Hydroxycinnamic acid composition and in vitro antioxidant activity of selected grain fractions

This study was designed to determine the composition in hydroxycinnamic acids and the antioxidant properties of soluble extracts from wheat, rye and buckwheat. Free, soluble and insoluble hydroxycinnamic acids were determined by HPLC-diode array (DAD). Some C-glycosyl flavonoid derivatives were also identified by LC/MS/MS. Total antioxidant capacity, inhibition of lipid peroxidation and scavenging of oxygen radicals were used to evaluate the in vitro antioxidant capacity of the cereal soluble extracts. The highest levels of total hydroxycinnamic acids and derivatives were found in the wheat bran and rye bran fractions whereas the buckwheat flours had only trace quantities of these compounds. The most abundant compound present in the wheat and rye fractions was ferulic acid but small quantities of diferulic acids, sinapic acid, p-coumaric acid and benzoic acid derivatives were also present. The largest proportions of these phenolic compounds were found covalently bound (esters) in the insoluble pellet but between 10% and 30% of the total compounds were solubilized. mostly in water. Most of the antioxidant capacity was found in the water extracts from all the cereal fractions. Overall, buckwheat and wheat germ products exhibited the highest antioxidant capacity whereas the rye products had the lowest antioxidant values. The antioxidant capacity of these complex cereal extracts cannot be explained by simple correlation with the content of total soluble hydroxycinnamic acids. All other soluble compounds present in the extracts, their possible antioxidant activity and interactions need to be elucidated in order to fully explain the final antioxidant capacity of the extracts. (c) 2005 Elsevier Ltd. All rights reserved.