Onion extracts may boost uptake of berry polyphenols: Study
Blood levels of the three select polyphenolic compounds from Nutra Canada’s GlucoPhenol blend of strawberry and cranberry were increased by between 118% and 252% when consumed in combination with the onion extract, report researchers from the Institute of Nutrition and Functional Foods (INAF) at Laval University.
“This study […] highlighted a possible synergistic activity of phenolic compounds for improving bioavailability,” wrote the researchers in the Journal of Agricultural and Food Chemistry. “This work allowed the identification and quantification of actual metabolites generated in vivo following phenolic consumption, as well as the analysis of their pharmacokinetic data which are fundamental to unravel their mechanisms of action.”
The Laval-based scientists performed a rat study and provided doses of phenols that are equivalent to a human intake of 25-333 mg (for a 60 kg person), which is well below the estimated daily human intake of plant phenols of 150-1000 mg.
“The selected doses were lower than the recommended doses in order to be relevant in a nutritional supplementation context and to be further compared with human clinical trials,” they explained.
Obese lab animals had their diets supplemented with a single dose of GlucoPhenol at varying levels or GlucoPhenol plus an onion extract, and had their blood analysed for 21 phenolic metabolites.
“Three glucuronidated conjugates of strawberry–cranberry phenolic compounds, p-hydroxybenzoic acid glucuronide, catechins glucuronide, and methyl catechins glucuronide were found in higher quantities when GlucoPhenol was ingested together with onion extract (+252%, +279%, and +118% respectively), suggesting a possible induction of glucuronidation processes by quercetin,” wrote the researchers.
“This work allowed the characterization of actual phenolic metabolites generated in vivo following a phenolic intake, the analysis of their kinetics and suggested a possible synergistic activity of phenolic compounds for improving bioavailability.”
Source: Journal of Agricultural and Food Chemistry
Published online ahead of print, doi: 10.1021/jf404965z
“Modulation of Strawberry/Cranberry Phenolic Compounds Glucuronidation by Co-Supplementation with Onion: Characterization of Phenolic Metabolites in Rat Plasma Using an Optimized μSPE–UHPLC-MS/MS Method”
Authors: S. Dudonné, P. Dubé, G. Pilon, A. Marette, H. Jacques, J. Weisnagel, Y. Desjardins