Aspergillus ochraceus

Aspergillus ochraceus is the type species of the yellow aspergilli, section Circumdati, and gave the group its older working name. The species name is its colour: ochraceus, ochre, for the dull yellow-brown of its spore heads. Like the rest of the genus it carries the fine spore-bearing brush that gives Aspergillus its name.

It has a central place in the history of ochratoxin. When ochratoxin A was first isolated in 1965, it was from a culture named Aspergillus ochraceus, and for the next forty years this species was described as the principal ochratoxin-producing Aspergillus. That account was revised in 2004, when Frisvad and Samson used molecular methods to divide the group and showed that several of the strongest toxin producers, including the original 1965 isolate, were the newly described Aspergillus westerdijkiae and Aspergillus steynii. A. ochraceus remains a genuine ochratoxin producer and can make large amounts under warm conditions, but much of what older meat studies attributed to it is now thought to have been A. westerdijkiae. The two are near-identical in appearance and are reliably separated only by DNA.

**How it endangers cured meat.** In the same way as Aspergillus westerdijkiae: as a warm-favouring surface mould that can produce ochratoxin A on a ripening rind. Ochratoxin A is nephrotoxic and is classed by the International Agency for Research on Cancer as a possible human carcinogen, group 2B. It sits alongside Penicillium nordicum among the surface toxin-formers that Mould Control exists to keep off the meat.

The control is the same as for its relative: a noble white mould inoculated to establish first, a protective house flora, a steady microclimate, a falling water activity, and the removal of wild growth. The fuller account of the mechanism and the control trials is in the westerdijkiae article.