Modeling Mass Transfer Kinetics and Thermodynamic Properties of Ultrasonically Pretreated and Untreated Apple Slices During Air-Frying

The combination of pretreatment with ultrasonic technology and air-frying could improve the quality and efficiency of apple slice processing. This research aimed to explore how ultrasonic treatment prior to frying and varying temperatures during air-frying impact the drying and thermodynamic characteristics of apple slices. The study also aimed to assess mathematical models that explain the moisture transfer kinetics and to numerically simulate the moisture distribution in apple slices during air-frying operation. The results revealed that the moisture content and water activity (a_w) of apple slices consistently decreased with longer frying times, regardless of the temperature. The mathematical models' precision was confirmed through regression analysis, which accurately represented the dynamics of moisture transfer, activation energy (E_a), and Gibbs free energy (ΔG) throughout the frying process. The results of the statistical analysis showed that the two-term (exponential) model was effective in predicting moisture transfer in apple slices throughout air-frying process, while the spatial distribution of moisture was successfully illustrated by the diffusion model under different conditions. Additionally, numerical simulations showed that moisture removal is faster at higher frying temperatures, and ultrasonic pretreatment led to a shorter frying time. Ultrasonic pretreatment combined with higher frying temperatures led to reduced differential enthalpy, along with an increased effective moisture diffusivity and Gibbs free energy difference. These findings are essential for improving and optimizing the frying process in food manufacturing.