Abstract: This study was undertaken in order to explore the effect and possible mechanism of action of ultrasonic treatment on the gel properties of waxy rice flour. An orthogonal array design was applied to optimize the conditions of ultrasonic treatment based on loss tangent (tan δ) as a measure of gel viscoelasticity. The optimum process parameters were determined as follows: 130 W of ultrasonic power, 20 min of ultrasonic time, and 1:2 of solid-to-liquid ratio. The tan δ value of the rice flour gel treated under the optimized conditions was 0.82. The scanning electron micrographs showed that starch granules in waxy rice flour (WRF) were aggregated and became dispersed after ultrasound treatment. Moreover, the storage modulus (G’), loss modulus (G’’), hardness and springiness of WRF decreased, while the peak viscosity, and adhesiveness rose. The starch content of WRF was 84.34%. Ultrasound treatment had no significant effect on the granular morphology, gelatinization properties, freeze-thaw stability, rheological properties or texture properties of starch from WRF. The structure of proteins from ultrasound-treated WRF was looser with more holes in it, the relative contents of β-sheet and random coil significantly increased, and the disulfide content and the thermal stability significantly decreased as compared to proteins from WRF (P < 0.05). In conclusion, ultrasound treatment can change the gel properties of WRF by changing the conformation of proteins in it.

Key words: waxy rice flour; protein; starch; ultrasonic treatment; gel properties