Inhibition of Listeria monocytogenes , Escherichia coli O157:H7, and Micrococcus luteus by Linear Furanocoumarins in a Model Food System.

Lime peel, parsnip, lemon peel, dried parsley flakes, cold pressed lime oil, and distilled lime oil samples were analyzed for the presence and concentration of the linear furanocoumarins (LFs) psoralen, 5-methoxypsoralen (5- MOP), and 8-methoxypsoralen (8-MOP) by thin layer chromatography and gas chromatography mass spectrometry. Cold-pressed lime oil had the highest LF content (psoralen, 67 ± 29 µg/ml, 5-MOP, 1,634 ± 62 µg/ml, and 8-MOP, 44 ± 2 µg/ml). The antimicrobial effectiveness of LFs against Listeria monocytogenes , Escherichia coli O157:H7, and Micrococcus luteus was tested in a model food system consisting of a slurry of 25% commercial "garden vegetables" baby food in 0.1% peptone water. Inhibition required UV activation after the addition of the LFs to the model system. Lime peel extract, cold-pressed lime oil, and a 5-MOP standard inhibited the growth of L. monocytogenes , but not E. coli O157:H7. M. luteus was inhibited only by the cold-pressed lime oil. The minimum LF concentration that caused inhibition of the growth of L. monocytogenes was 32 µg/g and the minimum bactericidal concentration was 43 µg/g. Cold-pressed lime oil inhibited L. monocytogenes even at the lowest concentration added to the model system (10 µg/g), while the corresponding LF standard did not. This suggested the presence of other antimicrobial agents in the oil.

Inhibition of Listeria monocytogenes , Escherichia coli O157:H7, and Micrococcus luteus by Linear Furanocoumarins in Culture Media.

The linear furanocoumarins psoralen, 5-methoxypsoralen (5-MOP), and 8-methoxypsoralen (8-MOP) were tested as antimicrobial agents against Listeria monocytogenes , Escherichia coli O157:H7 and Micrococcus luteus . The linear furanocoumarins were activated with UV light at 365 nm for 60 min. MICs of these furanocoumarins in tryptic soy broth supplemented with 0.6% yeast extract were determined at room temperature for 48 h. Psoralen was the most effective antimicrobial agent of the three studied. This compound inhibited the three test microorganisms at concentrations of 5 µg/ml or lower. Only L. monocytogenes was inhibited by 5-MOP.Concentrations of at least 10µg of 8-MOP per ml were required to inhibit the test microorganisms. Mixtures containing at least 7.5 µg of psoralen per ml inhibited the growth of the three microorganisms. In the absence of psoralen, mixtures of 5- MOP and 8-MOP were ineffective as growth inhibitors of M. luteus and E. coli O157:H7.