Isolation and identification of antimicrobial furocoumarins from parsley

Photoactive furocoumarins extracted from four varieties of fresh and freeze-dried parsley leaves inhibited a DNA repair-deficient Escherichia coli in a photobiological assay. Using media-modified assays, the human pathogens E. coli O157:117 and Listeria monocytogenes, the spoilage microorganism Erwinia carotovora, and Listeria innocua were also inhibited. Pseudomonas fragi was not inhibited. Minimum concentrations of Forest Green parsley powder in agar which showed inhibition ranged from 0.12% to 8.0% depending on the microorganism. Ultraviolet light (UV) at 365 nm for 60 min used to photoactivate the furocoumarins in the bioassay had little effect on L. monocytogenes and L. innocua. A slight UV inhibitory effect was detected with E. carotovora. Furocoumarins, psoralen, 8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP), oxypeucedanin and isopimpinellin were identified using gas chromatography-mass spectrometry. Psoralen, 8-MOP, and 5-MOP were quantified. A difference in relative furocoumarin concentration (weight of furocoumarin per weight of dry parsley leaves) for all varieties of parsley was revealed. The concentration of 5-MOP was significantly greater than 8-MOP (P <0.05), but not significantly greater than psoralen. Psoralen and g-MOP were not significantly different in concentration.