Ultrasound Assisted Hydration of Proso Millet (Panicum miliaceum) Grain

Abstract

Conventional method of hydrating grains is quite time taking and results in quality deterioration of the product hence ultrasound (US) was used to accelerate the process of hydration. In the present study, US (40 kHz, 60 W) has been applied to the grains submerged in water. Post US treatment, the grains were found to reach their saturation limit at 7 hours itself, while in the conventional method, the grains took 26 hours to reach their maximum water imbibition capacity. In each of the cases, the hydration kinetic curve followed a logarithmic-fashioned curve, with the ultrasound-assisted curve (y = 6.3056 In(x) -16.685, R2 = 0.9834) having a higher instantaneous slope than the conventional one (y = 4.3479 In(x) - 11.03, R2 = 0.9926). The observed values were found to best fit the Peleg model (for Control: k1= 0.0431, k2= 7.08352, R 2=0.9933; for US treated: k1= 0.0352, k2= 9.51418, R 2= 0.9684). Acoustic cavitation is a common phenomenon employed in ultrasound treatment, which in turn facilitates the energy transfer to the grain samples through micro-streaming, improving heat and mass transfer, and the abrupt collapse of cavitation bubbles leading to significant pressure and temperature fluctuations in the surrounding region. This mechanism generates free radicals, which further aid in cell membranes' disintegration and micro-channel formation, thereby accelerating the hydration rate.