凍結および解凍工程は，キンメダイをはじめとする赤色魚類の体表色の色彩変化を引き起こすことが知られているが，この色彩変化は，これらの魚の商業的価値を低下させる．本研究では，凍結解凍工程における体表色変化の原因を調べるために，キンメダイ鱗内のアスタキサンチン含量と赤色素胞の分散を測定した．凍結解凍前後の体表色をComputer Vision System を用いて数値化することにより，体表色変化は，–30 °C 下では凍結保管期間の影響を受けないことが明らかとなった．また，アスタキサンチン量は凍結解凍前後でほとんど変化しなかった．鱗内の赤色素胞の凝集と虹色素胞の損傷が，顕微鏡での観察により認められた．これらの結果より，凍結保管工程における色彩変化は，アスタキサンチンの酸化・分解だけではなく，鱗内の色素胞構造の変化にも原因があることが明らかとなった．
“Ikura,” a seasoned salmon roe product in Japan, is produced mainly from eggs of the chum salmon caught during spawning migration. Owing to the high volumes of salmon caught during peak season, appropriate storage and processing methods are essential to maintaining egg quality. We investigated the processing properties of fresh or frozen-thawed salmon eggs at different maturity levels, focusing on hardening during storage. Our results confirmed that little hardening during storage occurred in eggs in the skein state in the abdominal cavity with a low maturity level, whereas substantial hardening occurred in the individual egg grains in the peritoneal cavity. Similar results were obtained using fresh and frozen salmon eggs, and the hardening of matured salmon eggs depended on the storage time and temperature. Based on SDS-solubility and SDS-PAGE analyses, the macromolecularization of egg membrane proteins occurred during egg hardening. The frozen eggs tended to harden faster than fresh eggs, and the hardening pattern was slightly different between these eggs; these differences may be explained by various factors, such as protein polymerization and degradation. The hardening of the egg membrane progressed after salting, and this phenomenon is likely to occur during salting and aging in industrial manufacturing.
In a preliminary study to clarify the factors affecting the quality deterioration of surimi-based products, the physical properties and drip loss of five different types of commercial surimi-based products (Itatsuki-kamaboko, Chikuwa, Satsuma-age, Datemaki, and Hanpen) at different freezing conditions were evaluated. After frozen storage, the breaking strength and breaking strain of Itatsuki-kamaboko, which is a two-step-heated surimi gel without starch, decreased with frozen storage, while for the other products, which are direct-heated gels containing starch, the breaking strength and breaking strain increased. Drip loss increased after frozen storage, and the thawing drip was higher with Itatsuki-kamaboko than with other products. These changes were notable in samples subjected to slow freezing than subjected to quick freezing. Moreover, the results of physical properties and drip loss corresponded to the change in sensory characteristics. Thus, the quality change in frozen surimi-based products might be correlated to not only the freezing conditions but also the heating methods and ingredients used.
In many cases, frozen whale meat in the Japanese market is prepared before rigor mortis (pre-rigor). A serious problem for frozen whale meat is the occurrence of thaw rigor, which is the strong development of rigor mortis during thawing. To prepare frozen whale meat without thaw rigor and maintain a high meat pH, the temporal changes in adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD) contents of frozen meat stored at -2.5, -5.0, -7.5, and -10°C were investigated. The rate of decrease of ATP was higher than that of NAD at all storage temperatures. ATP nearly disappeared after holding the meat at -2.5°C for a few days; however, NAD existed yet, so pH decreased thereafter. ATP levels were maintained for a long period at a temperature of -5.0 to -10°C, resulting in the occurrence of thaw rigor. Compared to the muscles of fish such as tuna, the rates of decrease of ATP and NAD were extremely slow in whale meat.
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.