Effect of Microwave Treatment on Physicochemical Properties of Maize Flour

Abstract

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.

Inactivation of Endogenous Rice Flour β-Glucanase by Microwave Radiation and Impact on Physico-chemical Properties of the Treated Flour

“…The only significant effect (p < 0.01) was obtained in the gelatinization peak temperature (weak annealing, Biliaderis 2009), although the quantitative importance of this change was rather minor. Other authors have also reported an increase in the gelatinization peak temperatures of microwave-treated 30 % moistened maize flours (Roman et al 2015) when MW energy was applied for 2 and 4 min; the increases observed by these authors were~3°C, while that of the present work was less than 1°C. Lewandowicz et al (2000) also observed rises in the gelatinization peak temperatures of 30 % moistened starches treated by MW for 60 min at 0.5 W/g, that varied from 13°C for wheat to 6°C for waxy corn starch, in comparison to their untreated counterparts.…”

“…Other authors also found a reduction in starch gelatinization enthalpy for MW-treated corn starches (Luo et al 2006;Stevenson et al 2005). In contrast, Roman et al (2015) have reported an almost double gelatinization enthalpy of all MW-treated corn flour samples with respect to the native one. Consequently, the extent of MW heating effects on thermal behavior of granular starches depends on the starch source, the amylose and moisture content, as well as the intensity and time of the applied microwave treatment (Zavareze and Dias 2011).…”

“…Indeed, the A-type crystalline pattern was conserved in the MW-treated flours with 25 %, for any processing time (0.67, 1, 2, and 4 min), and no significant differences in the relative crystallinity value compared to the native flour (starch) were observed. Luo et al (2006) and Roman et al (2015) reported an increase in x-ray intensities for microwave-treated maize starch and flour, respectively. It has been postulated that microwave radiation can lead to formation of additional double helical structures within the starch crystallites, leading to a higher molecular order than that in native starch (Luo et al 2006).…”

“…They have reported that HMT promotes additional amylose-amylose and/or amylopectin-amylopectin chain interactions, which restrict amylose leaching and decrease retrogradation events. A recent study by Roman et al (2015) reports on the effects of short-time (0.5 to 4 min) MW treatments of corn flours at 30 % moisture. They found opposite effects on pasting properties depending on the MW treatment time.…”

“…A decrease of the maximum (peak) viscosity was also observed by Pinkrová et al (2003) by increasing temperature of microwave treatment of the rice grain and increasing power output at a moisture content of 30 %. Roman et al (2015) have examined the effect of MW on flour structure. They found a more disaggregated structure and a less compact matrix, with starch granules being more naked and slightly swollen.…”