Citrinin is a naturally occurring mycotoxin, a toxic secondary metabolite produced by specific types of filamentous fungi. This polyketide compound was first isolated in the 1930s from the mold Penicillium citrinum. Initial research focused on its potential as a broad-spectrum antibacterial agent, but interest declined after studies revealed its toxicity to mammalian systems. Citrinin is frequently studied alongside Ochratoxin A, as they often contaminate the same food sources.
Fungal Origin and Common Food Sources
The production of citrinin is primarily associated with several fungal species belonging to the genera Penicillium, Aspergillus, and Monascus. Penicillium citrinum is one of the most common producers found in various food and feed products globally. Contamination typically occurs after harvest when agricultural commodities are stored under inappropriate conditions. High moisture and elevated temperatures promote the proliferation of these fungi and the subsequent production of the mycotoxin.
Citrinin contamination affects a wide variety of foodstuffs. Stored grains and cereals are among the most commonly affected commodities. The toxin has also been detected in:
- Widely consumed staples such as rice, wheat, barley, oats, and maize.
- Spices, roasted nuts, and dried beans.
- Fruits and dairy products like cheese.
One significant source of consumer exposure is red yeast rice (RYR), made by fermenting rice with the fungus Monascus purpureus. RYR is traditionally used in Asian cuisine and is widely available globally as a dietary supplement. If the fermentation process is not strictly controlled, the Monascus species can inadvertently produce citrinin. Consumers relying on these supplements should be mindful of the potential for unintended mycotoxin exposure.
How Citrinin Affects the Body
Upon ingestion, citrinin primarily targets the kidneys, a toxic effect known as nephrotoxicity. Renal tissue is significantly more susceptible to damage from citrinin than other organs, such as the liver. The toxin interferes directly with the energy-producing structures within renal cells, known as mitochondria.
Citrinin disrupts the mitochondrial respiratory chain, the process that generates the cell’s main energy currency, Adenosine Triphosphate (ATP). This interference involves inhibiting key components, particularly Complex I and ATP synthase. The resulting decline in ATP compromises the cell’s ability to function, leading to cellular dysfunction and eventual cell death. Furthermore, citrinin induces severe oxidative stress within renal cells through the excessive production of Reactive Oxygen Species (ROS).
While its effect on the kidneys is the most well-defined risk, citrinin also exhibits other toxic properties. Research indicates that it is genotoxic, meaning it can damage genetic material. Studies in animal models have shown that citrinin can be embryotoxic and teratogenic, suggesting potential harm to developing fetuses. The toxin has also been implicated in mycotoxic nephropathy in livestock and is suspected to contribute, along with Ochratoxin A, to Balkan Endemic Nephropathy in humans.
Safety Standards and Preventing Exposure
Regulatory bodies globally have taken steps to monitor and limit human exposure to citrinin through food. The European Food Safety Authority (EFSA) established a level of no concern for nephrotoxicity at 0.2 micrograms per kilogram of body weight per day. This threshold guides regulatory decisions regarding acceptable contamination levels in various food products.
While a broad maximum limit for citrinin across all foodstuffs has not been set in the European Union, a specific regulation exists for high-risk products. Food supplements derived from red yeast rice are subject to a strict maximum limit of 100 micrograms of citrinin per kilogram of product (\(\mu\)g/kg). This regulation aims to protect consumers who ingest these supplements regularly.
To ensure compliance, food safety agencies utilize highly sensitive analytical techniques. Methods such as High-Performance Liquid Chromatography (HPLC) coupled with Mass Spectrometry (MS) allow for the precise detection and quantification of the mycotoxin in food samples. For consumers, prevention centers on reducing opportunities for mold growth. All stored food, especially grains and cereals, should be kept in cool, dry conditions with low moisture. Any food showing visible signs of mold should be discarded immediately.