Raman spectroscopic evaluation of the influence of Pseudomonas bacteria on aflatoxin B1 in the BioArena complex bioautographic system

The mechanism of the antibacterial‐toxic effect of aflatoxin B1 (AFB1) was investigated in the BioArena complex bioautographic system that consists of planar liquid chromatographic development and biological detection. In this system, the killing‐inhibiting activity of AFB1 against Pseudomonas savastanoi (Psm) bacterial cells was visualised. The role of formaldehyde (HCHO) was suggested in the antibacterial‐toxic action of AFB1. Raman spectroscopy (RS) was used to investigate whether the excess HCHO found earlier in the AFB1 spot (comparing with background) originated partly from the demethylation of the toxin, or only from the enhanced demethylation of the normal cell ingredients because of the stress situation. Fourier transform (FT) Raman and surface‐enhanced FT‐Raman spectra were obtained in situ about the AFB1 chromatographic and background spots in bacteria‐free and inoculated thin layer chromatography (TLC) layers, and ex situ about their dried methanolic extract. The reduction of the δ CH₃ band of AFB1 (1386 cm⁻¹) in the presence of Psm can indicate the demethylation of aflatoxin at its methoxy‐group in BioArena. It seems from the Raman spectra that, apart from demethylation, aflatoxin does not suffer other structural changes. However, Psm can reduce the Raman activity of νCO bond of the pyran ring of AFB1, causing lower intensity and a broader band (1747 and 1754 cm⁻¹). Psm can also disrupt the strong interactions between the AFB1 and the adsorbent layer through the νCO bond of the cyclopentene ring causing a blue‐shift (1667 → 1686 cm⁻¹). The very reactive HCHO that originated from exogenous sources, e.g. from the demethylation of AFB1, has no determined biochemical pathway, so it means higher risk. Copyright © 2008 John Wiley & Sons, Ltd.