France
February 14, 2011
Harvested wheat grains can be contaminated by fungi such as Fusarium which can lead to the production of mycotoxins (and particularly deoxynivalenol, or DON), the maximum authorised level of which is fixed by European legislation. It is therefore essential to study how DON is distributed in grain and whether fractionation processes affect the amounts present in different products. The results of the "Fusariotoxines" project have shown that during milling processes, DON is concentrated in the fractions arising from the outermost parts of the grain, but is also found in finer fractions from more friable parts of the grain. Dehulling processes proved to be more efficient than milling in reducing the amount of DON present in products. Indeed, dehulling was able to eliminate the most contaminated tissues (down to the aleurone layer) without potentially redistributing the finest particles. These studies demonstrated the important role of processes in the potential redistribution of grain mycotoxins in the fractions obtained. Work is ongoing to generate identical findings in bread wheat.
Contamination by Fusarium
Wheat grain is susceptible to contamination by fungi such as Fusarium, which under certain conditions may produce mycotoxins. In wheat, these mycotoxins are mainly trichothecenes, and particularly deoxynivalenol (DON) and its acetylated products. Although European legislation has fixed an acceptable threshold for DON levels in commercial wheat batches (EC Law No. 1881, 2006), it is essential to study how DON is distributed within the grain and if fractionation processes affect the amount of DON present in the different products obtained. This work was carried out in the context of the RARE network programme funded by the French Ministry for Higher Education and Research, focused on mastering the risks of contamination by Fusarium toxins in cereal-based foods. In addition to this study on the fate and distribution of mycotoxins in grain fractionation products, this project also included work on the factors leading to an accumulation of toxins in plants in the field, as well as the specific toxic effects of these substances on animals and humans.
Influence of milling processes on deoxynivalenol (DON) contents
One study concerned the impact of milling processes on the DON content in products resulting from the fractionation of two batches of durum wheat contaminated in the field and displaying contrasting levels of mycotoxins. As the grain batches presented similar characteristics in terms of its texture, size and weight, no significant influence was observed regarding their milling behaviour. It was shown that the DON concentration was highest in bran containing the most peripheral tissues of grains. But although bran and middlings contained half of the total DON, more than 40% were found in total semolina in the least contaminated batch (400 µg/kg). Furthermore, this distribution was reversed in the most contaminated batch (4000 µg/kg). We demonstrated that this rise in DON levels in total semolina from the most contaminated sample was not due to greater contamination in the outer layers, but we were able to show that, during the process, DON became concentrated in the finest particles arising from the most friable parts of the grains.
Thus dehulling of the same batches (which involves the gradual removal of peripheral tissues and does not generate any fine particles during the process) was able to reduce the DON content in grains while enabling the same mass extraction rate. Furthermore, study of the DON content curves, or the monitoring of fungus presence as a function of the extracted mass, demonstrated two phases: an initial phase during which 10% of the mass was removed and when the DON and Fusarium levels fell rapidly, and a second phase when the DON and fungal levels diminished more slowly as the tissues were abraded. These changes to the slopes of the monitoring curves for DON and Fusarium were located in the tissue zone between the testa and the aleurone layer, situated between the pericarp and the starchy endosperm, and revealed thanks to the use of biochemical markers specific to these tissues.
A potential redistribution of mycotoxins during processing
These studies demonstrated the role of processing in the potential redistribution of grain mycotoxins in milling fractions. These results in durum wheat now need to be extended to bread wheat, but preliminary results have shown that, in this case also, milling can contribute to this redistribution. It is also essential to clarify the location and levels of DON in tissues around the aleurone layer and linked to the processes employed, if we wish to better explore the potential nutritional properties of this grain tissue. Furthermore, the Unit is working on the development of pre-treatments that could lower the mycotoxin content in different milling fractions.
Partners
This work was carried out in collaboration with the INRA Mycology and Food Safety Research Unit in Bordeaux (F. Forget) in the context of the RARE Fusariotoxins project referred to above.
Scientific leader
Valérie Lullien,
UMR INRA–CIRAD-SupAgro Montpellier-Université de Montpellier 2
Ingénierie des Agropolymères et Technologies Emergentes
2 place Viala
34060 MONTPELLIER
For further information:
G. Rios. L. Pinson-Gadais, J. Abecassis, N. Zakhia-Rozis, V. Lullien-Pellerin. Assessment of dehulling efficiency to reduce deoxynivalenol and Fusarium level in durum wheat grains. J Cereal Sci. 49, 387-392, 2009.
G. Rios, N. Zakhia-Rozis, M. Chaurand, F. Richard-Forget, M.F. Samson, J. Abecassis, V. Lullien-Pellerin. Impact of durum wheat milling on deoxynivalenol distribution in the outcoming fractions. Food Additives and Contaminants. 26, 487-495, 2009
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