Contamination and damage of grain and feeds by micromycetes

Abstract

Toxin-producing micromycetes are widespread in nature and are damaging food and animal feeds, causing serious problems in humans as well as farm animals by its toxic effects. The contamination of foods and animal feeds with mycotoxins is a worldwide problem. Studies of species composition of the toxigenic fungi suggest being international. This problem is particularly relevant at present market conditions and growing agricultural exports. Such products must be mandatory certificated and have required quality and safety.

Regardless of decades of extensive research, mold infection still remains a challenging problem. According to the Food and Agriculture Organization of the United Nations (FAO), at least 25 percent of the world's food crops are contaminated with fungal toxins. Therefore, it is important to control of mycotoxin contamination of food and feed raw components.

Mycotoxin-contaminated feed has adverse effects on animal health and productivity. Field fungi can cause considerable damage to grains. The nutritional value of such grain and feed is reduced because low calorie, negative impact on health of human, farm animals and poultry.

Economic losses from micromycetes and their toxins are determined not only by decreasing of quality, but also the animal death, increasing susceptibility to infectious diseases, mycotoxin contamination of conventional animal products.

Mold contamination of feed contributes to some environmental factors (soil and climatic conditions, application of fertilizers and plant protection chemicals, etc.) that define natural diversity of micromycetes. The feed is a source of the amino acids and trace elements that is also favorable nutrient substrate for development of disease activators such as mycoses and mycotoxicoses of livestock.

Mycological and toxicological studies on feed have found correlative relationship between appearance of animal mycotoxicoses and damage level of feed substrate with toxigenic species of fungi. Therefore, information on species composition of micromycetes in feed is an integral part of their quality and safety determination.

The aim of research was to study the species composition of toxigenic micromycetes contaminating and damaging of corn, oat, winter wheat and soybean grain. Mycological and statistical methods were used for research.

Twenty-four fungal species of micromycetes were isolated and identified as a result of mycological analysis of grain samples. The most abundant fungal species were isolated from corn and oat, accordingly 14 and 15 species. The lowest diversity of mycobiota was found in winter wheat grain (10 species).

Plant pathogens were identified among of isolated fungi that defeat vegetative plants and can continue their development during the storage as saprotrophs. It was fusariosis (activators Fusarium spp.), white rot (Sclerotinia sclerotiorum), grain discoloration (Nigrospora oryzae) and leaf spot (Drechslera sp.).

Fusarium species are the most important grain contaminants with mycotoxins during vegetation period and storage. These fungi are well known producers of vomitoxin (DON), T-2 toxin, HT-2 toxin, zearalenone, fumonisin. Not all mycotoxins are detected in routine testing by laboratories. Therefore, standard detection of one or two mycotoxins in feed (DON and zearalenone) can lead to underestimation of the total content, the risk of mycotoxicoses also increases.

In the vast majority of fungal species isolated from grain samples were saprotrophs that belonged to storage mold. It was fungi-activators of different types of mold: green – Asprgillus sp., Penicillium sp., Myrothecium verrucaria, grey – Mucor sp., Rhizopus sp., pink – Trichothecium sp., black mold – Alternaria sp., Cladosporium sp., Epiccocum sp. Among of them toxic properties are known to the genera Aspergillus P. Micheli ex Haller (aflatoxin, ochratoxin A producents), Penicillium Link (patulin, ochratoxin A), Myrothecium Tode (verrukaryn A, H; rorydyn A, H, E, trichothecene) and Trichothecium Link (trichothecene).

Micromycetes Arthrobotrys sp., Chaetomium globosum, Cephalotrichum stemonitis, Geotrichum candidum, Harzia acremonioides, Papularia sp. are cellulolytic species that develop mainly in soil and on dead plant debris and are not known as producents of toxic compounds to human and farm animals.

Different levels of damage by toxigenic micromycetes were found in investigated grain of crops. Soybean, oat, corn and winter wheat were the greatest to Fusarium spp. growth 15,8%, 8,2, 5,0 and 2,3% accordingly; oat, soybean and corn – to Aspergillus spp. 4,2%, 1,7 and 0,8% accordingly; corn and oat – to Penicillium 29,2 and 4,1%; oat – to Trichothecium roseum (17,5%). Along with representatives of the genus Fusarium, microscopic fungus Aspergillus flavus was isolated from grain of soybean and corn, it strains detected on these cultures often described as toxic.

In conclusion, identified micromycetes composition and level of damage of soybean, oats and corn, may indicate its probable contamination with mycotoxins. This is consistent with findings of other researchers.

Forage, including wheat, oats, corn and soybean are particularly susceptible to mycotoxin contamination. A large proportion of these grains go into the animal feed as it part. The accumulation of mycotoxins in combined feed is always greater than the levels found in the grain. The accumulation of mycotoxins in animal feed is due to synergistic interactions of the fungal toxic metabolites of feed ingredients. Such components of animal feed as wheat bran, processed soybeans and corn, may also be contaminated with mycotoxins.

Thus, mycological and toxicological analysis should be performed for accurate risk assessment of appearance of mycotoxicoses and pollution of samples of animal feed and feed ingredients, particularly corn, by mycotoxins.

Keywords: grain, feed, toxigenic micromycetes, mycotoxins