Effect of Microwave Treatment on Physicochemical Properties of Maize Flour

Relatively little work has been reported about flour changes during microwave irradiation. For this reason, maize flours were treated by microwave radiation at 400 W for 0.5, 1, 2 and 4 min, and their microstructure and physicochemical characteristics (X-ray diffractometry, differential scanning calorimetry and pasting properties) were analysed. Micrographs showed that maize flour treated by microwave radiation displayed less compacted particles and more swollen starch granules. Treated maize flours displayed higher V-type crystalline structure, indicating amylose-lipid complexes formation. Additionally, onset and peak temperature and gelatinization enthalpy increased when increasing treatment time of samples. Maize flours subjected to mild treatment (0.5 and 1 min) showed higher peak viscosity and breakdown than native maize flour, and maize samples subjected to severe treatments (2 and 4 min) displayed a lower peak viscosity and breakdown, which reflects an increase in shear stability, with respect to native maize sample. In general, microwave treatment fostered changes in starch crystallinity and the formation of amylose-lipid complexes affecting the functional properties of flour such as its pasting behaviour and its thermal properties.