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The complex ecology of mould growth and mycotoxin production can produce mixtures of mycotoxins in food and feed grains, particularly in cereals. The co-occurrence of mycotoxins can arise through a single mould producing more than one toxin and simultaneous contamination by two or more moulds, from the same or different species.
The co-occurrence of the Fusarium graminearum toxins deoxynivalenol and zearalenone with the F. moniliforme toxins fumonisin B1 and B2, for example, has been reported (Miller, 1991) in southern Africa. Other naturally occurring combinations of Fusarium mycotoxins include T-2/diacet-oxyscirpenol (DAS) (Figure 2.6. Chemical structures of Diacetoxyscirpenol, Fusarenone and Cyclopiazonic acid.), deoxynivalenol/DAS and DAS/fusarenone (Figure 2.6b). Naturally occurring combinations of mycotoxins produced by more than one genus include aflatoxins/trichothecenes (Argentina), aflatoxins/zearalenone (Brazil, Indonesia), aflatoxins/ Ochratoxin A and aflatoxins/cyclopiazonic acid (Figure 2.6c)/zearalenone (Indonesia), afla-toxins/fumonisins (USA). Given the worldwide distribution of the Fusarium moulds, the presence of combinations of Fusarium mycotoxins and aflatoxins in food and feeds of developing country origin should be expected.
The co-occurrence of mycotoxins can affect both the level of mycotoxin production and the toxicology of the contaminated grain. The presence of trichothecenes may increase the production of aflatoxin in stored grain, for example, whereas some naturally occurring combinations of Fusarium toxins are synergistic in laboratory animals. To date, little is known about this particularly important area of mycotoxicology. The significance of mycotoxins in human disease will become more clearly defined through the continued identification of biomarkers, present in blood and/or urine, which reflect the levels of recent dietary exposure to mycotoxins. Aflatoxin, covalently bound to albumin in peripheral blood, and the urinary aflatoxin B1-guanine adduct have both been used, for example, to monitor aflatoxin ingestion.
Studies using the aflatoxin-albumin adduct have demonstrated the significantly higher exposure that occurs in Gambia, Kenya and the Guangxi region of China, compared with Thailand and Europe. In Europe, the levels of biomarker were below the detection limit.
