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.
The process of freezing and thawing causes the discoloration in the body surface of red-colored marine fishes such as alfonsino; which lowers their commercial values. The astaxanthin content and dispersion of erythrophore in the scale of alfonsino were measured to investigate the causes of the discoloration during freezing and thawing. Color measurement of the surface of alfonsino using the computer vision system showed that the discoloration during freezing and thawing was not affected by the storage period at –30 °C. In addition, there was little change in the astaxanthin content in the scale of alfonsino before and after freezing and thawing. The aggregation of erythrophores and damages to iridophores by freezing and thawing were confirimed by microscopic observations. These results demonstrated that the discoloration in alfonsino during freezing and thawing was caused not only by the oxidization and degradation of astaxantin, but also by the structural changes of the chromatophore in the scale.
“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.
Mackerel is weak against freezing, therefore a high quality freezing method that prevents deterioration is essential. We investigated the effects of freezing condition (freezing atmospheric temperatures at －20, －40, － 80oC and －196 oC) and lipid content on ice crystal size, K value, drip loss and pH in frozen mackerel. Lipid contents of mackerel effected on the K values, drip loss, and ice crystal sizes in frozen mackerel. Therefore, selected freezing conditions for different lipid content in mackerel would lead to regulate quality parameters such as K value, drip loss and ice crystal size.
We investigated the effects of storage conditions on the quality parameters (texture, softness and juiciness) of fried chicken products. Texture profile analyses showed the storage condition (25 oC 40%RH) to maintain the quality of fried chicken products comparing with immediately after frying. On the other hand, samples stored at higher temperature or higher humidity resulted in acceleration of deliquoring and hardening. Fried chicken products stored at 40oC and40%RH could maintain the weight, texture and juiciness during storage.
In recent years, greenhouse gas control and energy saving have been required to prevent global warming. In residential air conditioners, switching to R 32, for which the GWP is as low as 1/3 of R 410A and superior in terms of safety and economy, is being pursued. Several new HFO-based mixed refrigerants have also been proposed which is excellent in terms of low GWP. Therefore, we have compared the performance among R 32 and newly proposed HFO-based mixed refrigerants by drop-in test and system simulation for VRF systems in commercial buildings since swiching to low GWP will be required in the future.
A novel heat exchanger using parallel small refrigerant channels has recently been developed for high performance air conditioning systems. However, due to non-uniformly heat load among channels, boiling flow tends to be unevenly distributed in parallel channels. This phenomena makes accurate prediction of heat transfer capacity difficult. In this study, experiments on flow boiling in non-uniformly heated two parallel mini-channels were carried out, and averaged heat transfer coefficients in two channels were investigated. When non-uniformly heat load was applied, dryout occurred in relatively wide range in a higher heated channel. As a result, the averaged heat transfer coefficients in non-uniformly heated channels tended to reduce compared with those under the uniform heat flux conditions of the same averaged heat fluxes.
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.
One of the main concerns regarding in-vessel retention (IVR) during a severe accident is guaranteeing sufficient cooling performance to avoid the melt-through of the pressure vessel. In such an event, the vessel is submerged in water, and boiling is occurred to remove the heat. However, the main problem is that there is a limit to the pool boiling heat transfer at the outer surface of the reactor vessel due to occurrence of critical heat flux (CHF) conditions. Therefore, CHF enhancement is important to increase safety margin of IVR. In previous studies, CHF was enhanced approximately twice compared to bare surface by attaching honeycomb porous plate (HPP) to the heated surface. In order to establish the IVR, the cooling technology should be considered in forced flow boiling with the downward heat transfer surface. Moreover, we proposed a two-layer structured HPP for further CHF enhancement. Therefore, in the present paper the effect of the single and two layers HPPs on the critical heat flux under flow boiling with the downward heat transfer surface was investigated experimentally. As a result, the coalescent vapor bubbles cover the heated surface for a long period depending on the flow pattern under the flow boiling condition, resulting in liquid drying inside a HPP and reduction of CHF. Even in this situation, a two-layer structured HPP can be applied to CHF enhancement in flow boiling with the downward heat transfer surface.
Interest in the room temperature magnetic refrigerator, which is an environmentally friendly refrigeration system, is increasing. Previous studies have revealed that the maximum temperature span of the magnetic refrigerator is expanded by layered beds of multiple materials with different curie temperatures in AMR(Active Magnetic Regenerator). But, the effective factors of the layered beds configuration of multiple materials are not revealed. In this study, we investigated with one dimensional heat transfer numerical analysis the performance of layered beds of manganese(Mn) based compounds which has a larger magnetic entropy change than conventional gadolinium(Gd) based compounds. Analysis results show that when the AMR duct length and the curie temperature of the cold end and hot end materials are fixed, the achieved temperature span of multi layered beds is not affected by the curie temperature interval, while its cooling power is increased with the decreasing of the curie temperature interval. In the layered beds of multiple materials with the preferable curie temperature interval, the achieved cooling power is determined by the cold side materials, on the other hand the temperature span is expanded by the other materials.
In selecting a refrigerant, it is necessary to consider not only ODP and GWP but also the impact on global warming from various aspects. It is therefore indispensable to continue to search for better refrigerants that minimize impact on the climate to the total CO2 equivalent. Recently, a new refrigerant R 452B was reported as a high-efficiency refrigerant. There is a possibility that excellent performance may be exhibited depending on the use load of the air conditioner. We carried out cooling performance comparison in wide capacity range for R 452B and R 32. As a result, it was found that the performance difference becomes large in high ambient temperature and high heat load. We also analyzed the causes.
Frost formation in heat exchangers is an important problem because frost lowers energy efficiencies of refrigeration and air conditioning systems. In this study, we investigated frost formation on a flat plate under forced convection with air temperatures of -45 to -5 ℃. After frost growth for 3 to 130 min, the cooling surface was heated stepwise below the melting point of frost and the occurrence of a separation phenomenon between the frost layer and the cooling surface was verified. It is conjectured that sublimation of the frost layer was caused by the heated plate and then mass transferred to the upper part of the frost which is cooled by low temperature air. This phenomenon is thought to reduce adhesion of frost, thereby causing separation. This paper introduces the separation phenomenon and the boundary conditions under which it occurs. It is expected that this phenomenon will become an effective defrost method for air coolers in cold storage rooms.
Herein, the distribution characteristics of a vertical header exceeding 30 branches were experimentally clarified. In our experiments, the flow rate and the quality were changed in a plurality of shapes and refrigerant state. Our experimental findings indicated that the liquid refrigerant maldistribution downward to the lower part, the non-reachable part to the upper part, the drift to the upper part, the flow almost uniformly. Additionally, it was clarified that the quality does not reach the upper part of the header depending on the conditions, and flow may become be maldistribution. Furthermore, the header diameter corresponding to the flow rate and the quality of the refrigerant can be estimated by creating a relational expression between the reaching height ratio H of the liquid refrigerant and the Wallis dimensionless number C.
Metal 3D printing(additive manufacturing) has shown promise as a method of fabricating high-performance heat sinks, owing to its ability to produce optimized structures of any design. In this study, computational fluid dynamics was initially performed to investigate the heat transfer performance of heat sinks with lattice structures. The heat sinks were then fabricated using 3D printing, and their actual heat transfer performance was compared with the findings from the numerical computational fluid dynamics. Additionally, X-ray CT scanning was used to measure the three-dimensional shape and surface area of the fabricated objects, and computational fluid dynamics accounting for inherent surface roughness of 3D printed objects was performed on the 3D shapes derived from these measurements. This analysis revealed that lattice structural heat sinks have a more effective heat transfer coefficient than finned heat sinks. Further, while the surface area of the fabricated structures was greater than the design values owing to the roughness in the surface profile, it was evident that this surface roughness degraded the heat transfer performance.
An Active Magnetic Regenerator (AMR) cycle that employs magnetocaloric materials (MCMs) as regenerators is generally used to realize the effective temperature span for magnetocaloric heat pump systems. The MCMs of the first-order phase transition materials have gained attention because of the latent heat involved in their phase transitions. However, because the range within which the MCM exhibits an magnetocaloric effect (MCE) is narrow near its Curie temperature, only a narrow temperature span exists in the case of the AMR with a single MCM. Therefore, there is a demand for the AMR system with material layers made of a couple of MCMs. However, only few studies have investigated the influence of the properties of MCMs on magnetocaloric heat pumps using material-layered systems. In the present study, the refrigeration capacity and the temperature span of the magnetocaloric heat pump with a material-layered bed of manganese-based compounds, which are first-order phase transition materials, were determined. It was found that the temperature span can be extended by optimizing the volumetric flow rate and the number of the layers that constitute the AMR. In addition, the number of the layers and the refrigeration capacity were found to be related.