Impact of high-intensity ultrasound waves on structural, functional, thermal and rheological properties of rice flour and its biopolymers structural features

Physical modifications of flours are an environment-friendly technology receiving increasing attention for widening the range of utilization of these raw materials. Rice flour was modified with ultrasound treatments at a frequency of 24 kHz and varying treatment time (2–60 min) and flour concentration (5–30%) in the dispersion. The effect of the modification was measured in the flours' physical, functional, pasting and rheological properties. Particle size of treated samples was reduced, and particle's disruption was observed by SEM; this had an impact on the water absorption ability, as shown by a sharp increase of swelling power. The thermal properties showed a significant reduction of gelatinization enthalpy, as well as narrowing of the gelatinization temperature range, characteristic of better packed starch crystalline structures after sonication. Modified patterns in starch and proteins were obtained with XRD and FTIR, which indicated impact to their crystalline and amide I secondary structures as a consequence of ultrasonication. Pasting profiles were found to be reduced with increasing treatment time, while higher concentrations did not significantly change the modification achieved. The pasting temperature was found to be significantly increased in all treated samples. Ultrasound treatment led to gels with higher strength, obtaining lower values of tan δ with increasing sonication time and flour concentration. Ultrasound allowed the modulation of rice flour functionality, being the effect independent on the concentration of the treated flour dispersion, up to 30%, and increased by treatment time up to 10 min; for longer treatments not many differences were found.