Osamu Higa

Experimental Verification of the Softening of the Pork Using Underwater Shock Waves Generated by Wire Electrical Discharges

The National Institute of Technology, Okinawa College (OkNCT) has developed a food processing machine that generates underwater shock waves through wire electrical discharge. The machine can used for sterilization, milling flour, softening, and extraction among others. In this study, we experimentally examined the conditions for food softening using pork as the food material in experiments. Softness was revealed to be related to the distance of shock wave generation point from meat and the number of shockwave processing.

Numerical Simulation of Electrical Discharge Characteristics Induced by Underwater Wire Explosion

The underwater shock-wave phenomenon has been applied in various fields such as manufacturing and food processing and was investigated using many experimental and numerical analyses in the past. An underwater shock-wave is produced by various methods, e.g., underwater wire explosion and pulse-gap electrical discharge. Therefore, clarifying the shock characteristics depending on the stored electrical energy, wire dimension and material is extremely important. However, predicting the pressure and its distribution induced by underwater electrical wire explosion is hard because the phenomena associated with an elementary process are significantly complicated. In this study, to predict the discharge characteristics induced by underwater electrical wire explosion, numerical simulation based on the “simplified model of underwater electrical discharge” was performed. The numerical results show good agreement with the experimental ones.

Using Underwater Shockwaves for the Development of Processing Devices for Plant Materials

In this study, we have established a novel pretreatment system that improves the juice extraction volume and nutritional value of plant material using underwater shockwaves. The optimum treatment conditions for plant materials were obtained by conducting batch experiments using simple-structured underwater shockwave treatment equipment. From these results, a continuous underwater shockwave processing device was designed. Moreover, we have been demonstrated the applicability and reliability of underwater shockwave pretreatment in improving the yield of functional ingredients and fruit juice from plants. The instantaneous high-pressure dynamic control using underwater shockwaves is applicable to a wide range of extraction processes such as extraction of juices or ingredients from other naturally occurring foods and medicinal plants.

Underwater Shockwave Pretreatment Process to Improve the Scent of Extracted Citrus junos Tanaka (Yuzu) Juice

Citrus junos Tanaka (yuzu) has a strong characteristic aroma and thus its juice is used in various Japanese foods. Herein, we evaluate the volatile compounds in yuzu juice to investigate whether underwater shockwave pretreatment affects its scent. A shockwave pretreatment at increased discharge and energy of 3.5u2009kV and 4.9u2009kJ, respectively, increased the content of aroma-active compounds. Moreover, the underwater shockwave pretreatment afforded an approximate tenfold increase in the scent intensity of yuzu juice cultivated in Rikuzentakata. The proposed treatment method exhibited reliable and good performance for the extraction of volatile and aroma-active compounds from the yuzu fruit. The broad applicability and high reliability of this technique for improving the scent of yuzu fruit juice were demonstrated, confirming its potential for application to a wide range of food extraction processes.

Effects of improving current characteristics of spark discharge on underwater shock waves

We have been developing a food-processing device that uses underwater shock waves generated by spark discharges at an underwater spark gap. Underwater shock waves can be used in food processing for softening, fracturing and sterilization. These technologies are attracting attention because the food is not heated during processing, so it does not change flavour. In this study, we develop a rice-powder manufacturing system using the fracturing effect provided by underwater shock waves. Because rice grains are very hard, the process must be applied repeatedly using a momentary high pressure to fracture the grains. The fast repeated generation of shock waves should provide high pressures from low energies. Therefore, we aim to achieve higher pressures from low energies expended by the underwater gap discharge. We increase the pulse compression rate by decreasing the circuit impedance of the device and increasing the charging voltage. Using optical observations and a pressure sensor, we measure the high pressure developed by the underwater shock wave and the rise time of the discharge current. We find that we can decrease the rise time of the discharge current by 17% while maintaining the peak current, and simultaneously increase the high pressure of the underwater shock wave by 135%.