Effect of Incorporating White, Red or Black Quinoa Flours on Free and Bound Polyphenol Content, Antioxidant Activity and Colour of Bread

Abstract

Interest in quinoa as a functional food ingredient is currently emerging. The flours from white, red and black quinoa seeds were analysed in terms of total polyphenol content and antioxidant activity. They were incorporated at 25% on flour basis into the bread dough formula to evaluate their potential to improve the functional properties of wheat breads. The contribution of extractable polyphenols (soluble forms) and the largely unexplored hydrolysable polyphenols (bound forms that can be found in the residues of the former) were taken into account to reflect a realistic health-promoting potential of breads. The red and black quinoa varieties stood out compared to wheat flour, with about double the polyphenol content and up to 4.7-fold increments in antioxidant activity when considering the sum of extractable and hydrolysable polyphenols. The red and black flours were equally effective in intensifying the antioxidant properties of bread despite the baking process (between 2- and 3-fold). They produced significant changes in the parameters that describe crust and crumb colour (L*, a*, b*). A clear darkening was observed compared to the control bread, an appealing attribute for lovers of unconventional and natural products. According to our results, the flours from the coloured quinoa seeds could be considered interesting antioxidant sources and be applied as natural ingredients in bread-making; new, promising and valuable unconventional products for consumers and producers could be developed.