(2007). During all heating period and when held at 90 °C, storage modulus did not decrease indicating resistance to rupture of the flour starch granules. On the other hand, during the cooling period, a sharp increase in the storage modulus was observed of almost double the values reached at the end of the heating period. This indicates that although the gel structure
was formed mainly during the heating period, it was GSK126 further strengthened upon cooling. The TG’inc values were similar in both whole and defatted flours. Therefore, lipids were considered to have no influence in this parameter. Chiotelli and Le Meste (2003) reported that the addition of triglycerides in concentrated potato starch preparations had no effect on the gelatinization process or rheological behavior of starch during heating. On the other hand, G″ was found to be higher than G′ in extruded flours in the whole temperature range studied with no clear TG′inc,, thereby indicating a viscous behavior (Fig. 3C and D). This difference was maintained throughout the cooling period, in which a slight increase in both G′ and G″ is observed during holding at 20 °C. These results are consistent with the DSC data and indicate that there were physical and chemical changes as a consequence of the process conditions.
Similar results were reported by González, Venetoclax Carrarra et al. (2007) who reported a complete loss of the crystalline and granular structure of flours obtained from extrusion cooking. However, Cindio, Gabriele, Pollini, Peressini, and Sensidoni (2002) reported higher storage modulus than loss modulus in extruded cereal mixtures across the entire range of temperature, indicating an elastic behavior. Sandoval et al. (2009) reported the same behavior Lck in a ready-to-eat cereal formulation
obtained by other high temperature processes, and compression molding. The results showed that the chemical composition of the two flours was similar. Flours obtained by both extrusion processes presented high solubility in water and low values of L∗ (luminosity), absorption in water, final viscosity and retrogradation tendency. Three endothermic transitions were observed for whole native amaranth flour that did not change after defatting. Two of them were observed after extrusion in mild conditions and only one after extrusion at severe condition. Viscous behavior, verified by rheology analysis, showed marked differences between native and extruded samples. Extruded flours may be used as an ingredient for instant meal products. Native flour properties are comparable to those of isolated amaranth starch, which are good paste stability, low solubility in water, and elastic behavior. Thus, one of the commercial uses of thermoplastic extrusion is the production of instant meals. The authors are grateful for the financial support from the FAPESP (Process 2007/01907-9).