Developing ultrasound-assisted hot-air and infrared drying technology for sweet potatoes

The influence of ultrasound (US) pretreatments combined with infrared (IRD) and hot-air (HAD) drying on drying kinetics, mathematical modeling, bioactive compounds (antioxidant activities, Vitamin C, phenolics, and flavonoid contents), qualitative properties (β-carotene, total carotenoids, color indexes, textural profile), enzyme inactivation, and exergetic analysis of sweet potatoes. The US pretreatment at 40 kHz combined with IRD and HAD (70 °C) significantly lessened the drying time and water contents. Besides, it did not affect the sweet potato's bioactive components and other quality-related attributes. The samples' activation energy (E_a) ranged from 17.60 to 29.86 kJ/mol for both dryers, with R² (0.999-0.9809). Control samples had the highest specific energy consumption (SEC) due to the extended drying period, whereas ultrasound (40 kHz) treated samples had the lowest SEC during HAD and IRD at 80 °C. The thermodynamic parameters indicated that increasing the drying temperature lowers the enthalpy and Gibbs free energy, while entropy resulted in negative values. HAD had better textural qualities (hardness and resilience). The US pretreatments followed by HAD or IRD may lead to an energy-efficient method with acceptable quality maintenance.