The effect of the freezing process and frozen storage periods on the microstructure of cooked glutinous rice has been investigated. Cooked glutinous rice (cv. Koganemochi) was frozen and stored in a household freezer (about -22 °C) during 1, 5, 10, 30 and 60-day storage periods. Its microstructure was observed by using fluorescence staining method and the morphology of ice crystals including equivalent diameter and number was analyzed. Colorimetric measurements were conducted after natural and steaming thawing on samples of each storage period. It was found that average equivalent diameter and number of ice crystals increased with storage period from 5 days, and recrystallization occurred in temperature fluctuation during freezing process and storage affected microstructure of glutinous rice. Moreover, by analyzing the distribution of ice crystals, it was found that most of them are under 10µm in each storage period. Frozen stored glutinous rice after 60 days showed darker and more unpleasant color than freshly cooked one by both thawing methods. Since the tendency of color change during the whole frozen storage was unstable, it could be assumed that the control of thawing process should not be neglected.
The effects of the freezing process and frozen storage periods on rheological parameters of freshly cooked and freeze-thawed glutinous rice have been investigated. Cooked glutinous rice (cv. Koganemochi) was frozen and stored in a household freezer at -20°C for 1, 5, 10, 30 and 60 days. After steaming and natural thawing processes, creep-recovery test (0.1N, small deformation), texture profile analysis (TPA) test (50% deformation) and the tensile testing (20N, 100% deformation) were performed on one-grain and block-shaped glutinous rice respectively by a rheometer, to measure the rheological parameters of the samples. One-grain samples showed more significant differences with freshly cooked rice in tensile testing, while blockshaped ones showed more in creep recovery tests. There were few significant differences in any fracture characteristics and viscoelastic properties between steaming and natural thawing methods for both block-shaped and one-grain samples in each storage period. The TPA results demonstrated that natural thawing method would produce softer as well as less sticky glutinous rice products during 60-day frozen storage.
Pizza dough samples were frozen and stored at different temperature (-5̊C, -15̊C, -25̊C, -35̊C and -45̊C) and for different storage periods (1 day, 15 days, 25 days and 35 days) to measure the baking characteristics of the samples in a hot air (HA) and superheated steam (SHS) oven. Baked samples were employed for the measurement of surface color and moisture content. The moisture content of the samples frozen at -5̊C significantly decreased after 15 days of frozen storage. The surface color of the SHS-dried samples changed more drastically than that of HA-dried samples. Compared with HA, the SHS baking showed the potential to give the frozen pizza dough higher thawing rate, less baking time, and faster browning ability. The combined effect of initial condensation, crust thickness and water redistribution from crumbs to crusts might have played important roles in differentiating the HA- and SHS-baked samples. Different freezing temperatures from -5 ℃ to -45 ℃ did not cause any significant difference in color.
Five Philippine durian cultivars - Puyat, Duyaya, GD69, Native, Arancillo, were subjected to consumer intensity-ranking test with 50 durian consumers as panelists to determine the correlation between the experimental measured values and the consumers' perceived intensity of the different durian quality attributes: color, texture, physicochemical properties, sugars, and organic acids content. Preference ranking test was also performed to identify the most preferred cultivar based on the five quality attributes evaluated. Results of the intensity ranking showed a good correlation between the experimental values and sensory perception on the color, texture, sweetness and overall flavor. Same trends in the degree of intensity were observed in the measurements, objective and sensory analysis. In the preference-ranking test, results revealed that Duyaya was the most preferred cultivars in terms of the color, while Arancillo was rated most preferred for the texture. In reference to the taste/flavor, the top choices were Arancillo, Duyaya, and Native. On the other hand, Puyat, GD69, and Arancillo registered the highest consumer preference in regard to aroma, although the mean rank of the former did not seem to differ with the two former cultivars. Finally, upon consideration of the overall preference, our findings suggested that Duyaya, Arancillo, and Native were more favored cultivars over Puyat and GD69.
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.