Ultrasound effect on the pre-germination soaking stage of pigmented rice: Impact on nutritional and technological...

In this study, the impact on the pre-germination of red (SCS 120 Rubi) and black (SCS 120 Onix) rice by ultrasound (US) was evaluated before and after the rice soaking step. The efficiency of the US on the pre-germination process was assessed by considering the germination rate and nutritional and technological aspects. For experiments with US, an ultrasonic bath (40 kHz, 18.6 ± 2.3 W L^-1 of power density) was used. The process was optimized using an experimental design containing five variables: solution (ultrasonic bath) temperature, sonication time, rice grain mass, soaking time, and soaking temperature (soaking medium). After the pre-treatment, rice grains were germinated in an incubator at 40 °C for 36 h. For the selected conditions for each cultivar using US, silence conditions (with only magnetic stirring), and control experiments (without US and magnetic stirring) were performed to evaluate the effect of US on grain germination. The best germination rate for both rice cultivars was obtained using US for 5 min (93 %) and 15 min (100 %), respectively. Under these conditions, the germination rate was up to 32 % higher than in the silence and control procedures, demonstrating that the US improved the germination rate. In addition, the best pre-germination procedures using US showed lower fracturability and hardness of rice grains, and a reduction in the cooking time compared to control and silence pre-germination procedures. The use of US did not cause significant changes in the color, luminosity, and nutritional aspects of the rice grains, which is important for the consumers acceptance.