Physical and thermal properties and X-ray diffraction of corn flour systems as affected by whole grain wheat flour and extrusion conditions
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Starch gelatinization is one of the most important transformations during the extrusion process. The objective of this study was to investigate the effect of extrusion variables (feed moisture (FM) and temperature) and the incorporation of whole grain wheat flour (WGWF) on the specific mechanical energy (SME) of the system and some of the properties related to starch changes (water absorption index (WAI), water solubility index (WSI), thermal properties, and X-ray diffraction properties) using an experimental design. Non-extruded flour blends were also evaluated. Increasing WGWF and FM decreased both SME and WSI, reflecting decreased extrusion process severity. In extrudates, part of native crystalline structures rearranged from A-type to V-type after extrusion and formation of amylose–lipid complex took place. The differential scanning calorimetry (DSC) curves showed two gelatinization peaks for non-extruded flour blends (56.04–78.25°C) and a third peak at higher temperatures (83.49–100.15°C) attributed to amylose–lipid complex. The extrusion process promoted the complete gelatinization of the starches. The effect of WGWF addition on the thermal properties of the flour blends was noticeable. Starch transformation, as well as its functional properties, studied in flour blends and extrudates were affected by temperature and FM. Thus, despite the technological challenge to include whole grain wheat flour in expanded extruded formulations, maybe the formed amylose–lipid complex formed strengthens the properties of extrudates as functional food.