Thermal Transitions in Myosin-ANS Fluorescence and Gel Rigidity

Thermal transitions (Tr) in myosin were monitored during constant rate heating with a thermal scanning rigidity monitor (TSRM) and a fluorescent probe, 1-anilino-naphthalene-8-sulfonate (ANS). The Tr values from fluorescent probe measurements were 37°C, 44°C, and 44°C for tilapia, rabbit, and chicken myosin-ANS, respectively. Three Tr values at 43°, 49°C, and 55°C were observed in TSRM measurements of tilapia myosin gelation, whereas a single Tr was observed in rabbit and chicken gelation at 48°C and 49°C, respecitvely. In tilapia myosin, KCl concentration and pH significantly influenced the TSRM but not the fluorescence thermograms. These results indicated that a prerequisite change occurred in the hydrophobic character of myosin just prior to the onset of gelation.     

Thermally Induced Gelation of Native and Modified Egg White-Rheological Changes During Processing; Final Strengths and Microstructures

The heat-induced gelation of native egg white (EW) and egg white modified with succinic anhydride (SEW) or oleic acid (OEW), by addition of 15 moles of reagent/50000g protein, was evaluated. Rigidity modulus (G) and mechanical energy damping were continuously monitored during heating of the samples from 5 - 95°C in a nondestructive temperature-controlled thermal scanning rigidity monitor (TSRM). A measurable increase in G and decrease in energy damping were observed at lower temperatures for OEW than for EW. In SEW the measurable rheological transitions occurred at the highest temperature ranges. Failure strength of the cooked products (gels) evaluated using torsion and uniaxial compression tests revealed large differences due to treatments. Micrographs of gels showed apparent structural differences among treatments.     

GELATION KINETICS of MEAT EMULSIONS CONTAINING VARIOUS FILLERS DURING COOKING

A cylindrical shaped thermal scanning rigidity monitor (TSRM) was developed to determine shear rigidity modulus of meat batters during cooking. A meat fatprotein ratio of 1.8, moisture content of 62% and 8.6% filler were used. the fillers were buttermilk powder, corn starch, micro-crystalline cellulose, modified corn starch, modified wheat flour, soy-protein concentrate and whey-protein concentrate. Plots of rigidity modulus versus product-temperature showed two major thermal transitions. the first and most important transition (53 to 61°C) was due to myosin gelation. the second transition (64 to 69°C) was ascribed to the collagen softening. the maximum rigidity-temperature slopes of 0.60 to 1.02 kPa/°C occurred after the first transition.     

Gelation and Thermal Transitions in Post-Rigor Turkey Myosin/Actomyosin Suspensions

A myosin/actomyosin mixture (MAM), actomyosin and myosin were isolated from post-rigor turkey. Rheological properties of MAM gels were determined by uniaxial compression. Breast MAM formed gels which were stable at lower protein concentrations (10 and 15 mg/mL) than thigh MAM (20 and 25 mg/mL). Differential scanning calorimetry (DSC) and a fluorescent hydrophobic probe, 8-anilino-l-napthalene sulfonate (ANS), were used to study thermal transitions. One DSC peak was observed in breast and thigh MAM. ANS thermograms showed that thigh actomyosin had a greater transition temperature (Tr) (51.8°C) than breast actomyosin (49.7°C). The ANS Tr was 48°C for both myosins. The difference in gelation appeared to be associated with protein-protein interactions.     

Changes in Physical Properties of Meat Batters During Heating

Techniques for measuring changes in physical properties of meat batters during heating that would be suitable for studying kinetics of gelation were studied. Change in absolute modulus as measured by a dynamic tester was too variable to be useful in studying gelation kinetics. However, differences in consistency show up as significant differences if the absolute moduli of the raw batters. Increase in volume during heating was strictly a temperature effect and the rate of expansion at the same heating medium temperature was the same for a bitter that was gelling compared to a gelled batter in the same mold. Pressure change on heating of a batter at constant volume showed a pattern consistent with expected behavior of proteins on heating. Plots of pressure against temperature were a series of linear sections with the transition points occurring at 33–36°C and at 57–67°C. These temperature ranges are known to start insolubilization of muscle proteins and start solubilizaation of collagen respectively. Plots of unaccomplished pressure change against time on semi logarithmic coordinates was used to calculate a time constant for each stage of the process thereby giving a measure of the rate of gelation.     

Dynamic Viscoelastic Behavior of Natural Actomyosin and Myosin during Thermal Gelation

The changes in viscoelasticity of natural actomyosin and myosin during thermal gelation were investigated by dynamic viscoelasticity measurements. Thermal gelation of natural actomyosin could be divided into four characteristic temperature ranges. The storage modulus increased considerably in the 32–43°C range, decreased sharply in the 43–52°C range, and then increased again in the 52–80°C range. For the thermal gelation of myosin, the storage modulus increased in two steps at two temperature ranges, i.e., 30–41°C and 51–80°C. An increase in the loss modulus was observed at an early stage of each of the two ranges.     

Thermal Transitions of Actomyosin and Surimi Prepared from Atlantic Croaker as Studied by Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) was used to investigate thermal transitions of fish mince (surimi) and actomyosin from croaker. Three endothermic peaks were observed in DSC thermograms of surimi. After addition of salt, transition temperatures shifted to lower temperatures. Preheating samples containing 3% salt at various temperatures showed that 40°C heating caused the first peak to disappear, and preheating at temperatures higher than 50°C caused virtual disappearance of all transition peaks. Low temperature storage (4°C) of samples caused no significant change in thermograms of salted or unsalted surimi over a 5-day storage period. Evidence suggests that changes of fish protein during low temperature “setting” are different from those occurring during high temperature “setting.”     

Influence of Thermal Treatment on Gelation of Actomyosin from Different Myosystems

We analyzed the influence of temperature and heating time on rheological properties, and types of proteins involved in the gelation process of natural actomyosin from pork, chicken, and hake. At low temperatures (40–50°C) hake gels were stiffer than chicken or pork gels (due to setting); at higher temperatures (60°C), actomyosin from all three formed gels with similar rheological characteristics. Types of protein in the different fractions (analyzed by electrophoresis) were consonant with the rheological behavior of the AM gels for each heat treatment and species.     

Dynamic rheological behaviour and biochemical properties of rabbit skeletal actomyosin during storage at 0° C

The relationship between the dynamic rheological properties of heat induced gels of actomyosin (natural actomyosin) and the denaturation of actin in actomyosin during storage without ATP at pH 6.0 and 0°C was investigated using biochemical and dynamic rheological measurements. The complex modulus of gels after heating actomyosin containing 0.5 or 1.5 M KCl (pH 6.0) at 80°C increased with increasing storage time. The dynamic rheological behaviour during heat gelation of actomyosin in 1.5 M KCl indicated that the first rheological transition peak in the 50–53°C range induced by the presence of F-actin gradually disappeared with increasing storage time. However, in 0.5 M KCl, this transition peak clearly remained even after 15 days. The time course of denaturation of actin in actomyosin treated with 1.5 M KCl at pH 6.0 showed an increase in the percent denaturation after the storage was started, and about 100% of the actin became denatured after 21 days. In the case of 0.5 M KCl, unlike 1.5 M, the denaturation of actin occurred quickly within the first 5 days and then did not proceed. A sigmoidal relationship was found between the percent denaturation of actin and the KCl concentration added, the greatest change occurring at KCl concentrations between 0.5 and 1.0 M. The data indicated that the change in the property of actin in actomyosin during storage at low temperature exerts a great influence on the viscoelasticity of heat-induced gels of actomyosin.     

Myofibrillar Protein Gelation: Viscoelastic Changes Related to Heating Procedures

Dynamic Theological properties were investigated during gelation of chicken myofibrillar protein as influenced by heating procedures, Thermal scan (1°C/min) of myofibril suspensions in 0.6M NaCl (pH 6.0) induced a major transition in storage modulus (G′, peak 48°C), preceded by a transition in protein-protein aggregation (46°C) and accompanied by a marked reduction in actomyosin solubility. Preheating at 50°C diminished the transition and resulted in increased final G′value. Isothermal heating produced complex, temperature-dependent Theological changes (G′and phase angles), particularly within 43–58°C. The rheological transitions of myofibrillar protein were probably related to kinetic changes during formation of elastic gel networks. Such Theological data on gel formation can help predict and control muscle food responses to specific thermal processes.     

Thermal Denaturation and Aggregation of Actomyosin from Atlantic Croaker

The denaturation of croaker actomyosin was studied with respect to the important role of coagulation and gelation phenomena in the manufacture of gel-type meat and fish products. Measurements of turbidity (A₆₀₀), viscosity, calcium ATPase activity, total sulfhydryl groups and protein coagulation of croaker actomyosin solutions during heating at a constant temperature increase of 1°C/min revealed no loss of enzymic activity nor evidence of protein aggregation prior to reaching a temperature of 37–40°C, at which point the protein coagulated with corresponding loss of ATPase activity and sulfhydryl groups and an increase in turbidity. The degree of protein coagulation was highly dependent on the protein concentration. An observed increase in the apparent viscosity over the 30–35°C temperature range was postulated to result from interaction of protein molecules due to noncovalent forces.     

Role of F-actin in Thermal Gelation of Fish Actomyosin

The thermal gelation processes of the myosin-natural actomyosin system were investigated to determine the role of F-actin in thermal gelation of actomyosin. The dynamic viscoelastic behavior during thermal gelation changed considerably depending on the (F-actin)/ (myosin) ratio. F-actin gave the viscosity to an actomyosin sol but did not affect the elasticity development occurring in the 30 - 46°C range. The decrease in storage modulus in the 46 - 53°C range was directly induced by the presence of F-actin. The gel of myosin alone showed the highest elasticity, while that of myosin containing a small amount of F-actin had the highest elastic modulus.     

Gelling Properties of Actomyosin from Pre- and Post-Spawning Hake (Merluccius hubbsi)

The biochemical properties and the characteristics of heat-induced gelation of natural actomyosin (NAM) from pre- and post-spawning hake were studied. Mg²⁺ ATPase activity, reduced viscosity and myosin/actin mole ratio of NAM from post-spawning fish were higher than those of pre-spawning ones. Gelation of both actomyosin at 10 mg mL^?1 of protein concentration was optimal at 60°C and pH 6.0. The highest rigidity was reached at 0.40M and 0.44M KCl with NAM from pre and post-spawning hake, respectively. Irrespective of heating temperature, ionic strength conditions and at pH range 5.5–7.5, rigidity of post-spawning hake NAM gels was higher than those of pre-spawning fish. Scanning electron micrographs of pre- and post-spawning hake NAM showed “actin-type” and “myosin-type” ultrastructures, respectively.     

Changes in Physicochemical Properties of Bighead Carp (Aristichthys mobilis) Actomyosin by Thermal Treatment

Physicochemical properties of actomyosin from bighead carp during heat-treatment were investigated. Turbidity, solubility, and surface hydrophobicity showed significant changes from 40–55°C (P < 0.05). Heat-treatment before 45°C could make actomyosin unfold, and the disulfide bonds were formed at temperatures above 45°C. Three enthalpy transitions at 41.2, 61.7, and 63.4°C were found in differential scanning calorimetry thermogram of bighead carp actomyosin. Storage modulus (G′) increased gradually and reached the first peak at 36.5°C and the second peak at 50°C. Myosin suffered conformation changes and lead to aggregation during the heating period.     

HEAT-INDUCED GELATION OF MYOSIN IN THE PRESENCE OF ACTIN

ABSTRACT The rabbit muscle contractile proteins, myosin, actin and reconstituted actomyosin were mixed in 0.1–1.0 M KCl, 20 mM buffers, pH 5.0–8.0, and were tested quantitatively for thermally induced gelation properties by measuring the rigidity (shear modulus) of the system at 20–70°. Scanning electronmicroscopy (SEM) was also used to study the structure of the gels formed by gelation of myosin in the presence of F-actin. Under the standard condition, i.e. at 0.6 M KCl, pH 6.0 and 65°, decrease of the myosin/actin mole ratio to about 1.5–2.0 in the reconstituted acto-myosin system resulted in substantial augmentation of the rigidity of the gel formed. Further decreases in the myosin ratio relative to F-actin reduced the rigidity value of the gel to close to the level of myosin alone. Gel-formability of the reconstituted actomyosin was maximal at pH 5.5–6.0 and between 0.5 and 0.8 M KCl and decreased considerably at other pH values and KCl concentrations. The SEM studies revealed progressive changes in three dimensional ordering as actin concentration in the actomyosin varied. These were in concordance with the results of gel strength.     

Effect of Heating Rate on Meat Batter Stability, Texture and Gelation

The effects of four heating rates (0.31, 0.51, 1.22, and 1.62°C/min) on the gelation, stability and texture of meat batters containing 2.5 and 1.25% salt were studied. In general, slower heating rates resulted in higher modulus of rigidity (G) values, and salt reduction resulted in lower G values. All the low salt treatments, except the 1.62°C/min treatment, showed a structural breakdown (above 67°C) when the scanning rigidity monitor was used. However, in the texture profile analysis (samples cooked to 50, 60 and 70°C) no structural breakdown was observed. Therefore, special care should be given to interpreting gelation profile results.     

On the temperature reversibility of the viscoelasticity of acid-induced sodium caseinate emulsion gels

Viscoelastic properties of acid-induced sodium caseinate emulsion gels have been investigated using a controlled shear stress rheometer. Gelation was introduced by addition of acidulant glucono-δ-lactone (GDL) at three different temperatures (5, 25 and 45°C). It was found that the gelation temperature has a significant effect on the rate of gelation and on the dynamic moduli of the emulsion gels. The rheology of these emulsion gels was investigated over the temperature range 5–45°C. The viscoelasticity of the emulsion gel prepared at 45°C was temperature reversible, suggesting that the temperature change only affects the strength of physical bonding within the network and not the gel microstructure. In contrast, the temperature-dependent viscoelasticity of the emulsion gel prepared at 5°C exhibited a highly irreversible character. This implies significant structural reorganization of the network during the heating stage from 5°C. Analogous temperature irreversibility has been observed in emulsion electrophoretic mobility measurements and in solution surface tension measurements of the corresponding caseinate systems at pH values near the isoelectric point of the protein.     

HEAT-INDUCED GELATION AND PROTEIN-PROTEIN INTERACTION OF ACTOMYOSIN1

Natural actomyosin (NAM) and “crude” actomyosin formed gels yielding maximum strengths (from back extrusion force) at pH 5.0 and 5.5, respectively. At pH 6.0, NAM gels had a least protein concentration endpoint (LCE) value of 6 mg/ml. Gel strength increased exponentially with an increase of NAM concentration from 3.75–10 mg/ml. With constant time (30 min)-temperature heating, NAM gel forces increased by 20.5% (NS, P>0.05) in the 30–80°C range. Arrhenius plots of NAM interaction in solution and in gelation at pH 6.0 indicated two different reaction mechanisms within the temperature zones above and below approximately 35°C for solutions and 40°C for gels. Similarity of interaction slopes above the 35–40°C region suggested one reaction mechanism for NAM molecular aggregation in solution and gelation.     

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).     

Effects of Heat-Stable Alakaline Protease Activity of Atlantic Menhaden (Brevootii tyrannus) on Surimi Gels

Heat stable protease isolated from the sarcoplasmic fraction of menhaden (Brevoorti tyrannus) muscle tissue was characterized as to optimum temperature and pH against casein substrate and its degradative action on actomyosin and surimi during heating. The optimum conditions for activity were 60°C at a pH of 7.5 to 8.0. Activity dropped off remarkably at temperatures below 45°C or above 70°C and when pH was below 7.0 or above 8.0. The enzyme(s) was capable of degrading actomyosin as observed by sodium dodecyl sulfate electrophoresis. This implicated a causative role for this protease system in the texture degradation observed during thermal processing of menhaden surimi at temperatures of 50-70°C.