The Sweet Benefit of Giving Olives a Hot Bath | Science News



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Food for Thought

Janet Raloff
Food for Thought

The Sweet Benefit of Giving Olives a Hot Bath

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Many people savor virgin olive oils as they do fine wine. But other people are turned off by the sometimes-bitter overtones of these pricey oils. So, a team of Spanish scientists has just developed a new treatment to sweeten bitter olive oils.

The process is simple: Just bathe olives for a few minutes in hot water prior to pressing out their oil.

The idea for the technique emerged in research reported 4 years ago by José M. García and his colleagues at an agricultural institute in Seville, Spain. They showed that treating olives to the agricultural equivalent of a 2-to-3-day sauna at 40°C (104°F) dramatically reduced the bitterness of oils later pressed from these fruit. However, this processing time was far too long to attract interest from olive oil processors, García notes, so his team upped the temperature to speed the transformation. To do that, the researchers turned to water as the heating element.

Bathing olives for 3 minutes in water that's up to 72°C (about 160°F) achieved the desired drop in bitterness. This brief dip should be easy to accomplish in an olive oil processing plant, García says. His team describes its technique in an upcoming issue of the Journal of Agricultural and Food Chemistry.

Bitter chemistry

Olives contain a bitter compound known as oleuropein. Water-soluble oleuropein isn't part of the oil in olives, but enzymes activated by pressing can transform oleuropein into bitter derivatives that dissolve into the oil. Because heating partially inactivates these enzymes, fewer of the derivatives form and the oil comes out sweeter, García told Science News Online.

Most olive oils on U.S. supermarket shelves are pressed from the fruit and then chemically processed to reduce natural bitterness. The Seville researchers are attempting to create a similar effect without the chemicals. Only oils that avoid the chemical processing may be labeled as "virgin" or "extra virgin."

Through heating, the Seville researchers have been able to reduce the bitterness in virgin oil from a ranking of 4, or strong, to a score of 2, or light bitterness. Because astringency contributes to the characteristic flavor of quality olive oil, García notes that "our object is not the total elimination of bitterness, but a modulating of it."

The researchers found that heating olives boosts their oil's concentrations of two classes of pigments, yellow-orange carotenes and green chlorophylls. The scientists suspect that this is "due to the heat-induced inactivation of the enzymes responsible for pigment degradation during the oil-extraction process." Bottom line: Oils from heat-treated olives should be more deeply hued than ordinary virgin olive oils are.

In terms of health, that might be a good thing. The carotenes responsible for carrots' typically orange hues (see A Carrot Rainbow) not only have vitaminlike attributes, but also can serve as antioxidants—chemicals that quash biologically dangerous reactions in the body. Chlorophylls can be either antioxidants or oxidants. The latter function occurs when chlorophylls are exposed to light, the Seville researchers warn. So, the ultimate antioxidant benefit of these plant pigments will rest with how the oil is stored. A dark bottle would be best.

Nutritionists point out that among fats, olive oil is one of the more beneficial types. A cornerstone of Mediterranean diets, it contains an abundance of heart-healthy monounsaturated fatty acids (SN: 11/21/98, p. 328).

Chefs and gourmands tend to prefer virgin olive oils, especially for salad dressings, sauces, and other recipes in which these oils' deep, fruity flavor can enhance a gustatory experience. However, because all fats are high in calories, even olive oils should be consumed in moderation.


José M. García

Departamento de Fisiología y Tecnología de Productos Vegetales

Instituto de la Grasa (CSIC)

Avda. Padre García Tejero, 4

41012 Seville

Further Reading

Brownlee, C. 2005. Olives alive: Extra-virgin oil has anti-inflammatory properties. Science News 168(Sept. 3):147-148. Available to subscribers at [Go to].

Raloff, J. 2005. Food colorings. Science News 167(Jan. 8):27-29. Available at [Go to].

______. 2004. A carrot rainbow (with recipe). Science News Online (Nov. 20). Available at [Go to].

______. 2003. How olives might enhance potatoes—and strawberries. Science News Online (May 24). Available at [Go to].

______. 1998. High-fat and healthful. Science News 154(Nov. 21):328-330. Available at [Go to].

Seppa, N. 2003. Greek diet reduces inflammatory proteins. Science News 164(Nov. 22):334. Available to subscribers at [Go to].

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