Effect of popping water content and amylose/amylopectin ratio on the physical properties of expanded starch products with different shear histories

Abstract

Aerated starch products are a staple of the food industry, with particular relevance in the snack market. Water plays a crucial role in the formation of such products due to its utility both as a blowing agent and as a starch plasticiser. Amylose/amylopectin ratio and shear are traditionally also important factors in starch expansion. In this study, waxy, normal and high amylose maize starch variants were expanded using a rice-cake style popping head at water contents between 0% and 24%. This range of water contents was achieved by drying the material at 105 °C and then rehydrating by suspension over water at 50 °C until the desired water content was reached prior to popping. Sample types were further subdivided into low shear (native) and high shear (extruded) processing prior to popping. Processing history, amylose content and water content all influenced the water interaction properties of the popped products. However, density was largely governed by water content with little apparent influence of other factors. An optimum water content range to produce low-density (and therefore high desirability in industry) products was identified in the region of ~15–21% water. Samples popped below this range exhibited suboptimal expansion whilst those popped at higher water contents experienced violent blowout.