Heat Gelation Properties of Actomyosin and Surimi Prepared from Atlantic Croaker

Comminuted mixtures of fish muscle (surimi) and salt undergo a sol-gel transformation when subjected to heat processing which is responsible for the textural characteristics of fabricated imitation shellfish meats. Upon “setting” a fish muscle sol at temperatures below those conventionally used for heat processing meat products, a fine translucent gel network is formed which imparts strength and resiliency to the subsequently cooked gel product. Increased firmness and opacity, as well as some loss in cohesiveness, were noted upon processing surimi sols at higher temperatures. The low temperature “setting” property of fish proteins necessitates rapid forming or extrusion of the product prior to the initiation of network formation to insure a firm texture in the final product.     

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.     

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.     

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.     

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.     

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.”     

Effects of Added Egg White or Whey Protein Concentrate on Thermal Transitions in Rigidity of Croaker Surimi

Rigidities of surimi [refined minced fish (MF)] sols, alone and in combination with egg white (EW) and whey protein concentrate (WPC) were measured during constant-rate heating by a nondestructive technique. Each of the protein types tested showed measureable changes due to variation of the heating rate or NaCl concentration of the sol. Rigidity and differential scanning calorimetric (DSC) thermograms for mixtures resembled composites of the individual protein source profiles, indicating that no major changes occurred in thermal gelling properties of the component proteins due to mixing. Maximum rigidity values indicated more favorable gelation of MF/WPC than MF/EW combinations.     

Gelation of Turkey Breast and Thigh Myofibrils: Changes During Isolation of Myofibrils

The relationship between functional properties of meat and myofibrils was examined for turkey breast and thigh by determining gel-forming ability of proteins at each step in a myofibril isolation procedure. Physical properties of thermally induced gels (70°C for 30 min) were determined by torsional fracture analysis. Maximum shear stress (force) was obtained after removal of water-soluble components, whereas filtration was required to achieve maximum shear strain (deformability). Shear stress increased 150% and shear strain 59%. Changes in fracture properties were similar between meat types, and therefore, not the cause of meat type-associated differences in comminuted turkey.     

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.     

Protein Concentration, pH and Ionic Strength Affect Apparent Viscosity of Actomyosin

Response surface methodology was used to compare effects of NaCl protein concentration, and pH on apparent viscosity (ζapp) of natural actomyosin from hake, pork and chicken muscle. Models for the three species had R² of 0.921, 0.915 and 0.814 (P<0.01) for chicken, pork and hake, respectively. Protein concentration and pH increased qapp, whereas higher ionic strength decreased it and had less influence. Interactions occurred between protein concentration and pH. Models did not reveal inter-species differences (P<0.05). However, analysis of variance of regression coefficients for each variable showed some differences due to pH.     

Thermal Gelation Characteristics of Myosin Subfragments

To elucidate the roles of the head and the tail portions of the molecule in the thermal gelation of myosin, the gelation characteristics of heavy meromyosin (HMM) and of light meromyosin (LMM) were investigated. The aggregation process of HMM corresponded to that of myosin alone in the temperature range above 50°C. Both the dynamic viscoelastic behavior and the aggregation process of LMM agreed fairly well with those of myosin alone in the temperature range up to 45 °C. Therefore, the first development of gel elasticity of myosin was attributable mainly to the tail portion of the molecule and the second was to its head portion.     

Rheological Changes During Slow Acid Induced Gelation of Milk by D-glucono-δ-lactone

Alteration in the rheological behavior of milk during acidification were studied. Structure formation during gelling was monitored by a small strain rheological scanner. Dynamic viscoelastic properties were monitored as a function of time and temperature. Time of onset of gelation, rate of network formation and development of the elastic component during acidification were accelerated at higher temperatures (55°C). Addition of calcium (0–40 mM) facilitated gelation. Preheating milk at 90°C for 5 min prior to acidification enhanced gelation and induced protein-protein network formation. The number or strength of elastically effective bonds between protein molecules were reduced and gels of lower firmness were obtained with preheated milk, compared to gels made from unhealed milk.     

Evaluation of Volume and Pressure Changes During Heating as Indices of Protein Gelation in Fish Pastes

A water jacketed piston device was used to monitor pressure and volume changes during heating of lean fish batters. Contrary to published results of a similar study with pork sausage batters, no correlation could be established between thermal gelation phenomena and pressure changes at constant volume. Pressure change at constant volume was nearly linear with respect to temperature change and therefore attributed solely to thermal expansion of the material.     

Rheological Changes During Gelation of High-Methoxyl Pectin/Fructose Dispersions: Effect of Temperature and Aging

Gels made with 0.5% and 1% pectin in 60% fructose, and a commercial sample exhibited macromolecular solution/weak gel behavior. Cooling the gels from 50–10°C increased storage (G') and loss moduli (G') of the gels. As the rate of cooling (10, 5.7, and 2.5°C/hr) a 1% pectin, 60% fructose, dispersion increased, the elasticity of the formed gel decreased; however, G' was not affected much by rate of cooling. During the first 24 hr, the changes in G'and G' were small. After 14 days storage at ambient temperature, G’values of gels increased substantially, while G' values increased slightly.     

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.     

Alpha-Helical Structure of Fish Actomyosin: Changes during Setting

Participation of the α-helix in setting was investigated using circular dichroism. The α-helicity of the actomyosin from eight species of fish decreased during incubation at 30°C or at 40°C. The extent and pattern of decrease differed among species. When rate of decrease was plotted vs rate of increase in strength of gel preincubated at 30°C or at 40°C, the two factors correlated closely. We propose that the unfolding of α-helix initiated setting.     

Proteolysis Affects Thermal Gelation of Squid Mantle Muscle

Thermal gelation of squid mantle muscle was studied by means of gel strength measurement and SDS-polyacrylamide gel electrophoresis. The gel strength of thermally induced squid meat gel decreased when squid meat paste was heated in two steps (35°C for 30 min followed by 90°C for 30 min). This decrease in gel strength was effectively depressed by the addition of protease inhibitors such as ethylenediaminetetraacetic acid (EDTA), phenylmethylsulfonyl fluoride (PMSF), and soybean trypsin inhibitor, indicating that me-tallo- and/or serine-proteases were mainly involved in the deterioration of squid meat gel prepared by two-step heating. SDS-PAGE analysis demonstrated that EDTA or PMSF suppressed the degradation of myosin heavy chain.     

Thermal Gelation Mechanism of Legumin from Broad Beans

The legumin formed a gel through formation of soluble aggregates and their juncture. Electron microscope studies indicated the legumin molecules associated to form strands. These strands then formed network-like structures, finally resulting in gel formation. The thickness of those strands and network constituents was irregular (8.3 to 36 nm). A presumed process of thermal legumin gelation was hypothesized. A comparison of gelation behaviors in legumin and in glycinin was also studied.     

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.