Effects of superheated steam on starch structure and physicochemical properties of buckwheat flour during storage

This study showed that superheated steam (SS) processing could inhibit the changes in physicochemical properties of buckwheat during storage by altering the molecular structure of starch. The relationship between the molecular structure of starch (granular morphology, chain-length distribution, molecular weight, and long- and short-range structures) and the physicochemical properties (swelling power, water solubility, thermal properties and pasting properties) of flour and starch were investigated. The results showed that the water solubility, onset temperature (T-o), gelatinization enthalpy (Delta H), and pasting viscosity (peak, trough, and final) of untreated buckwheat flour decreased during storage, while the gelatinization temperature range (T-c-T-o) increased significantly (P < 0.05). SS processing restricted these changes in the physicochemical properties based on the results of the less reduction in relative crystallinity and 1047/1022 cm(-1) ratio of starch. Furthermore, SS processing increased the mobility and reassembly of starch chains, narrowed the amylopectin branch chain-length distribution, reduced the heterogeneous molecular weight distribution, and increased the thermal stability of starch. Consequently, fewer changes were evident in the Delta H and breakdown value of the buckwheat flour during storage. Pearson's correlation analysis verified the relationship between the physicochemical properties of the buckwheat flour and the SS-induced changes in the starch molecular structure.