## 4 Comprehensive Review
### A Comprehensive Overview of Bioactive Compounds in Different Food Drying Systems
#### 4.1.2 Radiofrequency  
The dissipation of electromagnetic energy throughout the product reduces the need for thermal conduction or convection, resulting in shorter processing times and minimized quality deterioration [61; 62]. Radiofrequency (RF) is a form of non-ionizing electromagnetic radiation with wavelengths up to 11 m and frequencies between 1 and 300 MHz. These waves can penetrate dielectric materials and generate heat through ionic polarization or dipole rotation. Compared to microwaves, RF waves have a greater penetration depth due to their longer wavelengths [51; 63; 64]. RF heating systems use standard oscillating circuits and include an automatic impedance matching system to maintain a stable coupling power and frequency. DuringRF processing, the moisture content of the material is critical, as it affects the dielectric properties and enhances the heating uniformity [51]. Dielectric properties are material characteristics that determine how a material interacts with an applied electromagnetic field and influence how quickly it heats. Thus, they are a useful way to differentiate good absorbers from poor ones [65]. Radiofrequency drying has been explored in various food products, such as corn kernels [17] and carrots [66]. RF technology is often combined with other novel processing approaches to enhance its effectiveness [67], such as hot air [17; 66], cold plasma [68], or vacuums [65]. Although RF heating offers advantages, such as rapid heating and a deep penetration, it also presents significant challenges when applied to agricultural products. These include overheating at the edges and corners of rectangular samples, non-uniform heating, and arc phenomena due to excess moisture in the RF cavity, which can damage the quality of fruits and vegetables with high water contents, factors that may limit RF's applicability in the food industry [66]. The vacuum-assisted radiofrequency drying (RF-vacuum) of bananas demonstrated advantages in the drying rate and uniformity compared to conventional methods and microwave drying. RF-vacuum drying resulted in a lower final moisture content after 270 min compared to the RF alone. The moisture distribution was more uniform across the banana layers, with the top layer drying faster than the middle and bottom layers, indicating the potential of RF-vacuum drying for more efficient and uniform drying [65]. The findings of [PERSON] et al. [66] also suggest that RFs combined with hot air may be a promising approach for the fluidized bed drying of fresh fruits and vegetables, showing a remarkable performance in improving the heating uniformity in high-moisture foods. Table 4 summarizes the application of this technology in food matrices. [PERSON] et al. [63] suggest that RF drying can be an efficient alternative for preserving the nutritional and sensory quality of food, minimizing the thermal and oxidative degradation compared to hot air drying. However, while RF drying offers advantages, such as reduced thermal stress, it is important to consider its cost-effectiveness and scalability, especially for large-scale industrial applications. Moreover, although RF drying reduces oxidative degradation, it does not completely eliminate the risk of compound loss during the drying