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Department of Safety and Quality of Fruit and Vegetables

Prevention strategies for mycotoxins

Mycotoxins are toxic metabolites of filamentous fungi and are a problem with respect to the safety of various foods and feeds. According to estimations of the FAO, up to 25 % of the yearly harvest of plant products are contaminated by mycotoxins and must be discarded. Up to now, no comprehensive concepts exist to prevent mycotoxin contaminations in foods and feeds. Filamentous fungi occur ubiquitously. Because of this fact, only exact knowledge about the growth conditions for fungi, and the regulation of mycotoxin biosynthesis, allow the development of new prevention strategies. Important mycotoxin producing fungi are the Fusaria (fumonisins, trichothecenes, zearalenon), the Aspergilli (ochratoxin, aflatoxin, sterigmatocystin) and the Penicillia (ochratoxin, citrinin, patulin). Because of the capacity of fungi to grow on different food environments, mycotoxins can be found on cereals, coffee, cacao (ochratoxin, trichothecenes), maize (fumonisins, aflatoxin), grapes, wine (ochratoxin), spices and nuts (aflatoxin, ochratoxin), and apple products (patulin). Because of the importance of mycotoxins for the health of man and animals, regulatory limits have been set in the EU for all important mycotoxins. Foods and feeds are regularly analysed by governmental inspection agencies. Only products which are below the limits can be sold to the consumer.
Often growth and mycotoxin biosynthesis are not directly coupled.  This has led to the situation that visibly molded products may not contain mycotoxins. Mycotoxin biosynthesis is dependent on the external conditions like temperature, humidity or the pH of a food product, but also on internal conditions like growth phase or nutritional status of the fungal cell. On the other hand, also without visible fungal growth, mycotoxins may be present in a sample. This regulation is controlled at the genetic level. While analytical methods are some kind of end-point control, molecular methods can monitor gene activation before measurable amounts of toxins are produced. This may enable the application of measures to prevent the production of mycotoxins. Scientists of the Department of Safety and Quality of Fruit and Vegetables at the Max Rubner-Institut in Karlsruhe analysed the regulation of mycotoxin biosynthesis of various fungal species on their respective habitat. Within these approaches, it could be realized that light of a certain wave length has a strong influence on growth and mycotoxin biosynthesis of fungi. Fungi like the Fusaria, the Aspergilli or the Penicillia, carry different light receptors, which can perceive light of different wave lengths. These light receptors can activate different signal cascades themselves, which may include signal cascades responsible for mycotoxin biosynthesis.
White, red, but especially blue light inhibits growth and mycotoxin biosynthesis of Penicillia, whereas yellow and green light rather acts supportive. The Fusaria and the Aspergilli produce pigments, like carotenoids and melanin, which protect against light. For this reason, they are more resistant. The advantage of this approach over the usage of UV light is the fact that the light used is less energy-rich. Due to this, less photo-oxidative changes of treated foods can be expected. Other methods to inhibit the growth of fungi are salting of foods, the addition of preservatives or changes in pH by ascorbic- or citric acid. Also a reduction in the temperature, e. g. in the refrigerator or a reduction of humidity can reduce the germination and growth of fungal spores.