased gradually during 60 days. But, in all treated samples there is a log reduction in bacterium count while the maximum growth lasted for 14 days with a significant difference (p<0.05) compared with control samples. Although 0.03% concentration of mentha oil had the most strong antibacterial effects, but the samples with 0.015% essential oil had significantly higher organoleptic properties score comparing the other samples (p<0.05). Conclusion: M. pulegium essential oil not only can improve organoleptic properties of cheese but also can reduce and postpone the growth of L. monocytogenes in this product.