Denaturation Kinetics of Myofibrillar Proteins in Bovine Muscle

Differential scanning calorimetry was used to monitor the thermal denaturation kinetics of myofibrillar proteins in bovine muscle at pH 5.6. The activation energy, pre-exponential factor, rate constant and mean life time for each transition were calculated by means of a dynamic method. The kinetic values and the proposed reaction order (n= 1) were confirmed applying an isothermal method as a test. The position of the endothermal peaks proved to be pH dependent. Evidences suggest that peak III is a result of actin denaturation and possibly other thin filament proteins. Peaks I and II would represent the thermal transition of thick filaments. The number of bonds involved in each transition were estimated.     

Thermal Denaturation and Aggregation of Proteins in Minced Fish as Studied by a Thermomechanical Method

A thermomechanical method of heating and mixing, was developed to study directly protein denaturation and aggregation in minced fish. It is based on simultaneous and continuous measurement of torque and temperature in a meat sample mixed while being heated. The torque and temperature were continuously recorded. From curves thus obtained, thermal denaturation temperatures of minced samples from 6 marine fish species were determined. The curves showed 4-6 peaks at 32-38°C, 44-46°C, 52-56°C, and 62-75°C, presumably corresponding to denaturation of myosin, actomyosin, sarcoplasmic proteins, and actin, respectively. The temperature range of peak 1 was 4-5°C higher in fatty fish (herring, mackerel) than in lean fish (cod, blue whiting).     

Shrinkage in Fish Muscle During Drying

Shrinkage of rectangular slabs of ocean perch (Sebastes marinus) in all three dimensions during air drying at 24.5°C, relative humidity 35% and velocity 35.6 m/min was determined. Percent change in dimensions with volume fraction of water was measured. It was observed that the dimension along the major axis of muscle fibers (length in this case) shrinks far less than the other two dimensions. Maximum shrinkage in length was 20%, while for width it was 50.5% and for thickness, 50.6%. At 95% confidence level, there was no significant difference between thickness and width shrinkage.     

Capillary Zone Electrophoresis of Fish Muscle Sarcoplasmic Proteins

A capillary zone electrophoresis (CZE) method for rapid separation of fish muscle sarcoplasmic proteins (SAJR) was developed using a highionic-strength phosphate buffer and an untreated, fused silica capillary (20 μm i.d. X 20 cm). Changes in pH between 6.6-7.5 resulted in differences in mobility, separation factors, and number of SAR moieties. An optimal SAR profile was obtained at pH 7.4. When used to monitor frozen storage changes in SAR from cod (Atlantic, Ling, Pacific) and pollock fillets, the procedure indicated both species differences and low-and high- molecular-weight frozen storage changes. CZE is an effective screening/quantification alternative to conventional electrophoresis and/ or HPLC because it is fast (<10 min), simple, sensitive, precise, and readily automated.     

Salt-Induced, Low-Temperature Setting of Antarctic Fish Muscle Proteins

Freshly prepared salted pastes (2.5%, w/w NaCl) of muscle tissue of the Antarctic fishes Pagothenia borchgrevinki (white muscle) and Dissostichus mawsoni (red and white muscle) rapidly formed cold-set gels. Set times were minutes rather than the hours required to cold-set salted pastes of fish from cold- temperate waters. Cold-setting was related to habitat temperature and the stability of fish muscle myosin, the protein responsible for gel formation.     

Glutathione Peroxidase Activity During Storage of Fish Muscle

Activity of fish muscle glutathione peroxidase, which presumably protects muscle from oxidative deterioration during storage and processing, was found in both Japanese jack mackerel and skipjack tuna. Activity of the peroxidase and level of reduced glutathione (enzyme substrate) decreased during 5 days storage at 4°C. Lipid hydroperoxides were substantially formed in the fish muscles during the storage.     

Lithium Chloride as a Preferred Extractant of Fish Muscle Proteins

Lithium chloride yielded better extraction of fish muscle protein than sodium or potassium chloride under most conditions. In addition, constancy of extracted protein was better with lithium compared to potassium or sodium chlorides with respect to blending time, salt concentration, pH, temperature and foaming. With stored red hake muscle, LiCl was superior to NaCl with better extractability of protein and more linear reduction of extractability with storage time. Evidence indicated the superior performance of lithium compared to sodium was due to stabilization by lithium chloride of fish proteins towards denaturation.     

Collagenase Effect on Thermal Denaturation of Intramuscular Collagen

We have investigated the action of a collagenase from Clostridium histolyticum on the thermal denaturation parameters (AH and initial temperature of denaturation [qt]) of bovine intramuscular collagen. Collagens exhibiting various degrees of reticulation were extracted from calves, steers and cull cows pectoralis profundis muscle. Collagenase treatment induced a decrease in the enthalpy of denaturation of calf and steer collagens inversely related to animal age, but no change was observed for cow's collagen. Irrespective of the degree of reticulation, collagen breakdown by the collagenase led to the appearance of another peak of denaturation starting at a lower temperature (55–57°C) than that of intact collagen (62–63°C).     

Gelling Properties of Tyrosinase-Treated Dairy Proteins

Protein-based viscous gels can augment or replace carbohydrate-based ones for specific nutritional formulations such as in reduced calorie or low-fat food applications. In this study, slurries of whey protein isolates and calcium caseinate mixed with alginic acid (20% T.S.) were subjected to high-shear homogenization (microparticulation) at 27,000 rpm for 2, 3, 4, and 6 min. The resulting slurries were incubated with mushroom tyrosinase (E.C. 1.14.18.1) at levels of 3, 6, and 9 mg/100 g for 15, 30, and 60 min to facilitate gel formation of the alginic acid with the homogenized dairy proteins. The results indicate that the time of high-shear homogenization had significant (P < 0.05) effect on the viscosities of the gels. Highest gel viscosity was obtained with 6 mg tyrosinase at 60 min, but increases in gel viscosity depended on time of shear, with 2 and 4 min shear resulting in higher viscosity (484 and 6,143 cP) and stronger complex viscosity (49 and 38 Pa.s at 1 rad/s), respectively, compared to the control (69 cP) and (12 Pa.s at 1 rad/s). Gels were stable in refrigerated storage up to 240 h, strengthened with time of refrigeration storage, and became significantly more viscoelastic. Optimal viscous properties were obtained at 4 min microparticulation, 60 min incubation, and 6 mg tyrosinase treatment.     

Differential Insolubilization of Red Hake Muscle Proteins During Frozen Storage

Contractile proteins were more susceptible to insolubilization than sarcoplasmic proteins. Some proteins of both the sarcoplasmic and contractile fractions were more susceptible than others. Proteins of molecular weights 102K-, 82K- and 73K-daltons in sarcoplasmic fraction were most susceptible while myosin heavy chain, M-proteins, tropomyosin and troponins I and C were, in descending order, the most susceptible among contractile proteins.     

Carp Natural Actomyosin: Thermal Denaturation Mechanism

Structural changes of actomyosin, the major protein of muscle, on heating have been estimated on ATPase activity. We investigated carp actomyosin molecule changes on heating based on biophysical and biochemical techniques. Actomyosin molecules began to unfold at ～30°C. Hydrophobic amino acid residues and SH groups, which had been inside the molecule, emerged to the surface. Because of hydrophobic interactions and disulfide bonds, actomyosin molecules formed aggregates. At > 40°C, a part of myosin molecules was dissociated from actin filaments. Thus, dissociated myosin and the myosin-lacking molecules co-existed. In addition, fragmentation of actin filaments was observed, which was associated with the dissociation of myosin molecules. At ≥ 60 °C actomyosin molecules formed larger aggregates, in which no filamentous shape was observed. This aggregation occurred mainly by formation of SS bonds.     

Fractionation of Muscle Proteins of Fresh Water Fish and Changes during Iced Storage

SUMMARY: Fractionation of muscle proteins of four varieties of fresh water fish after storage in ice was carried out by serial dilution of a buffer extract of ionic strength 0.55. Precipitation of actomyosin was complete at an ionic strength of 0.175 and fibrillar fraction at 0.05. In Ophiceohalus sp. the initial solubility of proteins was 91-93%. The solubility fell to 82% by the 5th day and increased on further storage up to 13 days. Further storage indicated a fall in solubility. The fall in solubility on the 5th day coincided with the highest level of actomyosin and maximum rigor rigidity of the round fish. Actin solubility in buffer showed the same pattern as solubility of total proteins. The quantity of actin not reconvertible into f-actin showed an increase during storage. Viscosity of buffer extracts showed an increase during development of rigor and decrease on further storage as reflected by level of preformed actomyosin.     

Post-Mortem Softening of Fish Muscle During Chilled Storage as Affected by Bleeding

Bleeding caused the delay of muscle softening in yellowtail, horse mackerel, and striped jack, which are pelagic fish. Conversely, bleeding had no influence on the muscle firmness of red sea bream, flatfish, and rudder-fish, which are demersal fish. Transmission electron microscopy showed delay of degradation of pericellular collagen fibrils in bled yellowtail and horse mackerel. Striped jack showed slower weakening of the pericellular connective tissue in a compression test. However, the demersal fish had no structural difference due to bleeding. These results indicate that removal of blood could delay collagen fibril degradation and muscle softening of pelagic fish.     

Role of Trimethylamine Oxide in the Freeze Denaturation of Fish Muscle–Is It Simply a Precursor of Formaldehyde?

A possible alternative role for trimethylamine oxide (TMAO) in fish muscle “freeze denaturation” was tested. Since TMAO is known to stabilize proteins against conformational change, its enzymatic removal during frozen storage could cause protein destabilization and aggregation. However, addition of TMAO to muscle tissue did not influence the rate or extent of “freeze denaturation” as assessed by protein solubility measurements.     

Thermal Transitions of Admixed Starch/Fish Protein Systems During Heating

The thermal transitions of starch-fish protein mixtures were investigated by a thermal scanning rigidity monitor technique and differential scanning calorimetry. Three transitions due to protein denaturation and one transition due to starch gelatinization were identified by both techniques during thermal processing of these mixtures. The gelatinization of starch caused an increase in rigidity of the system to a degree dependent upon the starch type. Thermal transitions of starch and fish protein seemed to proceed independently in mixture systems. However, the presence of salt and sucrose, necessitated by the inclusion of fish protein, caused starch gelatinization to shift to higher temperatures.     

Denaturation Kinetics and Aggregation Mechanism of the Sarcoplasmic and Myofibril Proteins from Grass Carp During Microwave Processing

Optimizing the physicochemical properties of microwave-cooked meat needs a better understanding of the mechanisms responsible for protein changes. This paper explored the causes of aggregation of the denatured fish protein in ready-to-eat food by determining the changes in sarcoplasmic and myofibril proteins, which includes the effects of different microwave power levels (300, 600, and 900 W) and heating times (0–60 s) on the aggregation kinetics and physiochemical properties. The determination of aggregation kinetics that accurately describes microwave cooking characteristics is crucial for the optimization of operating parameters, performance improvement of the cooked food system, and product quality. The aggregation rate and turbidity of proteins increased with increasing microwave power and time. A negative correlation was observed between the protein solubility and microwave power and time. Protein aggregation induced by microwave showed a reliable and reproducible characterization of particle size distributions. At longer microwave heating time or higher microwave power, these protein particles formed larger aggregates.