What is patulin?
Patulin is a toxic fungal metabolite (mycotoxin) produced by certain moulds of the genera Penicillium, Aspergillus and Byssochlamys growing on various food commodities, especially fruit. Patulin exhibits a number of toxic effects in animals and its presence in food is undesirable.
Chemically, patulin is a polyketide lactone. It is a relatively small molecule (C7H6O4) and is soluble in water.
What foods can be contaminated
Patulin occurs most often in apples that have been spoiled by mould growth, or in products made from spoiled apples, such as apple juice, pies and conserves. It has also been found in other fruits, including pears and grapes, in vegetables and in cereal grains and cheese.
Apples and apple products are considered to be by far the most significant contributor to patulin in the diet. Contaminated apple juice usually contains patulin at levels below 50 μg/litre, but much higher levels (up to 4,000 μg/litre) have been reported occasionally.
How does it affect human health?
Most of the information on the toxicity of patulin is derived from animal studies and there is little or no experimental, or epidemiological, data on acute or chronic toxicity in humans.
At relatively high doses, patulin is acutely toxic in mice and rats, causing gastrointestinal lesions, distension and haemorrhage in the stomach and small intestine. However, it is possible that these effects are due to the selective antibiotic action of patulin against Gram-positive bacteria, which may give Gram-negative intestinal pathogens an advantage. LD50 values (lethal dose) of 20-100 mg/kg bodyweight have been reported for patulin administered orally to mice and rats. These levels are much higher than those likely to be encountered in human diets. Relatively high doses of patulin have also been shown to be immunotoxic and neurotoxic in animals.
Of more concern from a food safety point of view are longer term chronic effects. It has been suggested that patulin could be a carcinogen at low levels in the diet, but the International Agency for Research on Cancer (IARC) has reviewed the available data and concluded that there is no convincing evidence of carcinogenicity in animals or in humans, other than at extremely high doses.
Data from feeding experiments have been used to derive a no observed effect level (NOEL) of 43 μg/kg bodyweight per day and a provisional maximum tolerable daily intake (PMTDI) for humans of 0.4 μg/kg bodyweight. This is well above the maximum daily intake levels estimated for adults and children (0.1 and 0.2 μg/kg bodyweight respectively).
How common is illness?
Although patulin is considered potentially toxic there is very little data to indicate the incidence of any adverse health effects in humans and no unequivocal documented outbreaks of illness.
Where does it come from?
Patulin is produced by certain species of Penicillium, Aspergillus and Byssochlamys, notably Penicillium expansum and Aspergillus clavatus. P. expansum is the most significant producer of patulin, as it is a common cause of rots in apples. Patulin production by P. expansum has been reported over a temperature range from 0-25oC and over a pH range in apple juice of 3.2-3.8.
Is it stable in food?
Patulin is relatively heat stable and is not destroyed by pasteurisation of apple juice at 90oC for 10 seconds. However, it is broken down in fruit juice and other foods in the presence of sulphur dioxide used as a preservative. It does not appear to survive fermentation processes and is not usually found in alcoholic drinks, such as cider, but the toxicity of its breakdown products is uncertain.
Patulin produced by mould growth on cheese is inactivated by interaction with high cysteine levels.
How can it be controlled?
Patulin is only considered to be a significant problem in apples and apple products, especially apple juice.
For primary producers
Good Agricultural Practice (GAP) measures designed to minimise insect and bird damage to apples can help to prevent mould infection and patulin production before harvest.
At harvest, rotten and damaged apples should be discarded, as these are much more likely to contain patulin.
Control in harvested apples is best achieved by good storage practice designed to ensure hygienic conditions in apple stores and to minimise physical damage that might promote fungal infection and rotting. Storage at temperatures of less than 10oC is also a useful control measure.
For food processors
Physical separation of mouldy and damaged apples before processing will help to reduce patulin levels in apple juice and other apple products. This can be done by hand, or by using water flumes or high-pressure water jets. Washing of apples can also help to reduce patulin levels.
For enforcement agencies
Monitoring of patulin levels in susceptible products, such as apple juice, by sampling and analysis can be valuable – the test method of choice being HPLC with UV detection. In the UK, significant reductions in patulin levels in apple juice have been achieved since regular monitoring was implemented in 1992.
Are there rules and regulations?
Although patulin is now considered to be a less significant food safety hazard than previously, a number of countries have introduced regulations specifying maximum permitted levels in susceptible products.
The EU has set a maximum limit for patulin of 50 μg/kg in fruit juices and in drinks containing apple juice or derived from apples. For solid apple products, such as apple puree, the limit is 25 μg/kg. A lower limit of 10 μg/kg has been set for certain foods intended for infants.
The FDA has set an upper limit of 50 μg/kg for patulin in apple juice and apple juice concentrates.
The Codex Alimentarius Commission has also set a recommended upper limit of 50 μg/kg for patulin in apple juice and apple ingredients in other beverages.