Ochratoxin A

Ochratoxin A is the mycotoxin at the centre of mould safety in dry curing. It is a secondary metabolite made by certain moulds, chemically a chlorinated dihydroisocoumarin joined to the amino acid phenylalanine, and this resemblance to phenylalanine underlies part of its toxicity. It is the most common and most toxic of the ochratoxins, a small family that also includes the less harmful ochratoxin B, which lacks the chlorine, and ochratoxin C. Its name records where it was first found: it was isolated in 1965 from a culture of Aspergillus ochraceus in South Africa, the ochre-coloured mould giving both the toxin and the family their name.

It is produced by two groups of moulds. Among the aspergilli, Aspergillus ochraceus, Aspergillus westerdijkiae and Aspergillus steynii produce it in warmer conditions, along with Aspergillus carbonarius and Aspergillus niger on grapes and coffee. Among the penicillia only two species make it: Penicillium verrucosum, chiefly on cereals in cold and temperate climates, and Penicillium nordicum, the specialist of salted, protein-rich foods and the main producer on dry-cured meat.

Its main target is the kidney. It is nephrotoxic, and in animal studies it is a potent kidney carcinogen; it is also hepatotoxic, immunotoxic, teratogenic and genotoxic, though the evidence suggests the DNA damage comes by way of oxidative stress rather than the toxin binding DNA directly. It is concentrated in the kidney by the transporters that normally handle organic acids, which is part of why the kidney bears the damage, and once absorbed it binds tightly to blood proteins and is cleared only slowly, with a half-life in humans on the order of a month, so repeated small intakes accumulate. Pigs are especially sensitive, and in them it is the recognised cause of mycotoxic porcine nephropathy, with the toxin distributed kidney before liver before muscle before fat. In people it was long suspected as a cause of Balkan endemic nephropathy, a fatal kidney disease with a high rate of urinary-tract tumours, though the European authorities now regard that link as unproven. The International Agency for Research on Cancer classes it as a possible human carcinogen, group 2B. It is chemically stable and survives normal cooking and processing, with meaningful destruction only above about 180 C, or 356 F, so it cannot be removed once it has formed.

**How it endangers cured meat.** In dry curing it forms on the surface, on the rind of ham and the casing of sausage, where ochratoxigenic moulds grow during ripening. The conditions of the craft can work against the maker: the salted, moist surface and the long, cool ripening favour Penicillium nordicum, and salt itself increases the toxin that species produces by inducing the genes for its synthesis. Surveys bear the risk out. The toxin is found in a sizeable fraction of dry-cured products, with one Netherlands survey detecting it in about forty per cent of samples at low levels, and measured contents reaching roughly ten micrograms per kilogram in prosciutto and a few micrograms per kilogram in dry-fermented sausage. The exposure is therefore low but frequent. Because the toxin is stable, no later step removes it, so it must be prevented rather than corrected, and because a toxigenic mould can resemble the noble one and can produce toxin without obvious growth, prevention cannot rely on inspection.

The regulatory picture reflects a hazard still under study. In 2006 the European Food Safety Authority set a tolerable weekly intake of 120 nanograms per kilogram of body weight, based on kidney damage. On reassessing the evidence in 2020 it concluded that this value was no longer protective given the toxin's genotoxic and carcinogenic properties, moved to a margin-of-exposure approach, and found a possible health concern for most consumer groups, without setting a new tolerable intake. The Joint FAO and WHO expert committee has worked to a similar provisional figure of around 100 to 112 nanograms per kilogram per week. Ochratoxin A is regulated in the European Union under Regulation (EU) 2023/915, which sets maximum levels in cereals, dried vine fruit, coffee, wine, spices and other plant foods; there is no maximum level for meat or cured-meat products, the stated position being that further monitoring is needed before one is set, so cured meat is watched rather than limited.

Control on the meat is the surface strategy that Mould Control describes: inoculating a noble white mould to occupy the rind, maintaining a protective house flora such as Debaryomyces hansenii, and managing water activity, temperature, humidity and air movement through ripening.