Microwave foaming of starch-based materials (II) thermo-mechanical performance

Abstract

The thermo-mechanical performance of extruded wheat starch/flour containing different additives was examined via microwave-heated thermo-mechanical analysis. Additionally, the dielectric property of the wheat starch-based materials was also studied using a microwave calorimeter. It has been found that when glycerol or polyvinyl alcohol was used as single additive in wheat starch, a content limit existed and using the additives at a concentration higher than the limit will lead to deterioration of the material’s microwave foamability. A good initial thermal expansion is essential for a proper foaming of the wheat starch-based materials; however, high enough dielectric loss factor (ɛ″) is also required for the formation of foam structure under microwave radiation. Glass transition temperature ( Tg) for the extruded wheat starch materials was detected by microwave thermo-mechanical analysis at about 75–95°C when heated at 15°C/min; and for the foamable formulations, the foaming temperature ( Tf) is generally 10–20°C higher than the corresponding Tg. Impurities like proteins play important roles in the microwave foaming of extruded wheat flour. Overall, the extruded wheat flour with additives is more difficult to foam under microwave heating than the wheat starch extruded from the similar formulations.