## 2 Thermal Technologies in Food Processing
The temperature in the center of the fastest moving particle depends on the properties of the particles and carrier fluid, particles' velocity and rotation, their residence time distribution (RTD), and characterization of the heat transfer mechanism [21; 22]. The thermal process should be assessed by determination of the heat transfer coefficient (h\({}_{\text{fp}}\)) between the fluid and particle in the continuous flow conditions. The fluid flow field around the solid particle, the thermal and rheological properties of the fluid, and the dimensions of the particle and pipe are key parameters affecting the fluid-to-particle convective heat transfer coefficient (h\({}_{\text{fp}}\)) [17]. The main problem involves the solid particles, especially at the geometrical center position in the product, where sufficient heat treatment or minimum sterilization value should be assured. The particles are hydraulically conveyed through the process equipment in a liquid carrier; hence, it is difficult to measure the temperature in the center of the suspended particles. Therefore, mathematical models should be applied to describe the sterilization process, which are essential for process design and prediction of the particle dynamics and spatial and temporal variations in the temperatures of the particles moving throughout the continuous process system [23]. Ultra-high temperature (UHT) processed and aseptically filled products are described by [24], including products such as liquid dairy products, baby foods, desserts, sauces, soups, fruit juices, and soft drinks. A high heat treatment (135-150 \({}^{\circ}\)C) for a very short time (3-5 s) is carried out followed by aseptic filling into a variety of packaging format, including cardboard cartons, plastic bottles, glass bottles, and foil pouches. Figure 2: Flow diagram of aseptic processing. Large plastic materials or metal drums or large flexible pouches could be alternatively employed. Heat (saturated steam, superheated steam, hot air, mixture of hot air and steam), chemicals (hydrogen peroxide, ozone, chlorine, peracetic acid), irradiation (ionizing rays, ultraviolet, infrared), or a combination of these methods are the methods used to sterilize packages for aseptic processing [25]. Pasteurization is a heat treatment method used to kill pathogenic microorganisms in food, helping to reduce or eliminate pathogens in low and high-moisture foods. Technologies employed to pasteurize low-moisture foods include conventional thermal processes such as baking, roasting, and extrusion, controlled condensation steam processes, and energy-based technologies such as irradiation, radio frequency heating, and cold atmospheric plasma [26]. For the microbial inactivation of high-moisture food such as juices or pulp, the methods exploited include thermal pasteurization, dielectric heating, and microwaves, for example [27; 28; 29]. Pasteurization is a relatively mild heat treatment of food, usually lower than 100 \({}^{\circ}\)C, aimed at destroying the vegetative cells of all pathogenic as well as most nonpathogenic microorganisms. Pasteurization is usually combined with another means of preservation, such as acidity, low water activity, and low-temperature storage [30; 31; 32; 33]. Commercial sterilization is the application of heat (or other appropriate treatment) to free food from any viable form of pathogenic and toxin-forming microorganisms, as well as of non-health significant microorganisms, which could grow in the food under normal conditions of the storage and distribution of the product.