Olive oil waste could play key role in the fight against potato blight

Potato blight is under attack. First a group of German scientists found that the waste products of olive oil production can limit its growth. Now scientists in Scotland are looking at its molecular mode of action.

Olive oil production is a messy business, leaving behind huge amounts of peel, stones and other solids. While the finished product is popular and tasty, these solid residues begin to smell foul as they degrade.

Now German scientists have discovered that after appropriate treatment these residues seem to be suitable for inhibiting dangerous moulds, including that responsible for potato blight.

The breakthrough came while scientists at the University of Bonn were searching for new ways to recycle the undesirable bio waste products of olive oil production. They discovered that the residues have mould inhibiting potential. The project is funded by the aBundesanstalt für Landwirtschaft und Ernährung' (state department of agriculture and nutrition).

The smell associated with olive waste is mainly 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 such as bacteria and moulds.

"The big stink from olive residues can be a long lasting and very intensive experience,“ said Günther Laufenberg, associate professor with the department of food technology at the University of Bonn.

Following his research group's discovery of the inhibiting properties of olive residues, he wondered whether or not those containing polyphenols could be suitable as pesticides for organic agriculture.

Oleuropein is the most important polyphenol in olives. In the plant it works as a self-synthesised abioweapon' against pathogens.

"Freezing the residues or heating them for a short time induces the breakdown of oleuropein into further products which are even more effective,“ added Laufenberg.

It is also possible that the combination of these substances could be the key to success. So the food scientists are also examining how to treat the residues to obtain a concentrated extract from the olive showing improved inhibiting properties. They are also trying to increase the polyphenol yield by using different methods of extraction.

"There are many adjusting screws to be twisted,“ noted Robert Pospiech, one of Laufenberg's co-workers.

To begin with, the researchers freeze or boil the residues. Afterwards they either use ultrasonic treatment to release the polyphenols, or dry and grind it to obtain a fine flour, which can be dissolved easily in alcohol or water.

Results so far are totally different depending on which method is used.

"Of course we prefer environmentally sound solvents and energy-saving extraction methods,“ said Laufenberg. "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 apolyphenol 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 for what to do with the smelly 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. But there was no growth at all observed on the olive residues,“ explained Laufenberg.

However, 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.

The scientists also plan to use their extracts against Phytophtora infestans, the germ causing potato blight.

A blight on spuds

In the middle of the 18th century potato blight destroyed the whole potato harvest in Ireland for several years. The resulting famine reduced the country's population by half as people fled or died of malnutrition.

Phytophtora infestans is still a menace today and worldwide causes over E4 billion of damage. Back in Ireland, the state meteorological office Met Eireann regularly posts blight warnings when weather conditions are favourable for outbreaks.

Despite the huge damage it causes, scientists are only just discovering how the disease infects potato plants.

"In the past Phytophthora infestans was always thought to be a member of the fungal family, but now we know that it is more closely related to golden brown algae, which are commonly known as kelp or seaweed,“ said Pieter van West from the University of Aberdeen's department of molecular and cell biology. "This means that potato blight may have different mechanisms for infecting plants from the way a fungus typically attacks.“

According to the Aberdeen scientists, if they can find the precise molecular methods the blight uses to infect plants, and investigate the properties of the infection structures, then they may be able to target it. This will allow them to develop new disease control and resistance methods without necessarily having to spray the crop with harmful chemicals.

"Potatoes are the world's fourth most important crop plant, so global food security relies on effective control of infestations of potato blight,“ added van West. ""We urgently need to develop alternative crop control measures, including biological control and environmentally friendlier chemicals. Or perhaps even better, we may be able to develop resistant crop varieties through conventional breeding or GM techniques.“

Van West presented a paper aProteomic approaches to investigate the infection process of Phytophthora infestans' in the Eukaryotic Microbiology Group, British Mycological Society and British Society for Medical Mycology joint session of the 153rd Meeting of the Society of General Microbiology at the University of Manchester Institute of Science and Technology in September.

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