## 1 Introduction  
Drying is an important process in the food industry as it enables the extension of the shelf life of food products as a consequence of the decrease in the material's water activity. The most common drying method is the convective one. While convective drying offers numerous benefits, it can be a lengthy and energy-intensive method that often requires high-temperature conditions. The application of pre-treatments and additional drying techniques allows for a decrease in the negative impact of convective drying on plant tissue and enables the selection of optimal process parameters [1]. Ultrasound (US) is among the well-documented non-thermal pre-treatment methods employed in the food industry. Ultrasound waves are characterized by frequencies above 20 kHz. Depending on the wave frequency, intensity, and ultrasound application, the passive and active implementation of sonication are distinguished: (a) waves of low intensity at high frequencies reaching values above 100 kHz, which, due to their non-invasive impact, are used in food quality control and diagnostics; (b) waves of high intensity with frequencies ranging from 20 kHz to 100 kHz, which have been implemented in food processing to modify food properties. As a result of the formation of cavitation bubbles that penetrate the material at very high velocity (up to 200 m/s), microscopic tunnels appear, influencing the course of drying as the internal structure changes [1; 2]. Most studies in the literature focus on US pre-treatment or US-assisted drying separately; this study uniquely integrates both and optimizes parameters holistically. Generally, US pre-treatment changes the biochemical, physical, and mechanical properties of the studied material; thus, as aforementioned, it directly impacts further processing. There are many examples in the literature of the application of ultrasound before drying and their positive influence on shortening the drying time and product quality. [PERSON] et al. [3], [PERSON] et al. [4], and [PERSON] et al. [5] reported reduced drying times of walnut kernel, basil, and mulberry leaves, respectively, after ultrasound pre-treatment. Moreover, ultrasound pre-treatment was utilized to enhance the extraction of bioactive compounds, resulting in compounds that exhibit antioxidant, antimicrobial, anti-inflammatory, or anticancer properties [6]. Additionally, it has been reported that sonication, in combination with other treatments, can lead to the inactivation of potentially health-threatening microorganisms [7]. [PERSON] et al. [8] studied the influence of ultrasound combined with cold plasma on microbes and observed their synergistic effect, whereas [PERSON] et al. [9] noted the inactivation of _Salmonella typhimurium_ in liquid whole eggs after the application of ultrasound with lysosome. It should be noted that ultrasound pre-treatment is not the single application of sonication, as ultrasound is implemented during the drying process as well. Employing ultrasound technology during the drying process can greatly lower the drying temperature, minimize the drying duration, decrease energy usage, and enhance the quality of the dried product. This method helps maintain important nutrients (such as vitamins and minerals) and preserves the appearance (shape and color) of the materials. [10]. [PERSON] et al. [11] reported the shortening drying time and reduction in energy consumption during the convective drying of green peppers subjected to ultrasound with a power of 100 W and 200 W, by 32% and 37% and by 8.7% and 10.7%, respectively. Moreover, the use of sonication also had a positive effect on the final product's quality. The sonicated samples contained approximately 18 and 25% more vitamin C, respectively, than the control ones did. The water activity decreased down to 0.32 and 0.29, respectively, which provided better protection against microbiological changes in the material, compared to the material not treated with ultrasound (water activity of 0.42).