Influence of ultrasonic pre-treatment on drying behaviour, energy performance, and quality characteristics of capia...

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 (R² = 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.