Abalone (Hariltis discus): Seasonal Variations in Chemical Composition and Textural Properties

Seasonal changes in adenosine 5′-triphosphate, total free amino acids, and total oligopeptides in abalone meat were analyzed. Levels were higher in summer and lower in winter. In both seasons, the most abundant free amino acid was taurine followed by arginine, glycine, glutamine, and glutamic acid. The largest peptide-bond amino acid was glutamic acid + glutamine. The collagen content decreased in summer and increased in winter. The breaking stress values of the meat were low in summer and high in winter, indicating that summer abalone would be more tender. Scanning electron microscopy revealed the collagen network was more compact in winter.     

Carp Sarcoplasmic Reticulum Changes Due to Heat Treatment

Electron microscopy revealed that heat treatment in the range 35–55°C caused no observable change in membrane structures of the sarcoplasmic reticulum (SR). Proteins with molecular weights about 200 and 400 kDa, (probably dimers and tetramers of Ca²⁺-ATPase, respectively) were observed in SDS-PAGE when the light SR was treated at 49 and 55°C respectively. Ca²⁺ leakage from the SR was markedly enhanced with increasing temperatures, especially for the heavy SR. Results suggest that the decrease of Ca²⁺ uptake ability following heat treatment is at least partly caused by the acceleration of Ca²⁺ leakage together with irreversible denaturation of Ca²⁺-AT-Pase protein.     

EFFECT OF FROZEN TEMPERATURE ON AUTOXIDATION AND AGGREGATION OF BLUEFIN TUNA MYOGLOBIN IN SOLUTION

The effect of frozen storage temperatures in the range of -3C to -80C on the autoxidation and aggregation of bluefin tuna oxy- and deoxy-myoglobin (Mb) in solution was examined. Mb solution was kept frozen at various temperatures after prefreezing by dry ice-acetone and examined for autoxidation rate constant and aggregation ratio. The temperature-dependency of these two parameters showed the highest values at -10C with both oxy or deoxy forms. The autoxidation rate constant of deoxyMb was higher than that of oxyMb between -6C and -20C, while the reverse trend was observed at lower temperatures. These results suggest that the structure of Mb was perturbed through freezing resulting in promotion of the autoxidation and aggregation of Mb simultaneously. These results could explain the observation that deoxyMb in the inner portion of tuna flesh discolors faster than oxyMb in the surface portion in the temperature range of -3C and -20C.     

Heat-Induced Tendering of Turban Shell (Batillus cornutus) Muscle

The foot, opercular and visceral muscles were excised from the turban shell Batillus cornutus, and their heat-induced changes in toughness and ultrastructure were compared. When heated up to 30°C, the toughness of foot muscle decreased in the upper and middle regions, but increased in the lower region. The toughness of these three regions decreased at temperatures between 50-70°C, where collagen might be denatured. Some changes in toughness were also observed in the opercular muscle by heating up to 30°C, whereas the toughness of visceral muscle remained unchanged over a wide range of temperature. Transmission electron microscopy showed that the intrinsic structure of collagen fibrils in each muscle was lost at 60°C, with partial swelling.     

Autoxidation of Bluefin Tuna Myoglobin Associated with Freezing and Thawing

Bluefin tuna oxymyoglobin (oxyMb) solutions were frozen either quickly at ?80°C or slowly at ?2O°C, thawed, and the metmyoglobin (metMb) to total myoglobin (Mb) ratio (metMb%) determined. When quick freezing was applied, autoxidation was clearly pH-dependent, with a minimum (metMb%, 15–40) at around pH 5.9–6.3. When slowly frozen and thawed, on the other hand, tuna Mb generally showed an extremely high metMb%. Freezing and thawing partially insolubilized tuna Mb, depending upon pH. The Mb showed the minimum ratio of insolubilization at pH 6–6.3 again. Insolubilization of tuna Mb was markedly accelerated by NaCl.     

ATP and Creatine Phosphate Breakdown in Spiked Plaice Muscle during Storage, and Activities of Some Enzymes Involved

The onset of rigor-mortis of plaice Puralichthys olivaceus spiked at the brain started much faster at 0°C than at 10°C. Correspondingly, ATP and creatine phosphate breakdown and lactic acid accumulation in the muscle were faster at 0°C. ATP concentration was constant at 5 μmol/g until creatine phosphate decreased from the initial conccntration at around 20 μmol/g to 5 μmol/g, irrespective of storage temperature. Simultaneously, lactic acid accumulated, slowly at first, until ATP concentration started decreasing, and then quickly accompanying the full-rigor state. Activities of the enzymes involved in ATP and creatine phosphate consumption-myofibrillar and sarcoplasmic AT-Pases and creatine kinase-were temperature-dependent, and decreased with decrease in temperature.     

Short Thermal Treatment Effect on Carp Myofibril and Sarcoplasmic Reticulum: Possible Mechanisms in Rigor Mortis Acceleration by "Arai" Treatment

Inorganic γ-phosphate liberation from adenosine 5′-triphosphate (ATP) by carp myofibrillar ATPase was measured at 0-60°C to elucidate mechanisms in rigor mortis acceleration of sliced carp muscle during washing at a moderately high temperature. ATP splitting within 20 sec in the presence of 5 mM MgCl₂ plus 0.25 mM CaCl₂ was maximal at 45°C, which agreed well with the commercially adopted condition for preparing carp “arai” muscle. In addition, the maximum Ca²⁺ uptake by sarcoplasmic reticulum was observed at 30°C and decreased at higher temperatures. The acceleration of carp muscle rigor mortis at around 45°C was suggested to be partly due to enhancement of myofibrillar Mg²⁺-ATPase activity by increase of intracellular Ca²⁺ concentration.     

Effect of Storage Temperature on Rigor-Mortis and ATP Degradation in Plaice Paralichthys olivaceus Muscle

Live specimens of the plaice Paralichthys olivaceus were spiked at the brain, stored at various temperatures ranging from 0° to 20°C and examined for changes in rigor tension and ATP degradation in the muscle. The ATP degradation rate was clearly slower at 5–15°C than at WC, resulting in retardation of rigor- mortis onset at the former temperatures. Lactic acid accumulation in the muscle correlated well with the decrease of ATP. The muscle showed an ATP concentration of 3 μmol/g and “rigor index” (full rigor = 100%) at 30% when lactic acid increased up to 30 μmol/g at most storage temperatures. The muscle showed full rigor when ATP completely disappeared and lactic acid attained the maximum plateau (40–50 μmol/g).     

Temperature-Dependency of Rigor-Mortis of Fish Muscle: Myofibrillar Mg2+-ATPase Activity and Ca2+ Uptake by Sarcoplasmic Reticulum

Myofibrillar Mg²⁺-ATPase activity of plaice and red sea bream increased with increase in reaction temperature and Ca²⁺ concentration. However, temperature decrease tended to lower Ca²⁺ sensitivity of Mg²⁺-ATPase activity. While it was assumed that spiked fish muscle was relaxed and the myofibrillar Ca²⁺ concentration was low, the progress rate of rigor-mortis correlated well with Mg²⁺-ATPase activity in the presence of a few micromolar Ca²⁺ at 0°C. Correspondingly, it was found that Ca²⁺ uptake by plaice sarcoplasmic reticulum decreased with the decrease in reaction temperature. These results strongly suggest the acceleration of fish rigor-mortis at 0°C is due to the increase of Ca²⁺ concentration in myofibrils during storage at this temperature.     

EFFECT OF SLAUGHTER METHOD ON DEGRADATION OF INTRAMUSCULAR TYPE V COLLAGEN DURING SHORT-TERM CHILLED STORAGE OF CHUB MACKEREL SCOMBER JAPONICUS

The present paper demonstrates that a nonstntggling slaughter method can delay degradation of type V collagen in meat of chub mackerel Scomber japonicus and softening of the meat during postharvest chilled storage. The fish were slaughtered by piercing a knife into nape (nonstruggling method) or by leaving on ground (struggling method) and then stored in an ice box. Sensory study revealed that the postharvest softening of the meat was moderated at 4 and 8 h by the non‐struggling slaughter method in comparison with the struggling method. On the basis of the specific solubilization of type V collagen and reduced tyrosine content in it, a cleavage of the nonhelical regions (telopeptides) of the type V collagen occurred during the chilled storage in the fish slaughtered by the struggling method. The degradation of type V collagen was also slower in the meat of the fish slaughtered by the nonstruggling method, which can be directly linked to the moderation of the postharvest softening.