Arabinoxylan of varied structural features distinctively affects the functional and in vitro digestibility of wheat starch

This study explored the effects of wheat bran arabinoxylan (AX) of various molecular structures on the functional and in vitro digestibility of wheat starch. AX was separated with sequential ethanol precipitation into different fractions (L-Fra and H-Fra), followed by acidic treatment at varied time to convert L-Fra into different sub-fractions (H-Sub, M-Sub and L-Sub), and the structural features of AX and its subsequent fractions were compared. The Mw and branching degree of the fractions were decreased in the order of H-Fra (545 kDa, 1.15), L-Fra (86 kDa, 0.35), H-Sub (38 kDa, 0.16), M-Sub (21 kDa, 0.10) and L-Sub (7 kDa, 0.08). The functional properties, such as pasting properties, rheological properties, thermal properties, and their effect on the in vitro digestibility of wheat starch-AX combinations, were closely related to the molecular structures of AX. AX with higher Mw, higher branching degree and phenolic content could better inhibit the starch gelatinization and retrogradation, thus reducing the apparent viscosity and gelling properties of wheat starch. The possible mechanisms can be illustrated as 1) AX could compete for water with starch to inhibit granule expansion; 2) AX could not only adsorb on the surface of starch granules through hydrogen bonds but also entangle with the leached amylose and wrap on the surface of granules; 3) AX contained phenols, leading them to inhibit granule expansion through non-covalent interactions with starch molecules. Overall, this study provides a theoretical basis to improve the quality of wheat starch foods and extend the shelf life of wheat foods.