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residues as pesticides Residue extracts are effective mould inhibitors During the production of olive oils a huge amount of peels, stones and other solid components arises. After appropriate treatment these residues seem to be suitable for inhibiting dangerous moulds. While searching for new recycling ways the undesirable bio waste scientists of the University of Bonn discovered the mould inhibiting potential of the olive residues and could prove it in the lab scale. The project is funded by the "Bundesanstalt für Landwirtschaft und Ernährung" (state department of agriculture and nutrition). Living next door to an olive
grower is not always pleasant: On one hand the final products are popular
and tasty edible oils. But on the other hand the production of olive oils
causes a huge amount of solid residues starting to smell disgustingly
after a while. Mainly it is caused by the high oil and fat content of
the residues. In addition to that olive residues contain polyphenols which
prevent the microbiological breakdown of the residues by preventing propagation
of reducers (bacteria and moulds). Causing a big stink "olive residues
can be a long lasting and very intensive experience" Dr. Laufenberg
from the Department of Food Technology remarks. Experiments using liquid extracts from olive residues to inhibit moulds have already been very effective. For example success could be achieved against the grain pest Fusarium culmorum and by inhibiting the growth of Botrytis cinerea, a grey mould which prefers growing on mature strawberries. Both moulds showed worse growing characteristics on petri dishes containing residue extract in comparison to normal growing conditions. Further field experiments will be realised in summer. The scientists plan to use their extracts against Phytophtora infestans, the germ causing potato rot. In the middle of the 18th century this pest destroyed the whole potato harvest in Ireland for several years. The resulting famine was disastrous, more than a million people died and the resulting mass exodus led two million Irish people to America. Oleuropein is the most important polyphenol in olives. In the plant it works as a self-synthesized "bioweapon" against pathogens. "Freezing the residues or heating it for a short time induces the breakdown of Oleuropein into further products which are even more effective", Dr. Laufenberg says. It is also possible that the combination of these three substances could be the key to success. The food scientists also examine how to treat the residues to obtain a concentrated extract from the olive showing improved inhibiting properties. They also try to increase the polyphenol yield by using different methods of extraction. "There are many adjusting screws to be twisted", Robert Pospiech, a co-worker of Dr. Laufenberg says. The researchers freeze or boil the brown substance. Afterwards they use ultrasonic treatment to release the polyphenols or they dry and grind it to obtain a fine flour, which can be dissolved easily in alcohol or water. Results are totally different referring to each method. "Of course we prefer environmentally sound solvents and energy-saving extraction methods", Dr. Laufenberg says, "any other processing way would only increase costs unnecessarily and entail a worse ecological balance". The scientists hope to be able to develop a kind of "polyphenol varnish", which can be used as a pesticide in the agriculture by spraying it on the fields - being a "natural barrier" against pathogens. Originally the Bonn food scientists had totally different plans what to do with the brown stinky residues. "Our aim was the bioproduction of flavours using oily residues as a suitable substrate." The work should be done by useful moulds and bacteria - similar to the species being involved in the production of sauerkraut. Dr. Günther Laufenberg: "But there was no growth at all to observe on the olive residues." Images referring to this article are available under http://www.uni-bonn.de >> Aktuelles >> Presseinformationen.
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