Thermal and pasting properties of microwaved corn starch

Corn starch with 15-40% moisture was irradiated at 0.17 or 0.5 W/g for 1 h using the sophisticated Ethos 1600 microwave apparatus that accurately controls temperature and wattage. Temperature of irradiated starch was measured during microwaving. Thermal and pasting properties were studied on dehydrated starch after microwave irradiation. Temperature increases were greatest during the first 10 min for starch at all moisture contents at both microwave power levels. Starch irradiated at 0.17 W/g had a temperature below onset gelatinization temperature (T,,) after 1 h. Higher temperatures were observed for starch with higher moisture content and microwaved at 0.5 W/g. Compared to native starch, starch with 15-40% moisture had higher T-o (measured using differential scanning calorimetry) and with 35-40% moisture had higher peak gelatinization temperature and lower enthalpy change of gelatinization. All paste viscosity parameters measured by the Rapid Visco Analyser were reduced and pasting temperature was elevated for starch irradiated at 0.5 W/g compared to native starch.