28 Aug 2009 --- An international team of scientists has found that the polyphenol content of fruits has been underestimated.

Polyphenol content in fruits usually refers to extractable polyphenols, but a Spanish scientist working at the Institute of Food Research in Norwich analysed apple, peach and nectarine. She found that nonextractable polyphenol content is up to five times higher than extractable compounds. This work has been published in the Journal of Agricultural and Food Chemistry.

“These polyphenols need to be treated with acid to extract them from the cell walls of fruit in the lab,” said Sara Arranz from the Spanish Council for Scientific Research (CSIC) in Madrid. “If non-extractable polyphenols are not considered, the levels of beneficial polyphenols such as proanthocyanidins, ellagic acid and catechin are substantially underestimated.”

Dr Paul Kroon from IFR explains: “In the human body these compounds will be fermented by bacteria in the colon, creating metabolites that may be beneficial, for example with antioxidant activity.”

The Spanish research group, led by Professor Fulgencio Saura-Calixto, has been working to show that nonextractable polyphenols, which mostly escape analysis and are not usually considered in nutritional studies, are a major part of bioactive compounds in the diet.

“These polyphenols are major constituents of the human diet with important health properties. To consider them in nutritional and epidemiological research may be useful for a better understanding of the effects of plant foods in health,” says Professor Saura-Calixto.

The study was funded by a scholarship to Dr Arranz from the Spanish Ministry of Science and through IFR’s core strategic grant from the Biotechnology and Biological Sciences Research Council.

Full bibliographic information: High Contents of Nonextractable Polyphenols in Fruits Suggest That Polyphenol Contents of Plant Foods Have Been Underestimated'. Sara Arranz, Fulgencio Saura-Calixto, Shika Shaha, Paul A. Kroon. Journal of Agricultural and Food Chemistry 2009 57 (16), 7298-7303.