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Where are mycotoxins found?

Author: Radka Borutova, DVM, PhD, Alltech mycotoxin management team

Mycotoxins discovery

The term mycotoxin was first used in the 1960s to describe the toxin associated with contaminated peanuts in animal feed and the loss of turkeys in England (Turkey-X-disease). This mycotoxin was later identified as the Aspergillus flavus toxin aflatoxin B1. Bennett (1987) defined mycotoxins as “natural products produced by fungi that evoke a toxic response when introduced in low concentrations to higher vertebrates and other animals by a natural route.”

What are mycotoxins?

Mycotoxins are toxic compounds that are naturally produced by certain types of molds (fungi). Molds that can produce mycotoxins grow on numerous foodstuffs such as cereals, dried fruits, nuts and spices and feedstuffs such as corn, wheat, barley, silage, haylage, grass, etc. Mold growth can occur both before and after harvest, during storage, on/in the feed or food itself, often under warm, damp and humid conditions. Most mycotoxins are chemically stable and survive food and feed processing.

Several hundred different mycotoxins have been identified, but the most commonly observed mycotoxins presenting concern to human health and livestock include aflatoxins, ochratoxin A, patulin, fumonisins, zearalenone and nivalenol/deoxynivalenol. Mycotoxins appear in the food chain because of mold infection of crops, both before and after harvest. Exposure to mycotoxins can happen either directly — by eating infected food or feed — or indirectly from animals fed contaminated feed, particularly from milk.

Mycotoxins and fungi

Traditionally, toxigenic fungi contaminating agricultural grains have been conventionally divided into two groups: those that invade seed crops, described as “field” fungi (e.g., Cladosporium, Fusarium, Alternaria spp.), which reputedly gain access to seeds during plant development, and “storage” fungi, (e.g., Aspergillus, Penicillium spp.), which proliferate during storage (Legan, 2000).

Currently, this division is not so strict because, according to Miller (1995), four types of toxigenic fungi can be distinguished:

(1) Plant pathogens (e.g., Fusarium graminearum and Alternaria alternata).

(2) Fungi that grow and produce mycotoxins on senescent or stressed plants (e.g., F. moniliforme and Aspergillus flavus).

(3) Fungi that initially colonize the plant and increase the feedstock’s susceptibility to contamination after harvesting (e.g., A. flavus)

(4) Fungi found on the soil or decaying plant material that occur on the developing kernels in the field and later proliferate in storage if conditions allow (e.g., P. verrucosum and A. ochraceus).

Among the hundreds of known mycotoxins, aflatoxins, citrinin, patulin, penicillic acid, tenuazonic acid, ochratoxin A, cytochalasins, deoxynivalenol, fumonisins, fusarin C, fusaric acid and zearalenone are considered the types that most contaminate cereal grain. The majority of the mycotoxins in these groups are produced by three fungal genera: Aspergillus, Penicillium and Fusarium. These metabolites primarily affect seed quality, germination, viability, seedling vigor, root growth and coleoptile. Additionally, since the fungi responsible for producing these mycotoxins are often endophytes that infect and colonize living plant tissues, accumulation of mycotoxins in the plant tissues may, at times, be associated with the development of plant disease symptoms (Ismaiel and Papenbrock, 2015). The presence of mycotoxins, even in the absence of disease symptoms, may still have subtle biological effects on the physiology of plants and, therefore, after ingesting, also the physiology of the animals.

 * References available on request.