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 mu g/ml, 5-MOP, 1,634 +/- 62 mu g/ml, and 8-MOP, 44 +/- 2 mu g/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 W 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 mu g/g and the minimum bactericidal concentration was 43 mu g/g. Cold-pressed lime oil inhibited L. monocytogenes even at the lowest concentration added to the model system (10 mu g/g), while the corresponding LF standard did not. This suggested the presence of other antimicrobial agents in the oil.