Scientists at the University of California, Davis, have identified another group of chemicals in red wine that is linked to the ability to lower cholesterol. Called saponins, these glucose-based plant compounds are being found in an increasing number of foods. This is the first time they've been found in wine, says Andrew Waterhouse, Ph.D., Professor of Enology (wine chemistry) at the University of California, Davis.
His finding was described today at the 226th national meeting of the American Chemical Society, the world's largest scientific society.
For the most part, the so-called French Paradox -- the association between red wine and decreased heart disease -- has been attributed to resveratrol, a compound found in grapes, which acts as an antioxidant. But saponins could be just as important.
"Saponins are a hot new food ingredient. People are just starting to pay attention to it," says study leader Waterhouse. "No one ever thought to look for it in wine."
The compounds are believed to come from the waxy skin of grapes, which dissolve into the wine during its fermentation process. To better understand their distribution in wine, Waterhouse conducted a preliminary study of six varieties of California wines -- four red and two white -- and compared them on the basis of their saponin content.
"Average dietary saponin intake has been estimated at 15 mg, while one glass of red has a total saponin concentration of about half that, making red wine a significant dietary source," the researcher says.
In general, Waterhouse found that red wine contains significantly higher saponin levels than white -- about three to ten times as much. Among the red wines tested, red Zinfandel contained the highest levels. Syrah had the second highest, followed by Pinot noir and Cabernet Sauvignon, which had about the same amount. The white varieties tested, Sauvignon blanc and Chardonnay, contained much less.
Although Merlot was not analyzed in this study, Waterhouse believes it contains significant amounts of saponins at levels comparable to the other red wines.
The study also seems to show a positive correlation between alcohol content and saponin levels. The red Zinfandel tested, which contained the highest level of saponins among all the wines tested, also had the highest level of alcohol, at 16 percent. "We think that alcohol may make the saponins more soluble in wine, but follow up studies are needed," says Waterhouse, who is considered an expert on wine chemistry.
According to Waterhouse, red wines contain about the same amount of saponin as they do resveratrol. But while resveratrol is thought to block cholesterol oxidation by its antioxidant action, saponins are believed to work by binding to and preventing the absorption of cholesterol, he says. He also mentioned that saponins are known to affect inflammation pathways, an effect that could have implications in heart disease and cancer, according to published studies.
Besides wine, other foods containing significant amounts of saponins include olive oil and soybeans. The compounds are even more abundant in desert plants such as the Yucca and Quillaja. For the most part, saponins make up the waxy coating of these plants, where they function primarily for protection.
The University of California-Davis provided funding for this study.
The poster on this research, AGFD 79, will be presented at 8:00 p.m. on Monday, Sept. 8, at the Javits Convention Center, North Pavillion, during the "Sci-Mix" symposium.
Andrew L. Waterhouse, Ph.D., is Professor of Enology at the University of California, Davis.
-- Mark T. Sampson