Significance and occurrence of fumonisins from Aspergillus niger

Fumonisins is a well-studied group of mycotoxins, mainly produced in maize by Fusarium species. However with the recent discovery of a fumonisin production by Aspergillus niger, other food commodities are at risk, since A. niger is a ubiquitous contaminant of many food and feed products. The objective of this thesis was to determine the significance and occurrence of fumonisins from Aspergillus niger in food, the frequency of fumonisin production in A. niger isolates, as well as studies of the effect of physiological factors affecting fumonisin production.

Major findings in this context have been the ocumentation of the production of fumonisins in raisins and peanuts, and occurrence of A. niger derived fumonisins in retail wine and raisins. Physiological investigations have demonstrated that fumonisin production in A. niger occurs at temperatures between 20-37 °C.

Three water activity lowering solutes, glycerol, NaCl, and sucrose were used. All A. niger strains responded differently on the three solutes. Addition of NaCl and sucrose increased the fumonisin production, where addition of glycerol decreased the production. Fumonisin production in grape and derived products was investigated.

Sixty-six A. niger strains were isolated and screened for a fumonisin production, and 77 % produced fumonisin on agar media. Worst-case scenarios were made by inoculation of A. niger on grapes and solidified the thought that a potential fumonisin production/contamination in grapes and derived products could occur.

All tested A. niger strains produced fumonisins, not only when growing on grapes, but also on dried grapes and re-moistened raisins. By screening of 77 wine and 21 raisins samples, 18 wine (1-25 μg FB2/l) and 10 raisin (1.3-13 μg FB2/kg) samples contained detectable amounts of fumonisins. An investigation of peanuts and peanut butter did not show any sign of fumonisin contamination, even though A. niger produced high amounts of fumonisins in worst case scenarios on shelled peanuts.

Black and puerh tea were also examined, since A. niger were claimed to be the primary black Aspergilli in these. After isolation of 47 black Aspergilli, who all turned out to be A. acidus and did not produce neither ochratoxin or fumonisins, no significant risk from these toxins were associated with this intake.

Single kernel analysis of maize showed that fumonisins were present in 15% of the kernels at varying concentration. The frequency of highly contaminated kernels was 4 %. An estimated calculation showed that the fumonisin content could be reduced with more than 70 % by sorting the maize. Other frequently found fungal metabolites in the maize kernels were chanoclavine, emodin, equisetin, and fusaric acid.

The biotechnologically important fungus Tolypocladium, a producer of the immunosuppressive drug cyclosporin, was identified as a new fumonisin producer. Three species within the genera produced fumonisin B2 and B4, and due to the widespread ability within the genus, it should be determined if this mycotoxin production occurs under industrial settings.