High hydrostatic pressure applications

High hydrostatic pressure (HHP) and pulsed electric fields (PEFs) are rather novel technologies where relatively little research has been carried out. These methods have mostly been tested in combination with other decontamination methods and also mostly on either microorganisms in vitro or on foods of animal origin (e.g. milk, eggs and meat) (Raso and Barbosa-Canovas, 2003 Ross et al., 2003). More research is needed in order to find out if such methods are applicable to the fresh produce industry. 

With the technical development achieved in the last 30 years, pressure has become a common variable in several chemical and biochemical laboratories. In addition to temperature, concentration, pH, solvent, ionic strength, etc., it helps provide a better understanding of structures and reactions in chemical, biochemical, catalytic-mechanistic studies and industrial applications. Two of the first industrial examples of the effect of pressure on reactions are the Haber process for the synthesis of ammonia and the conversion of carbon to diamond. The production of NH3 and synthetic diamonds illustrate completely different fields of use of high pressures the first application concerns reactions involving pressurized gases and the second deals with the effect of very high hydrostatic pressure on chemical reactions. High pressure analytical techniques have been developed for the majority of the physicochemical methods (spectroscopies e. g. NMR, IR, UV-visible and electrochemistry, flow methods, etc.). 

In high-pressure applications these are two main trends of research high hydrostatic pressure treatment (2000-7000 bar) and supercritical CO2 treatment. In both cases the aim is to inactivate the micro-organisms in order to protect and preserve foods, and so to prolong their shelf-life. 

The low water absorptivity and good resistance to hydrostatic pressure make syntactic foams very useful for marine and submarine construction. Materials to be used for deep-sea application must have 1) low compressibilities at high hydrostatic pressure, 2) low thermal expansion coefficients, 3) low water absorption, and 4) good fire resistance. The fluids used for buoyancy in deep water submersibles include gasoline, ammonia, and silicone oil, while the solids include plastic, glass and aluminium foams, lithium, wood, and monolithic polyolefins. The liquids are dense but have low... 

McDonough and Hemmingsen (ref. 419) confirm that for bubbles to develop in vertebrates from such low gas supersaturations, some mechanism or structure must promote the initial in vivo bubble nucleations. They cite, as one initial possibility, the popular, general hypothesis that animals contain a reservoir of microscopic gaseous nuclei in the body fluids or tissues, which expand into bubbles when the organism is decompressed (ref. 2). These authors point out that results consistent with this hypothesis have been obtained with shrimp (ref. 429) and rats (ref. 430), where the application of relatively high hydrostatic pressure before decompression apparently reduced the incidence of bubble formation, presumably by forcing potential gas nuclei into solution before they could serve as bubble precursors (ref. 419). 

The types of hollow fiber membranes in production are illustrated in Figure 3.32. Fibers of 50- to 200-p.m diameter are usually called hollow fine fibers. Such fibers can withstand very high hydrostatic pressures applied from the outside, so they are used in reverse osmosis or high-pressure gas separation applications in which the applied pressure can be 1000 psig or more. The feed fluid is applied to the outside (shell side) of the fibers, and the permeate is removed down the fiber bore. When the fiber diameter is greater than 200-500 xm, the feed fluid is commonly applied to the inside bore of the fiber, and the permeate is removed from the outer shell. This technique is used for low-pressure gas separations and for applications such as hemodialysis or ultrafiltration. Fibers with a diameter greater than 500 xm are called capillary fibers. 

Mozhaev, V., Heremans, K. Frank, J., Masson, P., Balny, C., 1994, Exploiting the effects of high hydrostatic pressure in biotechnological applications, Tibtech. 12 493-501... 

Ashie, I.N.A. and Simpson, B.K. Application of high hydrostatic pressure to control enzyme related fresh seafood texture deterioration. Food Res. Int., 29, 569, 1996. 

Palou, E., Lopez-Malo, A., Barbosa-Canovas, G.V., and Welti-Chanes, J. High hydrostatic pressure and minimal processing. Minimally Processed Fruits and Vegetables. Fundamentals and Applications, S.M. Alzamora, M.S. Tapia and A. Lopez-Malo, eds.. Aspen, Maryland, 2000. 

Trujillo, A. J., Capellas, M., Saldo, J., Gervilla, R., and Gnamis, B. 2002. Applications of high hydrostatic pressure on miUc and dairy products A review. Innovative Food Science and Emerging Technologies 3 295-307. 

Neetoo, H., Ye, M., and Chen, H. 2008. Potential application of high hydrostatic pressure to eliminate Escherichia coli 0157 H7 on alfalfa sprouted seeds. International Journal of Food Microbiology 128 348-353. 

Suzuki, A., K. Kim, H. Tanji, T. Nishiumi, and Y. Ikeuchi. 2006. Application of high hydrostatic pressure to meat and meat processing. In Advanced Technologies for Meat Processing,... 

Apart from hot extrusion, VjSi can be deformed plastically at room temperature in spite of its brittleness by superimposing a high hydrostatic pressure which makes the production of multifilament, superconducting wires feasible for applications in solenoid magnets (Wright, 1977). Laminar VjSi can be prepared by solid-state, thin film reactions between V and SiOj on Si substrates (Hayashi etal.,... 

Bayindirli et al (2006) studied the effectiveness of treatment on pectinesterase activity in orange juice, comparing the application of high hydrostatic pressure with a mild heat treatment. The residual pectinesterase activity in the orange juice after treatment at 450 MPa and 50°C for 30 minutes was determined as approximately 7 1.6%. This compares with 12 0.2% after a treatment of 40°C and 450 MPa for 60 minutes. The inactivation was irreversible and the enzyme was not reactivated when stored at 4 and 25 °C for 1 week. 

Mozhaev, V. V., Lange., R., Kudr3 shova., E. V., and Balny, C. (1996). Application of high hydrostatic pressure for increasing activity and stability of enzymes, Biotechnoi. Bioena.. 52(2), 320-331. 

It is possible to produce orientation at normal temperatures in a brittle thermoplastic like polystyrene, by the application of a sufficiently high hydrostatic pressure during extension. The hydrostatic pressure prevents brittle failure at small strains, and can be regarded as reducing Ty, below ambient temperature. Similar results may be obtained by hydrostatic extrusion, where a billet of the polymer is forced through a reducing die under the pressure of a hydraulic fluid. An example of the properties achieved in this way has been given in Section 1.2 above. 

Ashie, I.N.A. Application of high hydrostatic pressure and oc2-macroglobulin to control postharvest seafood texture deterioration. Ph.D. thesis, McGill Univ., Montreal Canada, 1995, 239 pp. 

There are in fact some bromine applications that are not questioned from an environmental point of view. Bromine has a similar usage to chlorine for water disinfection. Silver bromide is used as a Hght-sensitive substance in photographic emulsions. A quarter of aU bromine used finds its way down into boreholes in oilfields, where calcium and zinc bromide solutions are used as drilling fluids. In high concentrations, the liquids are heavy and exert a high hydrostatic pressure that prevents the very disturbing blow-out situations. 

The application of high hydrostatic pressures has a pronounced effect on the electron mobility. While in neohexane (2,2 DMB), increases from the value at 1 bar to 3 kbar by 30% in TMSi and n-hexane Pgi decreases with increasing pressure. The results of measurements are shown in Figure 9. 

Raman spectra of single-walled and multiwalled nanotubes under high hydrostatic pressures were published by Thomsen et al. [101]. Not surprisingly, the band frequencies increased with increased pressure. In an article published simultaneously with the one just cited, Thomsen et al. [102] lamented the difficulty of purifying nanotubes for technical applications. Chemical methods are inexpensive, but they alter the structures. Chromatography works well, but the yields are poor. 

---