Effect of microwave heating on potato and tapioca starches in water suspension

Abstract

The effects of microwave heating on properties of starch were studied on potato and tapioca starches in water suspension at different temperature (50°C and 60°C). Potato and tapioca starches were adjusted to 30% (w/v) and heat-moisture treated in a microwave oven and conventional heating. Conventional heating was carried out by direct heating the moisture heated sample at 50°C and 60°C while the microwave heating was carried out by microwave oven and the temperature was controlled approximately to 50°C and 60°C. The heated starch samples were analysed for amylose content, pasting properties, swelling and solubility, thermal properties, light microscopy, scanning electron microscopy (SEM) and X-ray diffraction. There were present several changes on physicochemical and functional properties of heated starch for both heating methods. However, microwave method gave higher affect on heating treatment rather than conventional heating. Microwave heating was evidenced in affecting pasting properties of potato and tapioca starches by increase the pasting temperature and the paste stability. Microwave heating also significantly increased the amylose content and swelling power but reduced the solubility and enthalpy of gelatinization (ΔH) of those starches. There were changes in granule structure of starch observed by loss of birefringence and ruptures granule in SEM micrographs in both heating treatment. A change in the X-ray diffraction pattern from B-type to A-type was occurred in potato starch but tapioca starch shows no changes in X-ray pattern.