Ingresos económicos de los Minero Artesanales

Mycotoxins are natural compounds. They are produced by fungi and some constitute a well known hazard to humans and domestic animals. Relatively simple precautions

concerning harvest, drying and storage can help preventing the proliferation of toxigenic fungi. It is important to avoid soil contamination and reduce the amount of weed debris and immature kernels as much as possible in the harvested crop. Harvest and drying facilities should be cleaned properly. Furthermore, it is crucial to dry the grain quickly – especially if it has been harvested with moisture contents above 17% – as grain moisture is very important for mycotoxin production. Drum drying has proven very efficient for simultaneous fast grain drying and elimination of fungal propagules on the kernel surface without reducing the baking quality.

Mycotoxins are naturally occurring toxins. They are formed by fungi and some of them constitute a serious health threat to humans and domestic animals. Ochratoxin A (OTA) and trichothecenes are the most important mycotoxins in Danish grain. Danish surveillance reports of small grain cereals from 1986- 000 showed that especially organically grown rye was sensitive to OTA. It is important to know how seed treat- ment, harvest, drying and storage practice in organic farming affect the risk of mycotoxin formation. The project had the following objectives:

■ Studying the effect of different drying systems, especially

drum drying

■ Increasing our knowledge on the ecology of toxigenic

fungi

■ Pointing to farming practices that will reduce the

abundance of toxigenic fungi

Comparison of different drying techniques

A new drum drying technique has been implemented for use in rye. The effect has been compared with other drying techniques regarding fungal occurrence in the grain and baking quality:

1. Drum drying (retention time 10.5 min.; grain temperature 6ºC)

. Continuous drying (drying air max. 65ºC; grain temperature max. 45ºC)

3. In-bin drying (optimal heat treatment)

4. In-bin drying (no heat treatment, insufficient aeration) The experiments showed that drum drying was extremely efficient in reducing the number of fungal propagules on the grain – including the OTA forming species (Penicillium verrucosum). The effect of drum drying was much better than continuous drying and in-bin drying.

Seed quality and harvest practice

The project has elucidated the importance of seed quality and harvest practice on the occurrence of Penicillium verru- cosum and its toxin – ochratoxin A (OTA). We conducted a field trial with grain that was naturally contaminated by P. verrucosum. The aim was to find out if contaminated seed can lead to growth and OTA production of the fungus in soil. We also investigated if contaminated seed increases the risk

of contamination of the standing crop prior to harvest. The results did not confirm either.

Within the context of this subproject, a M.Sc. project addressed the problems with P. verrucosum in on-floor drying. The conclusions were that the fungus with great probability had been disseminated to the grain via insufficiently cleaned drying ducts. The results showed a significant increase in number of kernels contaminated by P. verrucosum during the period of drying and storage. Contamination was more heavy in rye than in oats and more so in the bottom layer of the batch close to the side ducts than in the upper layer. In lab trials, we investigated how grain damage, grain moisture and temperature affected OTA formation and growth of P. verrucosum. Rye was inoculated with conidia of

P. verrucosum. A part of the grain was mechanically damaged to simulate threshing damage. The purpose was to elucidate

I.12 Pr e ven ting My co toxin Pr oblems (PRE MY TO X) Drum drying

if damaged grain is more sensitive to fungal growth and OTA formation than undamaged grain. The experiments showed that grain moisture is more important for OTA- formation than temperature and apparently also more important than whether the grain is damaged or not. Within the context of this subproject, we have cooperated with Bio-Centrum at the Technical University of Den- mark on studies on genetic variability in P. verrucosum from different regions of Europe. The PREMYTOX project contributed with 87 isolates from two different farms. The results showed a surprisingly high variability in isolates from the same farm and this is important for further studies on the distribution of the species on a large scale (countries, regions) and on a small scale (seed, field, grain store).

Growth of P. verrucosum on rye

Practical precautions to prevent problems with ochratoxin

Based on the results of the project, the following advice can be given:

■ The OTA forming P. verrucosum is present in some

soils and apparently more frequent in organically than conventionally cultivated soils. Therefore, soil contami- nation during harvest should be avoided.

■ Field trials did not indicate P. verrucosum to be seed borne.

The fungus is, however, often present in threshed grain. Harvest machinery should be cleaned properly and the combine harvester adjusted to minimize kernel damage.

I.12 Pr e ven ting My co toxin Pr oblems (PRE MY TO X) Project leader

Susanne Elmholt, senior scientist Danish Institute of Agricultural Sciences, DK- 8830 Tjele

E-mail: [email protected]

Project participants

Erik Fløjgård Kristensen, Danish Institute of Agricul- tural Sciences and Ulf Thrane, Technical University of Denmark

Publications and further information

See the project website:

www.darcof.dk/research/darcofii/i1.html and the internet-archive: www.orgprints.org

■ Quick drying is crucial, especially when the grain is

harvested with moisture contents above 17%. Earlier studies indicated that problems with P. verrucosum were not necessarily linked to the organic farming system but rather to inappropriate drying conditions. Experiments with drum drying have shown that this technique is very efficient in reducing the number of fungal conidia on the grain – even without destroying the baking quality.

■ The grain should be winnowed if it contains large

amounts of impurities. This may result in ”damp pockets” because the impurities often contain more moisture than the grain itself. If such pockets contain P. verrucosum, this may lead to OTA formation even at low temperatures.

■ Driers, that are difficult to clean, may contaminate the

grain heavily with conidia of P. verrucosum – especially if drying is slow. Large amounts of conidia will not always result in high contents of OTA, but it involves a risk if the environmental conditions become conducive to the germination, growth and toxin formation. It is therefore important that the drier is properly cleaned. Take care that the conidia are actually removed – not just whirled up. A powerful vacuum cleaner is advisable.

Greenhouse gas emission and