Sept. 4 (HealthDay News) -- Fruit may contain more beneficial antioxidants than previously thought, a new international study says.

A study done on apples, peaches and nectarines found these fruits contain up to five times more polyphenols, chemical substances believed to contain disease-fighting properties, than scientists suspected.

Researchers at the Institute of Food Research in Norwich, England, looked at previously ignored nonextractable polyphenols, ones in fruit cells that cannot be broken down and measured as easily as the "extractable polyphenols" that researchers usually study.

"These polyphenols need to be treated with acid to extract them from the cell walls of fruit in the lab," one of the researchers, Sara Arranz from the Spanish Council for Scientific Research in Madrid, said in a news release issued by the food research institute.

"If non-extractable polyphenols are not considered, the levels of beneficial polyphenols such as proanthocyanidins, ellagic acid and catechin are substantially underestimated."

This study appeared online July 28 in the Journal of Agricultural and Food Chemistry.

SOURCE: Institute of Food Research, news release, August 27, 2009