Morphology, pasting and thermal properties of microwave-assisted cassava starch-stearic acid complex

Abstract

In this study, the physicochemical properties of microwave-assisted cassava starch-stearic acid complex was investigated. The effects of the modification methods were assessed using a scanning electron microscope, differential scanning calorimeter and rapid visco analyser. Native cassava starch showed mostly polygonal shape with some granules irregular and round in shape. Native cassava starch with added stearic acid had slight changes in shape while microwaved cassava starch showed irregular and dented granules with pin-holes or fissures. Native cassava starch modified with stearic acid alone or microwaved cassava starch with added stearic acid showed decreased swelling power as compared to the native starch. Pasting properties of cassava starch were significantly affected by stearic acid addition or microwaving. Stearic acid addition alone reduced the peak viscosity slightly (approx. 7%), adding stearic acid to microwaved cassava starch reduced the peak viscosity by approximately 9%, while microwaving cassava starch-stearic acid mixture showed greater reduction in peak viscosity (approx. 19%). Pasting of native or microwaved cassava starch with stearic acid resulted in the formation of type I amylose-lipid complexes, with melting temperatures ranging from approx. 92 to 102oC. Microwaving can improve complexation of stearic acid with cassava starch to produce modified starch with higher thermal stability and increased final viscosity.