Effect of moisture content, temperature, and absolute expansion ratio on the effective moisture diffusivity of swell-dried carrots and apples

In this study, the swell-drying process of apples and carrots, which involves combining the Instant Controlled Pressure Drop (DIC) operation with airflow drying, was carried out at an airflow velocity of 5 m·s⁻¹ and at temperatures of 40, 50, and 60 °C. Under these conditions, the effective moisture diffusivity of the product was determined based on the Coupled Washing/Diffusion (CWD) model. Experimental results showed that the effective diffusivity of all DIC-treated samples increased compared to the raw material, with the highest increase being approximately 5.7 times. The effective diffusivity was found to depend on moisture content, temperature, and the absolute expansion ratio, as shown by an empirical model with an R-squared value of 67.32% for apples and 60.15% for carrots. Investigation of the effects of DIC treatment on bulk density, intrinsic density, and absolute expansion ratio showed that both steam pressure and heat treatment time significantly affected carrots, while steam pressure was the primary factor influencing apples. The regression equations for these physical properties were also obtained, with R-squared values ranging from 77.75% to 93.82%.