ABSTRACT:
 
A monitoring of potential toxic substances entering into the human food chain is an integral part of each modern human society. The safety control of food and feed is absolutely essential part of prevention of health. Various industrial contaminants, heavy metals, pesticides but also some natural toxins including mycotoxins belong to the monitored substances, especially in the matter of hygienic-toxicological food safety.

The development of human society has been guided by various using of microorganism and also other species from large group of heterotrophic organism since the antiquity. A leaven and microscopic filamentous fungi have been used since the Middle Ages (e.g. for preparing of bread, alcohol drinks, cheeses and various fermented oriental dishes. Modern bio-technologies are using leaven and fungi for preparation of feed, enzymes, organic acids, ethanol, vitamins, antibiotics, steroids, plants grow stimulants etc.

Mycotoxins – secondary metabolism products of microscopic filamentous fungi – primarily appear on farm crops, especially cereals (wheat, barley, rye and oats), rice, maize, oil seeds (poppy, rape, mustard, soybeans and sun-flower) and eventually on food products containing these food sources. Then not least on livestock (e.g. poultry, pigs and cattle), because cereals are one of the basic components of feed. Many studies confirmed an influence of feed contaminated by mycotoxins on health condition and production. The UN Food and Agriculture Organization mention that in 1989 there was more then 25% of world production of food contaminated by mycotoxins. For these reasons the research is more focused in the necessity of the research of these toxins (its appearance, determination of nature of its toxicity, range of residual amount of toxic substances in food and determination of its toxic potential). The main objective is an elimination of risks caused by consummation of such a food and feed by human beings and animals. It is necessary to point out that this topic of mycotoxins is already urgent to solve in the stage of farm products.

People came across the problems caused by consummation of mouldy food from time immemorial, especially when left the nomadic style of life and began to plant farm crops and stored its leftovers. The oldest describeded mycotoxicoses are egotisms, alimentary toxic aleukia and disorder caused by yellow rice. In 60’s of last century a systematic mycotoxins research was initiated due to increasing signals of danger coming from the nutrition by using mouldy food and feed. In 1960 a fundamental motion happened in Great Britain, where there were series of mass decease of about thousand turkeys and other poultry. The investigation came across the evidence of some connection with mouldy feed (peanuts meal), whereas as a reason was determined a "alfatoxin" unknown till then and named according to Latin term of causal organism – a microscopic filamentous fungi Aspergillus flavus.

The optimum leading to the elimination of mycotoxins appearance in human diet and feed contains three basic measures:

• Limitation of the toxicogenic infection caused by filamentous fungi during the vegetation period of farm crops
• Rapid and accurate desiccation of harvested farm crops and its accurate storage
• Using of effective fungicide preparations on both of above-mentioned basic agricultural industry levels

One of the main factors which affect a range of potential contamination of farm crops by mycotoxins in field condition are: self-resistance of cultivar against microscopic filamentous fungal attack, rate of physiological stress inflicted on plants (shortage of minerals, low or high moisture, soil salinity, pollution of air, insects attacks, etc.), pathogen fungi virulence, type of produced mycotoxin, plant ability to degrade mycotoxins, good agricultural practices (tillage type, fertilization, preceding crop) and the time from harvest to mycotoxins production.

This project elaborates on the state-of-the-art of the topic of mycotoxins and its grading, as well the experimental data (a monitoring of natural appearance of Fusarium mycotoxins on cereals in various agricultural areas in the Czech Republic, a monitoring of appearance of Alternarium and Fusarium mycotoxins samples taken from spring-time variety of Hordeum vulgare simultaneously with examination of influence of agricultural practices on its level, etc.).

It can be estimated for practice that the severity of contamination of samples is affected by the resistance of variety against fungi infection and presence of genus or chemotype of microscopic filamentous fungi. Especially the climatic conditions represent an important determinant of current level of contamination in monitored regions during vegetation period for individual years. One of the factors which affect the appearance of fungi infection and production of mycotoxins is not least agricultural technologies (suitable preference of preceding crop, agrochemicals, soil processing, etc.). For instance the maize can be marked as a less unsuitable preceding crop for cereals culture in discussed topic because many organic fragments remain on field after harvest and these fragments represent susceptible substrate for transfer of fungi mycelium.

It is also evident among others from obtained results that DON is not always dominant mycotoxin in the samples contaminated by Fusarium mycotoxins. Thus there is a question of useful using of trichothecenic mycotoxin as marker for keeping of hygienic limits or health safety of food sources. In this context there is very serious fact: the actual toxicity of NIV is more than twice higher compare to DON (according to LD50 for mouse) and a sample of DON corresponding to the hygienic limit can be de under specific circumstances de facto evaluated as a dangerous from the hygiene-toxicological point of view.

As the climatic condition are one of the main factors which affect the appearance of mycotoxins in farm crops, it is lastly necessary to point out that many experiments presented in this report represent the summary of one-year trials only. It will be necessary for general conclusions to carry out more-years field trials in order to consider better the influence of climatic condition on the production of selected mycotoxins.

Furthermore it is necessary to underline a demand on an overall estimation of the application of pesticide and mainly fungicide preparative relate not only to the protection of plants but also in relation to the level of mycotoxins in harvested crops. The carried out experiments have clearly shown the differences between various type of preparations and there has also been occurred causes which has shown increasing amount of secondary pollutants compare to the control tests. The causes like that were no exceptions. The reason of this anomalous effect is the fact that the microscopic filamentous fungi can produce higher levels of toxic co-metabolites on condition of chemical "stress".