Macromolecular structure of water-extractable arabinoxylans in endosperm and wholemeal rye breads as factor controlling their extract viscosities

Viscosity is one of the most important attributes of rye-based products related to some health benefits. To identify the factors affecting arabinoxylan-dependent extract viscosity (AX-EV) of rye bread, the structural features of water-extractable arabinoxylans (WE-AXs) and their ammonium sulphate precipitated subfractions were investigated in breads with varied viscosities. Also, an endoxylanase activity in the starting flours was examined. The HPSEC-RI profiles revealed the higher extent of AX depolymerisation in whole-meal bread (WMB) when compared to that in endosperm bread (EB), resulting in its lower AX-EV. This was mostly related to lower molecular weight of the parent WE-AX fraction with distinctly lower proportion of 2-Xylp in the chain. The AX-EV of rye bread decreased with decreasing proportion of AX-I, the major subfraction with 3-Xylp as only branching site. The endoxylanase activity was at least two times lower in endosperm flour than that in WM and negatively correlated with the AX-EV of WMB. The importance of densely substituted AX subfractions with exclusively 2-Xylp and 2,3-Xylp branches, protecting the AX-I from enzymic degradation during bread-making, has been evidenced.