Microwave-Induced Structural and Functional Changes in Small Granule Starch

Abstract This study investigated the differential effects of controlled microwave treatments on small granule starches (quinoa and amaranth, ~ 2 µm in diameter) compared to regular-sized maize starch (~ 15 µm). Starch suspensions were treated at 25 to 150 ºC for 30 min and at 150 ºC for up to 2 h (with energy inputs of 11.9–472 kJ/g starch) under sealed conditions to prevent moisture loss. Comprehensive structural and functional analyses revealed distinct modification patterns between small and large granule starches. Small granule starches exhibited increasing peak viscosity and gelatinization temperature range below 50 °C, suggesting partial annealing, while no significant changes occurred with maize starch granules. As the temperature increased above 75 °C but below 100 °C, small granule starches showed complete loss of crystallinity, whereas maize starch had a transition from A- to B-type polymorphous structure with 7% decrease in relative crystallinity. Flow behavior analysis identified two distinct types of remnants in the samples, evidenced by inflection points in viscosity profiles. Extended treatment at 150 °C resulted in progressive amylose degradation, showing 67% and 50% decrease in amylose content for maize and quinoa starches respectively after 2 h treatment. The enhanced susceptibility of small granule starches to structural reorganization was attributed to their higher specific surface area and distinct molecular organization. These findings provide insights into the mechanisms of microwave-induced modifications in different starch types and expands potential applications of small granule starches.