Fabricating dehydrated albumen with a novel variable frequency ultrasonic drying method: Drying kinetics, physiochemical and foaming characteristics.

Albumen, primarily composed of ovalbumin, is a vital, nutrient-rich ingredient in the food industry. Drying is a critical step in low-water-activity albumen powder production, allowing extended shelf-life and reduced costs in handling, transportation, and storage of albumen products. Traditional drying methods, such as spray drying (SD) and hot air drying (HAD), often degrade albumen. This study explores variable frequency contact ultrasonic drying (CUD) as a novel and green alternative, operating at a central frequency of 20 kHz with sound amplitudes of 0 %, 40 %, and 60 %, and temperatures of 40 °C and 60 °C. The drying kinetics, physical, and foaming properties of CUD-dried albumen proteins were compared with those of hot-air-, spray-, and freeze-dried (FD) samples. Compared to HAD, CUD significantly enhanced the drying process, as evidenced by a 240 % increase in effective moisture diffusivity, a 66-78 % reduction in activation energy (Ea), and a 27 % reduction in drying time. Moreover, CUD maintained higher protein integrity, evident from a 24-35 % decrease in enthalpies, more β-turn and random coil structures, and increased free sulfhydryl groups. Notably, CUD at 40 °C significantly improved foaming capacity by 88 %, and at 60 °C, it enhanced foaming stability by 34 %, outperforming other drying methods. Protein solubility of CUD-albumen was improved by 10-12 % compared to HAD and was slightly better than FD. CUD-albumen showed a brighter color with a 26 % lower browning index than the HAD samples. Overall, CUD emerges as an effective and sustainable method for drying high-protein materials, ensuring high-quality albumen powders.