Citrinin

Citrinin is a nephrotoxic mycotoxin, and on cured meat it is the near neighbour of ochratoxin A: the second toxin made by Penicillium verrucosum, favoured when ochratoxin A is not. Its name comes from the mould it was first found in, Penicillium citrinum, whose epithet means lemon-yellow, and the toxin is itself a yellow pigment, which is why it turns up in the red-pigment fermentations of Monascus as well.

It is one of the oldest known mycotoxins, isolated in 1931 by Hetherington and Raistrick from a culture of Penicillium citrinum. Chemically it is a small pentaketide, structurally related to ochratoxin A, and it is produced by a scatter of moulds across three genera: several Penicillium species, including Penicillium citrinum, Penicillium verrucosum and Penicillium expansum; some Aspergillus species; and Monascus purpureus, the red yeast used to ferment red yeast rice. Its main reservoir is stored cereals, where it often occurs alongside ochratoxin A, and its most contaminated food form is red yeast rice sold as a supplement, where levels can run high.

Like ochratoxin A, its principal target is the kidney. It damages the distal tubules and impairs renal function, and it is also hepatotoxic, genotoxic, teratogenic and immunotoxic. The two toxins are thought to act in synergy in the kidney, each worsening the other, and citrinin has been implicated alongside ochratoxin A in the endemic nephropathies seen in pigs and, less certainly, in people. Because the research base is thinner than for ochratoxin A, the International Agency for Research on Cancer places it in group 3, not classifiable as to its carcinogenicity to humans, which reflects a lack of data rather than a clean bill.

**How it endangers cured meat.** On a ripening rind or casing, citrinin comes chiefly from Penicillium verrucosum, the same mould that makes ochratoxin A, and the choice between the two toxins turns on salt: at low salt the mould tends to make citrinin, and as salt rises its output shifts towards ochratoxin A, so the salted surface of a dry cure pushes P. verrucosum towards the ochratoxin and citrinin is the greater risk where salt is low or uneven. It is not, however, the only source. Unselected strains of the surface Penicillia can produce citrinin too, including wild relatives of the very species used as noble white moulds, Penicillium nalgiovense and Penicillium chrysogenum; the commercial cultures of those are chosen and toxin-screened to be safe, but the chance flora of an uncontrolled surface is not, which is one more reason to inoculate a known strain rather than trust what settles.

The way the toxin behaves on the meat also differs from ochratoxin A in a way worth knowing. Toxigenic moulds can produce citrinin on dry-cured meat in quite high amounts, but it is far less persistent there than ochratoxin A: on ham its half-life runs to only a few hours, against several days for ochratoxin A, so the citrinin decays while the ochratoxin lingers. That is part of why ochratoxin A dominates the lasting risk on cured meat, though citrinin still matters wherever toxigenic moulds are allowed to grow. Citrinin is also less heat-stable than ochratoxin A, degrading during cooking and thermal processing and reacting with the sugars and proteins of the food into modified forms; but a raw, uncooked dry cure gains little from that, so on cured meat it remains a toxin to prevent rather than to cook or dry away.

Citrinin is regulated narrowly. Following an EFSA opinion in 2012, the European Union sets a maximum level only for food supplements based on rice fermented with red yeast Monascus purpureus, reduced from 2000 to 100 micrograms per kilogram in 2020 and now carried in Regulation (EU) 2023/915; there is no maximum level for meat, cured meat or other foods, the view being that red yeast rice supplements are the exposure that matters. In its 2012 assessment EFSA could not set a health-based guidance value from the available data, but derived a level of no concern for nephrotoxicity of 0.2 micrograms per kilogram of body weight per day, while noting that a concern for genotoxicity and carcinogenicity could not be excluded even at that level.

Control on the meat is the surface strategy of Mould Control, the same as for the other ochratoxigenic moulds: a noble white mould inoculated to hold the rind, a protective house flora, and managed water activity, temperature, humidity and air movement through ripening. The one twist particular to citrinin is that a low or uneven salt level, which a maker might not think of as a mould risk, is precisely what favours it.