## 2 The Main Thermal and Non-Thermal Processing Techniques
### Non-Thermal Processing  
Food processing technologies that do not use direct heating as the main means to inactivate microorganisms and enzymes in food products are broadly recognised as non-thermal technologies. Non-thermal technologies are often classified as technologies that are capable of achieving microbial inactivation at sub lethal temperature. Contrary to thermal technologies, non-thermal processing has minimal effects on the texture, color, aroma, taste, and nutritional value of food products while achieving food objectives and meeting consumer demands for fresh-like, minimally processed, and preservative-free foods. Non-thermal techniques including high pressure processing (HPP), ultrasound, pulsed electric field (PEF), and cold atmospheric plasma (CAP) as well as packagingtechnology, particularly modified atmospheric packaging (MAP) have been exploited for niche applications in muscle food processing. In the muscle food processing, HPP involving pressures in the range of 100-600 MPa is mainly employed to extend shelf-life, improve the food safety profile, and to alter key quality parameters, including texture, color, and water holding capacity of muscle food products [75,76]. The inactivation effects of HPP on microorganisms including yeasts, molds and bacteria and spores and shelf life extension of muscle food products are well documented in the literature (Table 2). The general inactivation mechanism of microorganisms by HPP is associated with a combination of several factors including changes in the cell membranes, cell wall, proteins, and enzyme-mediated cellular functions [77,78]. More recent studies have reported that the HPP treatment could improve tenderness and eating quality of meat [79,80]. Further, HPP can be employed to obtain a better texture and appearance for gels and gel-like fish products. High pressure shift, assisted or induced freezing and/or thawing of fish products can extend the shelf-life of frozen muscle food products while minimizing the adverse effects of freezing technology on the quality parameters [81, 82, 83]. Power ultrasound processing has emerged as an alternative non-thermal food processing technique for a range of applications. In the meat processing, ultrasound has shown potential for meat tenderization, acceleration of maturation and mass transfer, and shelf life extension of muscle products [84]. Additionally, ultrasound can assist in reducing salt usage in processed meats [85] and improve the emulsification and gelling properties, thus may allow reduction in usage of chemical additives such as phosphates [86]. Several studies have proven that the ultrasound can reduce brining time without affecting meat quality, whilst improving salt diffusion rates [87]. These ultrasonic effects can be explained by combination of cavitation phenomena, shear disruption, localized heating, and free radicals' formation. CAP is a novel non-thermal technology which is effective against a wide range of microorganisms, including pathogens, spoilage bacteria, biofilms, and bacterial spores commonly associated with various foods including muscle food products. Plasma is composed of highly reactive species, including gas molecules, primarily composed of photons, ions and free electrons, neutral particles (atoms, molecules), activated and metastable species (NOx\(-\)), free radicals like reactive oxygen species (ROS), and reactive nitrogen species (RNS), which collectively attribute to its bactericidal properties. The plasma technique has recently been tested for surface decontamination on a range of muscle foods (Table 2). Recently, plasma has been reported as a novel source of nitrite, which is an important additive in the production of cured meat products [88]. PEF processing involves the application of short-time electric pulses causing permeabilization of cells, thus inducing several effects. Microstructural modifications in muscle foods after PEF treatment can improve techno functional properties such as water holding capacity and tenderness of the treated products [89].