Recently significant progress has been made in research into applications of the high-pressure treatment method. This is because it has been demonstrated that high-pressure treatment can induce additional new phenomena when used in combination with other physical, chemical or biological treatments. Practical results can be obtained when two or more phenomena induced by high-pressure treatment are combined, for example, acceleration of enzyme reactions, acceleration of reactions by the breakdown of cell walls, penetration of water into the inside of rice grains, elimination of air bubbles in a wide range of grains, and sterilization obtainable by the synergic action of high-pressure and pulsed electric field application. These extended techniques are expected to form the main stream in the research of practical applications in the future. Therefore, the idea has emerged to call such application techniques “Hi-Pit” (High-Pressure Induced Transformation).
This paper describes general methods to eliminate or decrease the allergenicity of food protein, and also describes high pressure-induced elimination of the allergenicity of food protein, especially meat protein.The effect of high pressure treatment on the elimination of bovine serum albumin (BSA, the major beef allergen) allergenicity was evaluated on the basis of histamine release from human basophilic KU812F cells sensitized with sera from allergic patients, and the structural changes of BSA responsible for reducing allergenicity was estimated. BSA pressurized at pressures ranging from 300 to 600 MPa reduced histamine release from the cells sensitized with A5 serum with significance. The reducing effect of high-pressure treatment gradually increased with the increase of pressure applied to BSA. The pressure-induced structural changes of BSA were estimated by fluorescence spectra, circular dichroism (CD) spectra (the content of secondary structure), the amount of surface sulfhydryl (SH) group, and the surface aromatic hydrophobicity. The blue shift and decrease of the fluorescence of BSA gradually progressed with the increase of pressure applied. But no significant effect of pressure on CD spectra was observed. Pressure-treated BSA showed the maximum increase in the amount of SH group by pressure treatment at 100 MPa, and the aromatic hydrophobicity gradually decreased with the increase of high pressure applied. These results indicated that high pressure treatment induced the tertiary structural changes of BSA, but no effect on the secondary structure. We concluded that the pressure-induced elimination of BSA allergenicity seemed to be related to the tertiary structural change of BSA.
In the last decade, there has been increasing interest in developing high pressure-processed foods in Japan and the world, because apparatus for high hydrostatic pressure treatment has become commercially available. Meanwhile, efforts are also being made to demonstrate the potential benefits of high pressure processing for the preservation and modification of foods including meat and meat products. In this article, we introduce recent data concerning the specific effects of high pressure on meat and meat products. The present situation and future view of high pressure technology for meat industry are also described.
This study concerns the rheological properties and microstructure of pressure-induced gels (800 MPa, 30°C, 10 min) from the mixture of whey protein isolate (WPI) and mucopolysaccharide (10% or 20% chitosan (CN), 0.25% or 0.5% hyaluronic acid (HA) or 3∼10% chondroitin sulfate (ChS) were added in 20% w/v WPI). CN increased the hardness and breaking stress of gel and restrained the phase separation during gelation under high pressure. HA decreased the hardness and breaking stress of gel, and converted the microstructure to a coarser structure formed with micro-particles. ChS did not affect the rheological properties of gel, but such gel has similar effect to the microstructure of gel with HA. The results suggest that coacervation in the presence of an anionic polysaccharide is triggered by whey proteins gelation under high pressure.
Effect of high pressure on starch, a major food component, is reviewed. When heated with sufficient water, starch granules absorb water and swell. This is termed heat gelatinization. Starch can be gelatinized by high pressure. Compared with heat gelatinization, “pressure gelatinization” is less clarified due to much shorter history of the research. Nevertheless, reports on the pressure gelatinization of different starches under various conditions (pressure, temperature, and water content) may give us insight into pressure gelatinization, which has been analyzed by X-ray diffractometry, differential scanning calorimetry, light microscopy, Fourier transformed infra-red spectoscopy, nuclear magnetic resonance and so forth. Although a systematic understanding of pressure gelatinization is still incomplete, some characteristic features of pressure gelatinization have been already clarified.
High pressure research system using the synchrotron radiation and the Kawai-type of high pressure apparatus was installed at BL04B1 beamline of SPring-8 in 1997. The BL04B1, named “High Pressure and High Temperature” beamline has been designed to conduct research on the structure and properties of materials under high pressure and high temperature. The developments of the beamline and experimental facilities during the eight years are summarized. In addition, recent researches using the newly developed techniques are also reviewed.
The effect of the combination of hydrostatic high-pressure (HHP) and pulsed electric field (PEF) treatments on the inactivation of Bacillus subtilis spores was investigated, using suspensions prepared by suspending the spores in various solutions at about 108 spores/ml. When the PEF and HHP treatments were successively conducted in that order, the results were compared with the case where either was conducted alone. The combined processing achieved a 7.1 log reduction in the viable spore counts at maximum. Low-temperature storage after the combined processing further led to reduced germination, and finally completes inactivation in 3 days. It was confirmed by phase-contrast microscopy that the non-treated spores gradually turned into phase-dark spores and finally germinated and changed into vegetative cells, while the spores subjected to PEF/HHP treatment did not transfer to the phase-dark stage, meaning no germination.