Viscosity and hydrodynamic radius relationship of high-power ultrasound depolymerised starch pastes with different amylose content

Abstract

Corn starch pastes (5 or 10 w%) with different amylose content (∼2.7%, ∼5.1%, ∼29.6%, or ∼52.7%) were treated using high-power ultrasound (frequency 20 kHz, power 13.5 or 29.9 W) for up to 20 min. Changes in the physical properties were determined using viscosity measurements and dynamic light scattering. Results show that both the viscosity (η) and hydrodynamic radius (RH) decreased markedly with the increase in ultrasound treatment time. FT-IR showed that the molecular scission occurred at the C–O–C bond of α-1,6 glycosidic linkage, and that the extent of breakage was inversely correlated with amylose content. Further, high-amylose starch pastes were found to be more resistant to ultrasound treatment due to their aggregation. A master curve for the behaviour of η and RH is proposed, which is also confirmed by a similar study carried out on the ultrasound treatment of rice starch pastes with different amylose contents. The findings of this work can be used to tailor starch solutions with different viscosities using high-power ultrasound.