Frozen fish meat incurs thaw rigor if frozen immediately after sacrifice. In this study, we examined whether controlling the freezing storage temperature at which frozen fish meat is stored before thawing can help maintaining the pH and quality of thawed meat. We investigated the changes in the pH and quality of thawed bigeye tuna (Thunnus obesus) meat following storage under different temperatures. During thawing, storage temperature was increased from approximately −50°C to −10°C and maintained for several days. This thawing method has been suggested to be effective not only in the suppression of thaw rigor and drip loss, but also in maintaining high pH in thawed meat. In the present study, frozen bigeye tuna meat was stored at −10°C for 0 to 10 days and then thawed rapidly. Changes in the contents of NAD and ATP before and after thawing were examined, and the conditions necessary for the maintenance of pH were investigated. As a result, the content of NAD decreased below 0.2 µmol/ g when stored at −10 C for more than 2 days. After thawing, meat pH remained high (>6.5) during storage at 3°C for 7 days. The observed maintenance in pH would likely result in a reduction in anaerobic glycolysis and subsequent suppression of ATP degradation and lactic acid synthesis because of NAD reduction. These phenomena could contribute to the maintenance of meat pH after thawing. The suppressive effect of pH decrease was observed regardless of thawing speed. Furthermore, our result from sensory evaluation suggested that thawed tuna meat with high pH improved texture as Sashimi.
The authors developed a finned-tube evaporator to improve efficiency of CO2 refrigerant heat pump water heater by decreasing tube diameter of the evaporator. Number of refrigerant passes was increased from 3 in a conventional model to 6 in the test model to prevent pressure drop from increasing. The authors evaluated the influence on the thermal conduction between adjacent refrigerant tubes through fins and inlet airflow maldistribution. Performance of the evaporator was also evaluated in the winter condition. As the result, the authors revealed that an interlaced circuitry could compensate for the both influence and equalize refrigerant temperature profile. In addition, the authors showed that the circuitry could maintain high outlet pressure of the evaporator in a high superheat region where outlet superheat ratio of the evaporator was more than 0.6. Outlet pressure and superheat ratio of the evaporator increased by 40kPa and 0.7, respectively, in the operating point of the heat pump cycle.
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.
A method using a splitter plate for improving the heat transfer performance of a cooling tube under frosting condition were proposed in this study. Fundamental experiments to validate the method was conducted. A bare cooling tube, a cooling tube with splitter plate and cross fin-tube were tested. Two splitter plates were prepared, which had 20 and 40 mm in length, while the diameter of the cooling tube was 20 mm. The heat transfer performance and pressure loss were evaluated. The temperatures of the coolant were -20 and -196 °C. The results showed that the cooling tube with a splitter plate increases the heat transfer performance without increasing the pressure loss. Consequently, the splitter plate increases the heat transfer rate per a pressure loss coefficient under frosting condition.
This study experimentally investigated the heat transfer and pressure drop characteristics for evaporation and condensation flows of R245fa inside a horizontal smooth tube. The test smooth tube was a copper tube with an inner diameter of 8.32 mm. Evaporation and condensation flows were measured at saturation temperatures ranging from 30– 40 °C and 40–60 °C, respectively, at mass velocities of 50–300 kg/(m2 s). At the same saturation temperature, the differences in the frictional pressure drops of the evaporation and condensation flows were small. Frictional pressure drop increased with increase in mass velocity and vapor quality and decrease in saturation temperature. Similarly, heat transfer coefficients increased with increase in mass velocity and quality and decrease in saturation temperature. The flow patterns inside the tube revealed significant differences in the heat transfer characteristics of evaporation and condensation flows. Further, the experimentally obtained frictional pressure drops and heat transfer coefficients for evaporation and condensation flows were compared with those estimated using correlations reported in the literature. The frictional pressure drops for the evaporation and condensation flows of R245fa and the evaporation heat transfer coefficients were consistent with the previous correlations. Several correlations of condensation heat transfer coefficients tended to be underestimated at low saturation temperatures and high mass velocities in high-quality-region-dominated forced convection. Therefore, a new correlation that considers the gas–liquid density ratio and flow patterns was proposed.
In the present study, the characteristics of both flow and heat transfer in a pharyngeal cooling cuff for the treatment of brain hypothermia were investigated experimentally and analytically. The pharyngeal cooling cuff, which is a balloon-like structure placed in the pharynx, was developed for medical purposes. As a method for controlling the brain temperature, cooling water, which is physiological saline at 5¡C, is injected into the cuff in order to cool the common carotid artery, which is adjacent to the pharynx. In this study, a three-dimensional numerical simulation was carried out to investigate both the flow velocity and heat flux distribution in the cuff. Furthermore, the heat transfer characteristics between the cuff wall and cooled water in the cuff were determined. The simulation results indicate that the behavior of the flow characteristics and heat transfer characteristics was strongly affected by injection velocity of the cuff.
Antifreeze proteins (AFPs) discovered in various organisms living in sub-zero temperature environmnets are known to inhibit ice growth. Recently, there is growing interest in the use of AFPs in various applications. When a single crystal of ice is grown in fish AFP solution, numerous pits consisting of pyramidal planes are formed on the basal plane. In this study, we observed pit formation on the basal plane of ice in 0.5 mg/mL AFP type III solution. We found a few phenomena which was not observed in 5 mg/mL AFP type III solution. For example, pit formation was scarcely observed on molecularly rough surfaces of the basal plane in the 0.5 mg/mL solution, whereas in the 5 mg/mL solution, many pits formed randomly on molecularly rough surfaces. This difference is probably due to the concentration dependence of the adsorption rate and adsorption density of the AFP molecules on ice surfaces.
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.
A room-temperature magnetic refrigerator is attractive that does not use HCFC or its alternatives. It is expected that a wide temperature range can be get by packing multiple magnetic materials in active magnetic refrigerator (AMR) ducts. We focus on a temperature span that is difference between temperature of hot end and cold end when manganese-based magnetic materials are used. These materials have a large entropy change per unit volume, while the temperature range in which to show a large effect is relatively small. In order to investigate the temperature span, temperature distribution of inside AMR duct was measured. Experimental results show that larger temperature span can be obtained for the case of using multiple magnetic materials than that of using a single material. It is confirmed that when the large temperature span is obtained, the temperature distribution in the AMR duct corresponds to the temperature range in which the respective materials show a large magnetic entropy change.
We applied freezing for enrichment of functional components in soybean. Water-soaked soybeans were frozen at –20, –80 or –180 Co . The radius of Cole-Cole plots decreased with decreasing the freezing temperature. Concentrations of -aminobutyric acid (GABA) as the functional compounds in water-soaked soybeans increased during storage. GABA content in water-soaked and frozen-thawed soybeans increased rapidly during storage rather than untreated ones. Kinetic analysis of GABA production in frozen-thawed soybeans indicated that GABA generation production was promoted by the increase in apparent glutamic acid decarboxylase activity associated with the decrease in pH during storage.
Numerical simulations and magnetic resonance imaging (MRI) measurements have been carried out for a better understanding of the behavior in ice crystal growing after breaking of super cooling condition in aqueous solutions. The numerical simulations showed that a fast cooling from outside caused ice nucleation from the outer edge and the expansion of bulky ice crystal, on the other hand, a slow cooling showed ice nucleation from inside and expansion of fibrous ice crystal. Temperature measurements and MRI measurements for a phantom test sample with cylindrical double layer structure showed that frisky ice crystals were outbreak throughout the outer layer inducing the temperature increase up to 0 degree after the breaking of super cooling condition and the inner layer stayed as a liquid at the lower temperature, and after that, bulk ice crystals were expanded from the surface of the inner part in outer layer causing the increase of temperature of inner part.