## 2 Thermal Technologies in Food Processing  
_Pasteurization, Sterilization, and Aseptic Packaging_  
One of the most important unit operations in food processing is thermal processing. Food preservation depends on major food operations, such as canning, pasteurization, and sterilization, in order to destroy pathogenic bacteria. Conventional in-container thermal processing involves the hermetical canning of food followed by heat treatment for a specific time-temperature in order to inactive pathogenic bacteria growth and extend the product shelf life with minimum quality deterioration. Examples are high-temperature short time (HTST), low-temperature long time (LTLT) or ultra-high temperature (UHT). Seal integrity, sufficient process lethality, and post-process hygiene are the most important factors to be considered in thermal processing. A hermetic seal brings seal integrity, thus helping in preventing recontamination and creating an environment inside the container that prevents the growth of other microorganisms of higher heat resistance. It also helps in preventing toxin production from pathogens. The time-temperature schedule for the required process lethality should be effective to eliminate the most heat-resistant mesophilic anaerobic spore-forming pathogen _Clostidium botulinum_. Aseptic processing being an alternative thermal food processing and packaging technique involves the packaging of commercially thermally sterilized products into sterilized containers and then sterile sealing under sterile conditions to prevent microbial product recontamination [15]. However, we should stress out that this process cannot stand alone, since it does require one of the thermal processes (pasteurization or sterilization) prior to aseptic packaging. Aseptic systems use ultra-high-temperature (UHT) sterilization, which is a fast heating treatment at temperatures higher than pasteurization temperatures. A typical aseptic process involves receiving a food material, in-flow heating, holding at a sufficient time for sterilization, and cooling down in order to fill it in. Containers are usually pre-sterilized and quality checked. Then, filling and hermetic sealing follows in aseptic containers, as shown in Figure 2[16; 17]. In aseptic filling, the food product and the package are continuously sterilized separately and then meet in the aseptic filler, which has a sterile environment, and this makes it different to other traditional methods of food packaging. A high rate of microbial destruction and improved product quality, such as better texture, flavor, and color, is achieved with aseptic processing compared to traditional thermal processes, such as canning. The benefits of aseptic processed foods are attractive and include a higher shelf life, better nutritional and sensory properties, and wider packaging sizes and container materials [18]. The design for aseptic processing varies for different foods. There is a demand for aseptic processing of low acid food (pH > 4.6) and high-viscous food containing discrete particles. Aseptic processing design for heterogeneous food products (liquid-particulate food) is more complicated and challenging [19] due to irregular solids' particle size distribution, different residence times, the temperature measurements of moving particles, and the estimation of convective heat transfer coefficients at the particle surface. The lethality value (F\({}_{0}\)) of an aseptic processing in food is used to quantify target spore inactivation in the sterilization process. Design of the aseptic food processing system should include heat and hold (sterilization) of every particle of food product for at least the minimum time specified in the process [20]. Commercial sterility needs to be accomplished in the coldest location (normally, center) of the fastest moving particle.