Abstract
It has previously been shown that the biosynthesis of the mycotoxins ochratoxin A and B and of citrinin by Penicillium is regulated by light. However, not only the biosynthesis of these mycotoxins, but also the molecules themselves are strongly affected by light of certain wavelengths. The white light and blue light of 470 and 455 nm are especially able to degrade ochratoxin A, ochratoxin B and citrinin after exposure for a certain time. After the same treatment of the secondary metabolites with red (627 nm), yellow (590 nm) or green (530 nm) light or in the dark, almost no degradation occurred during that time indicating the blue light as the responsible part of the spectrum. The two derivatives of ochratoxin (A and B) are degraded to certain definitive degradation products which were characterized by HPLC-FLD-FTMS. The degradation products of ochratoxin A and B did no longer contain phenylalanine however were still chlorinated in the case of ochratoxin A. Citrinin is completely degraded by blue light. A fluorescent band was no longer visible after detection by TLC suggesting a higher sensitivity and apparently greater absorbance of energy by citrinin. The fact that especially blue light degrades the three secondary metabolites is apparently attributed to the absorption spectra of the metabolites which all have an optimum in the short wave length range. The absorption range of citrinin is, in particular, broader and includes the wave length of blue light. In wheat, which was contaminated with an ochratoxin A producing culture of Penicillium verrucosum and treated with blue light after a pre-incubation by the fungus, the concentration of the preformed ochratoxin A reduced by roughly 50% compared to the control and differed by > 90% compared to the sample incubated further in the dark. This indicates that the light degrading effect is also exerted in vivo, e.g., on food surfaces. The biological consequences of the light instability of the toxins are discussed.
Highlights
Ochratoxin A is a toxic secondary metabolite produced by certain fungal species
To analyze if light has an influence on the stability of the secondary metabolites ochratoxin A/B or citrinin, methanolic solutions of these toxins were placed into white light (366 μW/cm2) and incubated for 24 h
The production of ochratoxin A is strongly reduced under light, especially blue light, whereas the biosynthesis of citrinin is increased under these conditions
Summary
Ochratoxin A is a composite mycotoxin with dihydroisocoumarin as the polyketide moiety coupled via peptide linkage to the amino acid phenylalanine. Ochratoxin A is chlorinated at position 5 within the dihydroisocoumarin moiety [1]. In contrast ochratoxin B has the same structure except that it does not contain chlorine but hydrogen at that position instead [1]. Like ochratoxin citrinin belongs to the benzopyrancarbonic acids and has a polyketide structure. The structure is very similar to the polyketide part of ochratoxin, but citrinin does not contain chlorine [3]. Both mycotoxins are mainly nephrotoxic and ochratoxin A is rated by the WHO/FAO as a type II carcinogen [4]. Ochratoxin A and citrinin may occur in the same food commodity [5] and may act synergistically [6] under a toxicological point of view
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