Kiyoshi Hayakawa

Improvement of a high-pressure vessel for use in a freeze pressure generation method and its application to food sterilization

A simple method for high-pressure generation and its application for microbial inactivation was studied. In order to obtain the theoretical pressure, the design of the high-pressure chamber was improved, for use on a large scale. Two types of high-pressure chambers were constructed: a pin type chamber consisting of a vessel and a cap with a pin stopper, and a screw cap type chamber consisting of a vessel and a screw cap. Pressure generated in the vessel in the temperature range from 0 to −22°C precisely fitted to the equilibrium curve of water and Type I ice. The generated pressure increased with decreasing temperature from −22 to −30°C reaching 250 MPa at −30°C. After storage of food samples in the vessels at −30°C for 24h, yeasts in nigori-zake and beer, and lactic acid bacteria in yoghurt were completely inactivated and microorganisms typically found in milk were partially inactivated.

Preparation of salt-free miso and its high pressure treatment for preservation

Abstract Pressurization completely inactivated yeast and enzymes in water but not in shiromiso . The presence of NaCl or glucose in shiromiso had an adverse influence on the high pressure inactivation of yeast and enzymes, whereas ethanol had an effective influence. For effective use of high pressure in inactivating yeast and enzymes in a foodstuff, high pressure treatment was applied to salt-free miso which was newly produced as a test product. Thus, the miso containing low salt was proved to be sterilized at a lower pressure forpreservation. These results indicate that hydrostatic pressure was available to develope new types of food which contain low salt and sugar.