Application of High-Intensity Ultrasound in Rice-Starch Isolation

High-intensity ultrasound was evaluated as an alternative method to isolate rice starch without the use of chemicals as in the traditional alkaline-steeping method. A rice-flour slurry (flour:water=1:2) was subjected to high-intensity sonication for 15, 30, or 60 min at an amplitude of 25, 50, or 75% and the temperature was controlled at 40 or 50°C. The starch yield ranged from 46.7 to 76.2% (starch dry basis); the protein and damaged starch contents of isolated starches ranged from 0.9 to 1.7% and from 3.1 to 3.5% (dry basis), respectively. The pasting properties of isolated starch as measured by a Rapid Visco-Analyser were affected by the treatment temperature and by the presence of protein and damaged starch contents. The surface of the isolated starch was not damaged by sonication as shown by scanning electron microscopy and the amylose content of isolated starches remained constant after the treatments. Highintensity ultrasound shows a great potential for isolating rice starch in a short period of time without generating alkaline effluent.