Influence of ultrasonic pre-treatment on drying behaviour, energy performance, and quality characteristics of capia pepper cubes under various drying methods

This study investigated the effects of ultrasonic pre-treatment (35 and 53 kHz) on drying kinetics, effective moisture diffusivity, energy performance, colour characteristics, rehydration capacity, microstructure, and thin-layer drying behaviour of cubed capia peppers dried by electrohydrodynamic–hot air (EHD–HA), hot air (HA), freeze drying (FD), microwave (MW), and microwave–hot air (MW–HA). Ultrasonic pre-treatment significantly shortened drying time by increasing effective moisture diffusivity. Among the drying methods, freeze drying required the longest drying time, whereas microwave–hot air drying was the fastest. The Midilli et al. model best described the experimental drying data ( R 2 = 0.9983–0.9998). Freeze drying exhibited the highest energy consumption and specific energy consumption (SEC), whereas microwave-based methods achieved lower energy consumption and higher specific moisture extraction rate (SMER). Drying reduced the L, a, b* , and Chroma values, although EHD–HA, freeze drying, and hot air better preserved colour than microwave-based methods. Freeze-dried samples showed the highest rehydration capacity owing to their highly porous structure. Quantitative ImageJ analysis and SEM observations confirmed that ultrasonic pre-treatment promoted pore formation and microchannel development, facilitating moisture transport and explaining the improvements in drying behaviour and rehydration. Overall, ultrasonic pre-treatment enhanced drying efficiency while maintaining product quality, providing useful guidance for selecting appropriate pre-treatment–drying combinations in industrial applications.