Effects of ultrasonic and microwave treatment on color, quality and drying characteristics of rice

This study explores the influence of various ultrasound treatment parameters and microwave drying parameters on the quality and drying characteristics of rice. The rice was treated in an ultrasound water bath (200W) for 30 min, 40 min, and 50 min, followed by microwave drying (210W) for 10 min. The influence of ultrasound treatment time on the moisture content variation of rice was found to be significant through correlation analysis. The time required for the 50-min ultrasound treatment to reach the safe moisture level (15 %) was approximately 20 % shorter than the time required for the 30-min ultrasound treatment. Due to the combined ultrasound-microwave treatment, changes occur in the constituents of rice (Starch gelatinization, Maillard reaction, etc.), and the variations in rice quality can be reflected by the changes in CIE Lab color parameters. The differences in characteristic peaks of Fourier Transform Infrared Spectroscopy (FTIR) can reflect the variations in flavor and aroma of rice, as well as the significant disruption of the ordered structure of starch molecules. Additionally, response surface experiments based on Box-Behnken design were conducted to obtain the optimal conditions for ultrasound-microwave combined treatment (240W, 46min, 3min). Moreover, ultrasound-microwave combined treatment leads to a significant reduction in rice hardness and an increase in elasticity.