Identification of a Tissue Inhibitor of Metalloproteinase-2: An Endogenous Inhibitor of Modori-Inducing Insoluble Metalloproteinase from Yellowtail Seriola quinqueradiata Muscle.

The existence of an endogenous protease inhibitor (EPI) was expected from the comparison of the gel properties between washed and nonwashed yellowtail surimi gels. A possible candidate, tissue inhibitor of metalloproteinase-2 (TIMP-2), was partially purified from the soluble fraction of yellowtail muscle, and an 18 kDa protein band was detected by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions and western blot analysis. Its N-terminal amino acid sequence was determined as XSXSPAHPQQAF, with high homology to TIMP-2 from other fish species, suggesting that it was identified as yellowtail TIMP-2. Subsequently, full-length cDNA of two isoforms (TIMP-2a and TIMP-2b) was successfully cloned from yellowtail muscle. The N-terminal sequence of purified TIMP-2 completely corresponded to TIMP-2b. When the surimi gel quality decreased after spawning, the mRNA expression of TIMP-2b also decreased. Human TIMP-2 could inhibit autolysis of myofibrillar proteins from yellowtail muscle. Thus, TIMP-2b was considered the major EPI of the modori-inducing insoluble metalloproteinase in yellowtail muscle.

Influence of the interposition of pink muscle fibers in the dorsal ordinary muscle on the postmortem hardness of meat in various fishes.

We previously showed that the tenderization of ordinary muscle during ice storage is affected by the interposition of pink muscle fibers in the ordinary muscle. However, little is known about whether or not the interposition of pink muscle fibers affects the hardness of raw fish meat. To clarify the influence of the interposition of pink muscle fibers in the dorsal ordinary muscle on hardness of meat, the breaking strengths and the fiber types of the dorsal ordinary muscle of eight fish species (a total of 37 specimens) were discriminated. The breaking strengths among fish species were within a range of 6.5-19.1 N/cm2 . Pink muscle fibers were found in the dorsal ordinary muscle of six out of the eight fish species ranging from 0.0 to 56.0% in quantity ratio, and 0.0 to 19.3% in area ratio, respectively. The quantity ratio and area ratio of pink muscle fibers in the dorsal ordinary muscles of all eight fish species samples positively correlated with the breaking strength. Relative to the quantity ratio (p < .05), the area ratio (p < .02) of pink muscle fibers was more representative of postmortem texture hardness. In conclusion, the high interposition ratio of pink muscle fibers in ordinary muscle could potentially improve the postmortem hardness, the texture, and even the flesh quality of raw fish meat.

Application of Bio-Impedance Analysis to Estimate the Condition of Yellowtail (Seriola quinqueradiata) Muscle at Different Storage Temperatures.

Changes in impedance at 2 kHz, adenosine triphosphate (ATP) content, and muscle contraction were evaluated in yellowtail during 0 (ice), 5, 10, 15, and 20°C storage. Histological changes during ice storage were also measured. At any temperature, although impedance increased with both rigor mortis and ATP consumption during early storage, it began to decrease rapidly when ATP was almost depleted. Moreover, temporarily increasing impedance had a strong relationship with ATP content; decreasing impedance had a significant correlation with storage temperature after ATP depletion. Furthermore, impedance increased with narrowing of intercellular spaces when sarcolemma was intact and decreased with expansion of intercellular spaces when sarcolemma was leaky. Meanwhile, changes of sarcolemma and intercellular spaces were accompanied by ATP change. Thus, ATP is one significant physiological factor for impedance change, and temperature greatly influenced impedance after depletion of ATP. Results suggest that impedance analysis can be used as a convenient and nondestructive method to diagnose condition of tissue at different storage temperatures. Bioelectromagnetics. 2019;40:488-497. © 2019 Bioelectromagnetics Society.

Effect of blood deposition phenomenon on flesh quality of yellowtail (Seriola quinqueradiata) during storage.

We examined the influence of blood deposition on flesh quality of ordinary muscle in yellowtail. This study compared the flesh quality changes in upper and under-sides of yellowtails killed by two different methods: spinal-cord destruction (SCD) with blood removal and suffocation in air without blood removal (SA). The under-sides of the SA group showed the highest values for a*, cathepsin B and B + L activities, the lowest value in breaking strength and the greatest degradation of myosin heavy chain (MHC) among the four groups. However, the values of the SCD-upper group indicated the best flesh quality. In addition, the white blood cells presented the highest cathepsin B and B + L activities among the blood components. These results indicate that blood has the tendency to deposit downward in accordance with the direction of placement. This phenomenon influences the distribution of white blood cells which contain enzymes that accelerate the deterioration of flesh quality. The texture of fish muscle is an important part of the flesh quality. In captured fishery (purse-seine fishery and dragnet fishery), it is impossible to immediately and completely remove blood. Therefore, suffocation in air is the common method after the fish is caught. The commercial value of fish is decreased and the price varies greatly when these fish enter market circulation. In our study, we examined the influence of blood deposition on the flesh quality of yellowtail during storage. The degradation of structural proteins accelerated in the deposited blood which contain proteases. The movement and deposition of blood caused the difference of quality on both sides, which seriously affected the quality of fish during preservation. Our study has some theoretical guidance for muscle softening and give a better understanding of the adverse effect of blood during preservation.

The effect of ice crystals formations on the flesh quality of frozen horse mackerel (Trachurus japonicus).

It is known that the formation of ice crystals has a negative impact on the flesh quality of frozen meat. This study focuses on how the formation of ice crystals in the dorsal ordinary muscle affects the flesh quality of frozen horse mackerel (Trachurus japonicus). Freeze-thawed muscle specimens (F-TMS) of horse mackerel were first stored at -24C and then thawed. The K-value, expressible water, breaking strength of unfrozen muscle specimens (UMS) and F-TMS, and histological structure (light microscope [LM], scanning electron microscope [SEM] of UMS, frozen muscle specimens [FMS], and F-TMS) were investigated. K-values were higher in the F-TMS than in the UMS, and the increasing rate of K-value in F-TMS was approximately 1.4-fold higher than UMS. Similarly, the percentage of expressible water was higher in the F-TMS than in the UMS. The breaking strength of the UMS decreased with storage period, but it remained at a higher level than that of F-TMS. Numerous ice crystal formations in muscle cells of FMS and small interstices between cells of F-TMS were observed under LM. Moreover, we observed a relatively collapsed honeycomb structure of the extracellular matrix (ECM) under SEM, and found that collagen fibril networks of endomysiums became looser after thawing. Therefore, ice crystals contribute to vulnerabilities in the ECM. These results suggest that a decrease of freshness and the degradation of physical properties caused by ECM destruction may be due to the formation of ice crystals in muscle structures during freezing, leading to the deterioration of flesh quality during storage. PRACTICAL APPLICATIONS: The flesh quality deteriorated after thawing on the basis of degradation of physical properties. Moreover, it could be presumed that the K-value increase was exacerbated by ice crystals, and the decreasing speed of chemical freshness was sped up accompanied by ice storage after thawing. Thus, the formation of ice crystals, which destroyed the muscle cells and structures, may be one of the dominant factors causing the deterioration in the flesh quality.

Dietary Supplementation with Isoflavones Prevents Muscle Wasting in Tumor-Bearing Mice.

Proinflammatory cytokines contribute to the progression of muscle wasting caused by ubiquitin-proteasome-dependent proteolysis. We have previously demonstrated that isoflavones, such as genistein and daidzein, prevent TNF-α-induced muscle atrophy in C2C12 myotubes. In this study, we examined the effect of dietary flavonoids on the wasting of muscle. Mice were divided into the following four groups: vehicle-injected (control) mice fed the normal diet (CN); tumor-bearing mice fed the normal diet (TN); control mice fed the isoflavone diet (CI); and tumor-bearing mice fed the isoflavone diet (TI). There were no significant differences in the intake of food or body weight gain among these four groups. The wet weight and myofiber size of gastrocnemius muscle in TN significantly decreased, compared with those in CN. Interestingly, the wet weight and myofiber size of gastrocnemius muscle in TI were nearly the same as those in CN and CI, although isoflavone supplementation did not affect the increased tumor mass or concentrations of proinflammatory cytokines, such as TNF-α and IL-6, in the blood. Moreover, increased expression of muscle-specific ubiquitin ligase genes encoding MAFbx/Atrogin-1 and MuRF1 in the skeletal muscle of TN was significantly inhibited by the supplementation of isoflavones. In parallel with the expression of muscle-specific ubiquitin ligases, dietary isoflavones significantly suppressed phosphorylation of ERK in tumor-bearing mice. These results suggest that dietary isoflavones improve muscle wasting in tumor-bearing mice via the ERK signaling pathway mediated-suppression of ubiquitin ligases in muscle cells.