Ultrasound technology enhances the hydration of corn kernels without affecting their starch properties

Abstract

This work studied the effects of ultrasound treatment on the process of hydration of corn kernels, evaluating both the water uptake and its starch properties. For that, an ultrasound bath at a frequency of 25 kHz and volumetric power of 41 W/L was used. Furthermore, different treatments were applied in order to determine the mechanisms of enhancement of the hydration process (direct or indirect effects), by studying the hydration kinetics and the microstructure of the kernels. Finally, the rheological, thermal and structural properties of the starch extracted from the corn kernels (hydrated with and without ultrasound) were evaluated. Due to the particular behavior of the corn kernels during hydration, a two terms semi-empirical equation was proposed to explain the process, which contains two simultaneous ways related to the different mechanisms of water influx. Ultrasound significantly improved the hydration process, increasing water uptake and decreasing the process time by ∼35%. In contrast to other grains, it was demonstrated that the enhancement of the process was only due to the direct effects (inertial flow and sponge effect) and not the indirect effects (micro-channels formation). Finally, it was demonstrated that the ultrasound treatment did not alter the properties of the starch. As a conclusion, it was shown that the corn kernels can be quickly hydrated using ultrasound treatment without modifying any of the properties of the starch, this being highly desirable for the starch industry.