A SELECTIVE PHOTOBIOLOGICAL ASSAY TO DETECT AND QUANTIFY PSORALEN IN PSORALEA PLANTS (LEGUMINOSAE)

A simple and rapid bioassay involving the gram-positive bacterium Baci llus brevis was developed to detect and quantify furocoumarins (psoral en and angelicin) in Psoralea plants (Leguminosae). Small paper discs, soaked with furocoumarin standards or the corresponding plant samples , are placed on B. brevis lawns in Petri dishes and irradiated for 24 h with UVA. The diameter of the growth inhibition zone around the disc s is very well-correlated with the quantity of furocoumarin standard i n the disc. Because psoralen is more phototoxic than angelicin, its de tection limit (5 x 10(-8) g/disc) was lower than angelicin (5 x 10(-7) g/disc). Consequently, it is possible to dilute a crude plant extract in order to reach a detectable psoralen concentration whilst maintain ing the angelicin concentration below its lower detection limit. In th is condition, angelicin does not interfer with psoralen detection, and the growth inhibition is entirely due to psoralen. The bioassay was v alidated using a classical high pressure liquid chromatographic method and the correlation between the two techniques was satisfactory with plant samples. Therefore, the bioassay can be considered as a sensitiv e, simple, rapid and selective method to quantify psoralen in Psoralea plants.