Inhibition of Listeria monocytogenes, Escherichia coli O157:H7, and Micrococcus luteus by linear furanocoumarins in a model food system

Abstract

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.