室温磁気冷凍技術は高効率な次世代ノンフロン型空調冷凍技術として注目されているが，一部の用途を除き実用に耐えうる冷凍能力の実現には至っていない．本研究では磁気冷凍機の冷凍能力向上を目指し，Active Magnetic Regenerator に則った冷凍サイクルの改良に着目した．数値計算から得られる冷凍能力を目的変数とし，山登り法を用いて室温磁気冷凍機における最適な冷凍サイクルを，冷凍温度幅とAMR 寸法が異なる複数の場合について探索した．その結果，磁気冷凍機で一般的に用いられることが多いブレイトンサイクルとエリクソンサイクルを複合した冷凍サイクルを用いた場合に高い冷凍能力が得られることがわかった．
The effect of pre-treatment at subzero temperature of grains on the grinding process was investigated in respect of physical properties of particle. The average particle size of ground soybean and black soybean powders decreased as pre-treatment temperature decreased. The theoretical model that described grinding characteristics revealed that the freezing as pre-treatment is effective on grinding process. In all grain samples, the Bond’s constant and work index showed lower values as the pretreatment temperature decreased. The scanning electron microscopy was used for observation of surface damages on the particles by grinding process. Some cracks were seen on the surface of particles of soybean powder ground with freezing pretreatment. On the other hand, the particles of black soybean powder showed no fractures. The freezing as pre-treatment of grains prior to grinding process is effective to controlling their grinding characteristics and microstructure damages.
Nowadays, fluorescence spectroscopy has been used as a potential method for nondestructive quality measurement of food materials. Fluorescence fingerprint (FF) of adenosine 5’-triphosphate (ATP) has been observed during the quality assessment of different raw food materials. Although the fluorescence spectra of ATP can be affected by various factors including pH, the details are not clarified yet. Thus, the study attempts to demonstrate the effects of pH (5.0-8.0) on the FF data of ATP standard solutions (10, 5 and 1 µmol/mL for both frozen and non-frozen states). The results of the present study revealed that the strength of the fluorescence signal was influenced by not only the concentration of ATP but also by the pH of samples. The highest fluorescence intensities were observed from the non-frozen ATP solutions at pH 5.0 for each concentration which declined drastically with increasing pH. The majority of frozen ATP samples showed the similar trends of wavelength conditions to get highest fluorescence intensity. Small pH changes affected the intensity and spectral characteristics of FF and it even shifted the peak wavelength conditions. The implementation of this method would be a help to ensure the validity of FF and optimize it as a technique that can be used to verify the effects of pH on many constituents of food.
The effect of freezing, and iced and hot water thawing on the quality of durian pulp was investigated. Mature durian pulp was removed with seeds, vacuum-packed, and frozen at -20°C. Thawing in iced water (~0°C) and hot water (~90°C) was then applied and the quality of the pulp was assessed based on physicochemical properties (pH, moisture content, soluble solids concentration (SSC), color, sugar content (sucrose, glucose, and fructose), and organic acid content (succinic acid and citric acid ), texture and smell profile. Overall, the freezing and thawing conditions, particularly the hot water thawing, posed an effect to the moisture content, color, and smell profile of the durian pulp. A significant increase in the moisture content, as well as a decrease in the color brightness was observed. Furthermore, the hot water-thawing process also induced slight variation to the smell attribute and strength of the entirety of smell. Although the sugar content significantly decreased after freezing and thawing, it was only affected by the freezing process but not by the thawing conditions. No significant variations were noted in the pH, SSC, organic acids and texture of the frozen durian pulp.
Effects of freezing storage and high hydrostatic pressure on microbial (Escherichia coli) viability in liquid whole egg (LWE)-sucrose mixture were investigated. Liquid whole egg with different sucrose concentration (0, 20 or 50 wt%) was pressurized at 400 MPa and then frozen at -20°C for a week. The viable cell count was estimated by monitoring the changes in absorbance values during cultivation at 660 nm with 30-min interval. Survival curves obeyed the first-order inactivation kinetics. The viable cell counts in frozen-thawed LWE-sucrose mixture was lesser than those of unfrozen samples. Effect of sucrose content on high-pressure-mediated inactivation varied at 20 wt%. Thermal analysis of LWE-sucrose mixture showed that the thermal denaturation enthalpy of LWE-sucrose content of 20 wt% was highest in all tested conditions, which also showed protective effect against thermal denaturation. LWE-sucrose (20 wt%) mixture has protective effects on pressure inactivation of E. coli, while LWE-sucrose (50 wt%) showed inactivation effect based on the strong dehydration ability on E.coli and LWE mixture by osmotic pressure.
Effects of immersion in agro-products (kiwifruit, Japanese radish, Maitake mushroom and pineapple) homogenates and freezing on the qualities of raw octopus were investigated. Octopus muscle fibers observed under TEM were significantly destroyed after freezing at -20°C. Immersion of octopus in homogenates also destroyed octopus muscle fibers. The initial modulus of the octopus samples, as measured with creep meter, decreased significantly after immersion in homogenates of agro-products and freezing. However, the individual initial modulus of the samples did not show significant difference among each other. Taurine and glutamic acid concentrations were measured by HPLC and dabsylation method. The estimated taurine concentrations of the samples in all tested octopus were similar, while the glutamic acid concentrations in selected samples increased after the application of the immersion in agro-product homogenates and freeze-thawing treatment.