Effect of ultrasound pretreatment on the drying kinetics and characteristics of pregelatinized kidney beans based on microwave-assisted drying.

• Different micromave-assisted drying methods can affect the quality of kidney beans. • Ultrasound pretreatment markedly improved drying rate, color and rehydration ability. • Ultrasound processing increased the loss of active compounds. • Functional compounds and amino acid content were affected by different drying methods. • Ultrasound pretreatment produced dried kidney beans with a more porous structure. This study aimed to investigate the effects of ultrasound pretreatment combined with pulse-spouted microwave vacuum drying (PSMVD) and microwave hot air rolling drying (MHARD) on the drying characteristics, microstructure and physicochemical properties of pregelatinized kidney beans. The results showed that ultrasound pretreatment significantly improved the drying efficiency and physical properties of the samples during PSMVD and MHARD, and contributed to the formation of porous structures in the dried beans. Meanwhile, ultrasound promoted the hydrolysis of protein, free amino acids content was significantly increased by 3.69 %–11.4 %. However, the combination of ultrasound pretreatment and drying also resulted in a decreased polyphenolic content and antioxidant capacity of the dried beans. PSMVD with ultrasound for 30 min had the best color (Δ E = 14.17), the shortest drying time (50 min) and had a higher content of amino acids (206.15 mg/g) compared with other products. Overall, ultrasound pretreatment can effectively improve the drying process of kidney beans. [ABSTRACT FROM AUTHOR]