Analyzing the role that complex phenols and tannins play in human health.

The objective of ongoing European research is to gain an understanding of the biological effects of dietary complex phenols and tannins (CPTs), and their impact on the health and general well-being of consumers. CPTs are found in some vegetables and in many fruits. Red wines and black tea, but not green tea, are particularly important sources of the compounds. Some Europeans consume kilogram quantities of CPTs annually. These are mostly red wine-derived CPTs for southern Europeans and black tea-derived CPTs for northern Europeans. As part of their work, researchers are isolating CPTs from foods, particularly fruit, red wine and black tea. They are analyzing compounds in the diet and studying them using in vitro procedures. The effort involves testing both animals and humans. Investigators are seeking to establish links between consumption of the compounds and the onset of disease.

Most of the attention has focused on isolating CPTs and analyzing them. Condensed tannins have been obtained in quantities not previously available. Approximately 380 g of CPTs characteristic of matured red wine (Cabernet Sauvignon) have been isolated, as has a completely new class of CPTs, named theacitrin, from black tea. The amounts are sufficient to enable the biological effects of the CPTs to be investigated. It is important to have reliable data on the amounts being consumed by different sectors of the population.

Researchers have developed methods for analyzing flavonols, condensed tannins and thearubigins, and data are being accumulated to determine how often these substances occur in foods and beverages. The flavonol and condensed tannin profiles of 17 fruits and beverages have been obtained. The thearubigin content of black tea varies greatly with the brewing method. For example, loose tea leaves in a teapot give more of the compound than does dipping a teabag. Adding milk further complicates the issue as milk proteins remove or bind some of the CPTs.

Further information. M.N. Clifford, Leader, Food Safety Research Group, School of Biological Sciences, University of Surrey, Guildford GU2 5XH, England, U.K.; phone: [phone]; fax: [phone]; email: [e-mail].