We may be underestimating the antioxidant content of fruit and vegetables, according to an international team of scientists from Spain and the UK.
While the polyphenol content of fruits usually refers to extractable polyphenols, new research published in the Journal of Agricultural and Food Chemistry reports that the non-extractable polyphenol content is up to five times higher than extractable compounds.
According to studies with apple, peach and nectarine, previous measures to quantify polyphenols may have been limited by the extraction technique.
"These [non-extractable] polyphenols need to be treated with acid to extract them from the cell walls of fruit in the lab," said lead author 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."
In collaboration with the Institute of Food Research in the UK, Arranz states that this represents the first report on using methanol and sulfuric acid to analyse the non-extractable polyphenol content of apples, peaches, and nectarines.
"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," said Paul Kroon from IFR.
Knowledge of the contributions of such compounds is important, suggest he researchers, since non-extractable polyphenols are not usually considered in nutritional studies, but are actually 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," said the study’s leader, Professor Fulgencio Saura-Calixto.
Source: Journal of Agricultural and Food Chemistry
Volume 57, Issue 16, Pages 7298-7303, doi: 10.1021/jf9016652
“High Contents of Nonextractable Polyphenols in Fruits Suggest That Polyphenol Contents of Plant Foods Have Been Underestimated”
Authors: S. Arranz, F. Saura-Calixto, S. Shaha, P.A. Kroon