## 2 The Main Thermal and Non-Thermal Processing Techniques
### Thermal Processing
The electromagnetic waves produced inside the microwave oven cause water molecules in the food to vibrate, producing heat [14; 19]. Several studies have reported that the performance of microwave heating overpasses that of traditional heating methods. For example, a recent study showed that microwaving chicken thigh and breast meats results in better quality attributes of the cooked products compared to conventional ovens [63]. In another study, microwave cooking was found to improve saltiness perception of grass carp meat, with lower cooking loss and shear force being observed compared to traditional water bath [64]. However, it is well-known that nonuniform temperature distribution is one of the main drawbacks related to the use of microwave [14; 44]. Recently, a number of microwave-assisted food processing techniques have been tested in order to overcome the limitations associated with traditional microwaving, providing the path for a promising future in process optimization [62]. Radio frequency heating is another dielectric heating technique that has drawn attention in recent years. As for microwaving, the radio frequency heating provides a fast and volumetric heating, but the difference here is that the heat is generated by friction between charged ions, which causes the entire water-containing material to be heated simultaneously [12; 19; 65]. A radio frequency treatment combined with circulating tap water was developed for quick and uniform heating of packaged whole Pacific sauries [66]. The results showed 5-log reduction of _Bacillus subtilis_ spores in the sauty with less color changes in the meat, and a softer backbone compared with conventional heating. An earlier study demonstrated that radio frequency cooking of turkey meat was four times more rapid when compared to steam cooking, while no detectable sensory differences were observed between samples [56]. Nevertheless, the use of radio frequency heating is still limited to only a few industrial applications, such as thawed frozen products [67; 68]. Ohmic heating occurs when an alternating electrical current is passed through the food, producing an internal generation of heat [2; 24; 69]. Compared with traditional heat processing, ohmic heating is advantageous with respect to cooking time. In addition, this innovative technique is environmentally friendly, efficient in terms of energy conversion, does not require heat transfer surfaces, and can reduce temperature gradients and increase cooking yield [10; 24; 70]. Although ohmic heating has shown its effectiveness in inhibiting microbial growth in many applications related to muscle foods [55; 69; 71], several aspects related to the use of this technique for manufacturing safe food need to be investigated [70]. Infrared heating involves exposure of food to infrared electromagnetic radiation (i.e., the radiation falling between the visible and microwaves ranges). Most food components absorb this kind of radiation, thus the technique is characterized by several features including uniform heating, short heating time, and energy-saving, just to mention a few [13; 19; 72]. Nevertheless, the weak penetration of infrared light limits its wider application as a heat processing method; therefore up to date, infrared heating has been used for materials of thin layer or as a supplementary heating source for muscle foods that have been already heated using ohmic heating or other heat processing techniques [19; 59; 73; 74].