Effects of ultrasonic pretreatment and drying approaches on the drying kinetics and rehydration of sprouted mung beans

Sprouting is one of the most traditional methods used to decrease most of the antinutritional elements in legumes. The assistance of ultrasound appears to enhance the drying step of the sprouted legumes. The aim of this study was to examine the influence of ultrasound pretreatment and drying methods (hot-air and infrared) on the drying time, mass transfer kinetic, effective moisture diffusivity (D_eff), and rehydration ratio of sprouted mung beans. The ultrasound process (40 kHz and 150 W) was performed in an ultrasonic bath for 0, 5, 10, 15, and 20 min. The results showed that the ultrasonic pretreatment increased the moisture diffusion capacity (higher moisture loss) and reduced the drying time of sprouted mung beans. Also, the drying time of samples in the infrared dryer was significantly less than that in the hot-air dryer (p < .05). The D_eff determined by Fick's second law was varied from 1.36 × 10⁻¹⁰ to 1.88 × 10⁻¹⁰ m² s⁻¹, and from 1.18 × 10⁻⁹ to 1.85 × 10⁻⁹ m² s⁻¹, for samples dried in hot-air and infrared dryers, respectively. Comparing the coefficient of determination (r), sum of squared error (SSE), and root mean squared error (RMSE) values of 10 models, it was concluded that the Midilli model represents the drying characteristics of sprouted mung beans better than the others. The rehydration ratio of dried samples in hot-air and infrared dryers increased when the ultrasound pretreatment time was increased. In general, the use of ultrasound pretreatment (about 20 min) and an infrared dryer is a promising drying technique for sprouted mung beans with higher mass transfer and a shorter drying time.