# Novel Techniques for Microbiological Safety in Meat and Fish Industries
## 6 Non-Thermal Preservation Techniques
### High Pressure Processing  
Until now, the most successful alternative non-thermal technology in the food industry was High-Pressure Processing (HPP) [95]. Food products represent an important market share for the use of HPP in the food industry, with meat products representing 25 to 30 percent of the total foods processed under high pressure (HP). Therefore, over the period between 2013 and 2016, the number of HPP units in industrial operations doubled from 215 to 430 HPP units [96]. HPP is used in several other finished meat products as an efficient way to inactivate and monitor pathogenic bacteria such as _Listeria_, _Salmonella_, and _E. coli_, avoiding food-borne contamination and outbreaks. HPP has numerous advantages to ensure food safety and has significant and unique value for the industry. HPP can impact the labile nature of proteins, especially in fresh meats, when used under certain processing conditions, such as temperature [T], pressure [P], and time [t]. HPP has moderate to serious negative impacts on the meat appearance and other quality features depending on the applicable conditions, which is why wide implementation of HPP technology in the meat industry is very limited [95]. High-pressure processing requires pressures of at least 100 MPa, with the most common range being 100-1000 MPa, and can work in temperatures ranging from \(-20\)\({}^{\circ}\)C to 90 \({}^{\circ}\)C. At certain temperatures for appropriate time and pressure levels, non-covalent bonds, such as hydrogen bonds, ionic bonds, and hydrophobic bonds, are destroyed. Enzymes, proteins, starch and other molecular biological substances are deactivated, denatured and gelatinized, respectively, and microbes will be killed for the sake of food safety and preservation [97]. During the HPP process, the pH of meat will decrease, and pressure level, treatment time and temperature, muscle type, and meat temperature are some main factors which effect the high level of pH in meat. After being subjected to high pressure, the fresh meat witnessed a rapid fall in pH and an intense contraction. The red meat pH decreased by 0.6-0.8 units after 100-150 MPa pressure for 1-5 min at 35 \({}^{\circ}\)C. However, the pH of white meat reduced more significantly after 10 min of pressurization [97]. It is observed that the WHC of yak meat is increased and then decreased with an increase in pressure and processing time. A total of 10.50% WHC increased, and meat color changed into white at 250 MPa pressure for 15 min [98]. Myoglobin is the largest meat pigment and accounts for 90-95% of the total pigment content of meat, chemical-physical and concentration state of myoglobin in fresh and processed meat have a major step in color. Color changes in meat in HPP depends primarily on three primary factors: (1) denaturation of myoglobin, (2) modification or disruption of the porphyrin ring, and (3) changes in the myoglobin redox chemistry. At pressures below 300 MPa and low temperatures, HPP creates slight color changes then high pressure; however, the denaturation of myoglobin occurs at a low pressure due to its instability. High-pressure treatment could alter muscle microstructure, sarcomere contraction, muscle fiber damage, and myofibril fragmentation by hydrolyzing muscle fiber proteins, weakening cell structure, releasing ions, and activating calcium-activating enzymes [97]. When compared to traditional thermal processing, HPP has the following advantages: shorter processing times; minimal heat penetration/heat damage issues; excellent freshness, flavor, and color retention; no vitamin C loss; and minimal functionality changes, avoiding chemical additives or high temperatures in order to meet consumer demand without causing consumer dissatisfaction. Microorganisms and enzymes can be inactivated at low temperatures, while highly valued low molecular constituents such as bioactive components, vitamins, colors, and flavorings are largely unaffected [99].