Content of antioxidant hydroquinones substituted by β-1,6-linked oligosaccharides in wheat milled fractions, flours and breads

The objective of this study was to quantify seven antioxidant hydroquinones, substituted by β-1,6-linked oligosaccharides, in wheat-based food products by HPLC. These novel compounds were discovered and characterised in our previous study. All seven compounds were quantified in wheat germ and bran. The most abundant compound, 4-hydroxy-3-methoxyphenyl β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranoside, was present at 6.3 g/kg in germ and 0.7 g/kg in bran. In whole-wheat grains, as well as in several kinds of wheat flour and wheat bread, these antioxidants were present at much lower concentrations; only two of them could be quantified. None of these compounds were detected in low-protein flour mixture. Their total content in analysed wheat products decreased in the following order: germ > bran > whole grains ∼ whole grain flours > refined flours > refined bread ≫ low-protein flour mixture. It correlated well with the antioxidant capacity of water–ethanol extracts of these products determined by Trolox equivalent antioxidant capacity (TEAC) assay (r2 = 0.984). The contribution of the analysed compounds to the total antioxidant capacity of wheat germ extract was 52%, whereas the contribution of the most abundant compound was 38%.