How Olives Might Enhance Potatoes—and Strawberries

May 22, 2003 at 9:19 am

Many people savor the flavor of olive oil. Few who have ever encountered the “cake” that remains after the oil is pressed, however, savor the experience. Thats because the pressed olive flesh ends up in unused, smelly heaps. In the European Union alone, olive processors produce some 8 million metric tons of these rank wastes each year.

Biotechnologists survey culture dishes as they assess how well olive-derived polyphenols retard the growth of the molds that damage crops. Frank Luerweg, University of Bonn

Polyphenol-treated mold in the dish held by Robert Pospiech (left) shows almost no fungal growth, whereas mold abounds in the untreated dish displayed by Günther Laufenberg (right). Frank Luerweg, University of Bonn

Hoping to mine marketable products from olive waste, Günther Laufenberg and his colleagues at the University of Bonn in Germany were investigating the possibility of extracting flavor compounds. In one experiment, they introduced fungi to the wastes with the expectation that these organisms would help break down molecules and yield the target flavorings. But nothing happened.

No matter what they tried, they couldnt get the fungi to grow. They did a little checking and learned that other food scientists and waste engineers had encountered similar problems: Olive cake resists mold-induced composting and other approaches to natural waste degradation. It was at this point that Laufenberg realized he should change the direction of his research. Indeed, it appeared that he had stumbled onto an organic fungicide that farmers could use safely on food crops.

Over the past few months, the German food technologists have been testing a mixture of olive-waste polyphenols against common crop-damaging fungi. They started by seeding little dishes of a mold-growth medium with various fungi and then added different concentrations of the olive-waste compounds. Depending on the concentration, the polyphenols and their breakdown products severely inhibited the growth of Fusarium culmorum, a wheat blight, and Botrytis cinerea, the so-called gray mold that turns mature strawberries and raspberries to mush and causes blueberries and wine grapes to shrivel and drop.

Even more exciting are preliminary data on the compounds’ ability to fight Phytophtora infestans, the fungus responsible for late potato blight–the black rot that caused the Irish potato famine of the mid-1800s and is still a threat to farmers. The polyphenols appear to protect potatoes the same way they do berries, Laufenberg says.

If these all-natural fungicides live up to their promise, the Bonn team expects the compounds to one day serve as the basis of nontoxic sprays or dusts that farmers could apply to crops even during harvest. Indeed, Laufenberg points out, these natural compounds occur throughout the plant world and are ingested regularly. In fact, theyre among the antioxidants in tea, wine, red fruit juices, and chocolate that may help lower people’s risk of heart disease. Theyre also among the berry pigments that experiments have shown boost memory and other aspects of mental functioning in geriatric animals (SN: 9/18/99, p. 180: https://www.sciencenews.org/sn_arc99/9_18_99/fob2.htm).

The team traced the wastes mold-retarding properties to the polyphenol oleuropein and its two breakdown products, hydroxytyrosol and elenoic acid. As to why olives make oleuropein, the answer is simple, Laufenberg says: To avoid their own attack from molds.

By the way, another advantage shown by the new work is that once the polyphenols are extracted from olive wastes, what remains can be composted to make a potentially rich soil amendment.