Static high-pressure processing

The use of emerging food technologies such as ultrasound, static high-pressure processing and microfluidisation may provide the platform for the creation of novel micro structured assemblies to meet future needs and provide new processing or preprocessing capabilities for encapsulation systems. 

Processes without catalysts are only of minor industrial importance, since they provide only gray graphite-contaminated diamond powder with a maximum crystal size of ca, 50 Xm and require significantly higher pressures of 120 to 300 kbar. In the dynamic process operated by DuPont the pressure and temperature are produced for a few microseconds in a shock wave apparatus. The starting material is also graphite, which should be as crystalline as possible. Static high pressure synthesis processes without catalysts are industrially unimportant. 

The addition of mineral salts to alter protein and mineral equilibria in milk is a strategy that has been used to manipulate milk functionality, either alone or in combination with other processing treatments, such as alteration of pH, ultrafiltration, diafiltration, heating and cooling, or static high-pressure treatment. 

High-pressure processing normally involves immersion of packaged meat in a liquid-filled chamber and can be either static with a steady increase in pressure or dynamic with a sudden increase in pressure such as from a shock wave. For additional information on the effects of high-pressure processing on the quality of various foods, including animal products, the reader is referred to Chapter 5. 

In this process, diamond forms from graphite without a catalyst. The refractory nature of carbon demands a fairly high temperature (2500—3000 K) for sufficient atomic mobiUty for the transformation, and the high temperature in turn demands a high pressure (above 12 GPa 120 kbar) for diamond stabihty. The combination of high temperature and pressure may be achieved statically or dynamically. During the course of experimentation on this process a new form of diamond with a hexagonal (wurtzitic) stmcture was discovered (25). 

It has been a persistent characteristic of shock-compression science that the first-order picture of the processes yields readily to solution whereas second-order descriptions fail to confirm material models. For example, the high-pressure, pressure-volume relations and equation-of-state data yield pressure values close to that expected at a given volume compression. Mechanical yielding behavior is observed to follow behaviors that can be modeled on concepts developed to describe solids under less severe loadings. Phase transformations are observed to occur at pressures reasonably close to those obtained in static compression. 

The components of an ELM system are the diluent, surfactant, internal aqueous phase, continuous phase, and carrier in the case of type 2 facilitation. Emulsification is usually achieved by high speed or ultrasonic stirrers for batch operations and high-pressure static dispersion or colloid mills for continuous mode [46]. The presence of a surfactant is necessary to ensure adequate stability of the emulsion during the extraction process. However, an ultra stable emulsion is not desirable as it will lead to difficulties in the demulsification stage. Eor the effective working of an ELM all components must be carefully chosen and each composition is critical. Some of the desirable properties of the various components are listed in the following sections. 

In many cases, the extraction process includes an additional, static extraction step. To this end, the outlet valve (OV in Fig. 6.10) is supplemented by an inlet valve (IV in Fig. 6.10) between the high-pressure pump and the extractor. Once the system has been pressurized, the inlet valve is closed, the high-pressure pump stopped and the oven temperature raised. After the desired temperature is reached, the system is maintained under a static regime with both valves closed, and then the valves are opened and the pump restarted to allow the solvent to flow over the dynamic extraction period. Several studies [147,150,153] have shown that a combination of both extraction modes can result in substantially improved extraction and shorter extraction times. This is commented on in greater detail in discussing specific applications below. 

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