Low-level irradiation and refrigeration of grapes before they are made into wine can magnify the healthful effects of drinking red wine, making a good source of antioxidants two or three times more potent. The finding is reported in the current (October 16) issue of the Journal of Agricultural and Food Chemistry, a monthly peer-reviewed journal of the American Chemical Society, the world's largest scientific society.
Spanish researchers found that low levels of ultraviolet irradiation can significantly boost amounts of resveratrol, according to Francisco Tomas-Barberan, lead researcher from the Spanish Council for Scientific Research in Murcia, Spain. Resveratrol, a compound found in grapes skins that has antioxidant and anticancer properties, is considered largely responsible for the beneficial effects of drinking red wine. The results contradict a previous study that used higher levels of irradiation and grapes picked before they ripened, he said.
Irradiating grapes before they are turned into wine could raise resveratrol levels from one milligram per glass of wine to more than three milligrams, according to the research. High levels of antioxidants like resveratrol protect against the damaging effects of oxygen and nitrogen in the human body, helping prevent high cholesterol, heart disease and Alzheimer's disease.
Though the researchers studied only a Spanish variety known as Napoleon table grapes, the findings can apply to other grapes used to make wine, Tomas-Barberan said. Refrigerating grapes after they are picked can further stimulate the enzymes that produce the healthful effects, he noted.
"By using our treatment, you can increase considerably the resveratrol content of table grapes," he said. "These results show that refrigerated storage and ultraviolet irradiation of grapes can be beneficial in terms of increasing the content of potentially health-promoting compounds."
The researchers analyzed post-harvest ripe grapes exposed to two types of ultraviolet light with different wavelengths. The light appears to activate a natural protection system in the grapes that shields the healthy compounds from damage, Tomas-Barberan said. The same effect has previously been found in apples, cherries and corn. Irradiation has no known side effects, he added.
Elevated levels of resveratrol in red wine are generated during the fermentation process, so the additional benefits of irradiation are less significant for grapes used to make white wine and grape juice, Tomas-Barberan said.
The research cited above was funded by grants from the Spanish government.
The online version of the research paper cited above was initially published September 14 on the journal's Web site. Journalists can arrange access to this site by sending an email to newsroom@acs.org or calling the contact person for this release.
Francisco Tomas-Barberan, Ph.D., is a researcher in the department of food science and technology at the Spanish Council for Scientific Research in Murcia, Spain.
Journal
Journal of Agricultural and Food Chemistry