Everything About Aflatoxin
Pistachios, hazelnuts, and almonds are the most popular tree nuts. Pistachio seeds are very substantial owing to their high nutritional value. Pistachios are the lowest in fat and calories, they are among the highest in fiber content for a nut (3 grams per serving). A fist full of pistachios makes a satisfying, healthy snack for just about 100 calories per serving a smart choice when watching your weight. Although they are most of the time not fresh, which leads to the germination of toxic compounds like mycotoxins.
Aflatoxins (AFs) are the most toxic mycotoxins and pistachios can easily be contaminated with them. Contamination of pistachios by aflatoxin may happen at three different stages: when the nuts are still on the tree, when they are dehulled, rinsed and sorted, or in storage, especially when pistachio nuts are stored under unfavorable circumstances of temperature and relative humidity.
What are Aflatoxins?
Aflatoxins are a member of closely related secondary metabolites produced by some strains of moulds. These are one of the most toxic mycotoxins  and are such highly toxic compounds that even low levels of contamination can be dangerous. Different food products, including nuts, cereals, cocoa, dried fruit, spices, pulses, oil seeds, and beans, are contaminated with Aflatoxin. The Pistachio nut is a product with the highest risk for aflatoxin contamination. Since aflatoxin contamination is unpredictable and unavoidable, authorized aflatoxin levels are regulated in many countries worldwide.
“Institute of Standards and Industrial Research of Iran (ISIRI) has set a MTL of 5 and 15 ng/g for AfB1 and total aflatoxins, respectively (ISIRI. 2016). European Commission regulating set limits for AFB1 and total AFs 2 and 4 to 10 ng/g respectively in pistachio. Due to the significant health risks associated with the presence of aflatoxins in foods, it is important to establish a data collection on the occurrence of these toxins in nuts as valuable foods.”
How to prevent Aflatoxin contamination?
A prevention plan should consider different steps from cultivation through harvesting, post harvest handling, drying, post drying storage, processing, post processing storage, transportation and marketing.
- Pistachio trees should be harvested ASAP after maturation to prevent quality loss and reduce problems such as fungal attack and infestation with insects and bugs.
- Signs of harvesting time are: separation of the hull from the shell; drying of kernel and hull, decrease in fruit removal force.
- In hand-picking of younger trees, you should use clean traps to prevent contact of the nuts with litter and soil.
Post harvest handling
- Pistachios should be dried and hulled soon after harvest to reduce shell staining and corrosion to assure safety.
- The nuts should be sorted before cold storage to eliminate imperfect nuts, leaves, twigs and other foreign substances.
- In the two-stage process, the hulled nuts are first dried for about three hours in a column dryer or a rotating drum dryer (air temperature around 82°C) to reach kernel moisture of 12 to 13 percent. Nuts are then transferred to a flat-bottomed grain bin (second stage) where they continue drying with warm air (temperature less than 49°C) for one to two days to reach a moisture content of 5 to 6 percent.
- In the single-stage process, a self-unloading bin dryer is used at an air temperature of 60° to 66°C. Drying time is eight hours .
Further research is required to explore other ways of preventing mold contamination and aflatoxin production. These could involve prevention of contamination in the field by the use of biological control agents that are pathogenic to Aspergillus flavus, such as fungus or harmless bacteria, and that could serve as ecologically friendly bio-competitors . Experts are investigating a genetically engineered antibody to virus production, which could be executed when conditions are favorable to toxin production.
Finally, research is needed to produce pistachio cultivars that are more resistant to aflatoxin.
You can find out more about pistachios on our other blog posts on A Complete Guide to Pistachio Industry and Everything about Pistachios. Read Frequently Asked Questions about Pistachios or contact us for any pistachio questions.
 Molina and Giannuzzi, 2002; Passone et al., 2010; Sardin et al., 2011
 FAO, 1979; Katz, 1996