Elastic Attributes of Heated Egg Protein Gels

The equilibrium stress of egg white (EW) and ovalbumin (OV) gels using the statistical theory of rubber elasticity suggested that 3.9 covalent disulfide cross-links per OV molecule were formed on gelling. DTNB and PCMB reacted with approximately 4 sulfhydryls of OV in 2% SDS and/or at 82°C. Moreover, the equivalent of 3 secondary bonds, calculated from the initial stress and presumably a composite of numerous weak secondary bonds, contributed significantly to the protein gel stress.     

Heat-induced Gelation of Chicken Gizzard Myosin

Chicken gizzard myosin solution formed a gel when heated above 40°C. The rigidity of the gel was constant above 65°C. Maximum pH for gel formation was 5.9 at 0.6M and 5.7 at 0.15M KCl. Higher rigidity of the myosin gel was observed at low ionic strength than at high ionic strength. Rigidities of myosin at 0.6M KCl increased by (mg/mL)^2.5 and at 0.15M (mg/mL)^{1, 4} myosin concentration. The strength of gizzard myosin gels was comparable to that of myosin gels from chicken breast muscle under similar conditions.     

Thermal Gelation of Brown Trout Myofibrils: Effect of Muscle Type, Heating Rate and Protein Concentration

The thermal gelation properties of myofibril solutions (KCl 0.6M; pH 6.0) from reared brown trout white and red muscles were analyzed by thermal scanning rheometry. With a heating rate of 1°C/min, red muscle myofibrils exhibited a lower gelation capacity than white muscle myofibrils at low temperatures. No difference was observed above 60°C where solid gels were formed from the two myofibril types. Increasing protein concentration or reducing heating rate increased the values of the rheological parameters at 80°C for the two muscle type myofibrils. With a low heating rate (0.25°C/min), white muscle myofibrils formed stronger gels whatever the temperature.     

Formation of two types of gels from bovine myosin

Myosin was isolated from bovine m. semimembranosus and gels were formed by heat treatment at different pH values and ionic strengths. The gels were subjected to rigidity measurements and their microstructure was studied by scanning electron microscopy. This article provides evidence that myosin can form two completely different gel structures in the pH range 5.5–6.0, depending on ionic strength. Fine stranded gel structures were formed at low ionic strength (0.25M KCl), whereas coarsely aggregated gel structures were formed at high ionic strength (0.6M KCl). The fine stranded structure had a higher rigidity than the coarsely aggregated structure. It was found that all fine strand myosin gels were formed from turbid solutions and the aggregate gels from clear solutions. When the pH was lowered to 4 in 0.6M KCl a strand-type gel structure formed spontaneously on dialysis, even without heat treatment. This structure did not change in character on heating. It was concluded that the conditions required for the formation of strand-type myosin gels were already present before the heat treatment and that the strands were made up of myosin filaments at certain pH and ionic strength combinations, which produced a turbid solution. The strand-type structures were considered specific with regard to myosin interactions which was not the case for the aggregated structures. Variation of the heating temperature in the range 55 to 65°C had no major effect on the type of structure formed.     

Effect of glucono-δ-lactone acidification and heat treatment on the physicochemical properties of silver carp mince

The physicochemical and rheological properties of silver carp mince with different levels of glucono-δ-lactone (GDL) with or without heat treatment at 90 °C for 20 min were investigated. Breaking force, deformation, and whiteness of GDL-induced gels increased with increasing GDL concentration. Heat treatment of GDL-induced gels led to a significant increase in breaking force and whiteness, but decreased deformation. Disulphide bond formation was observed in GDL-induced gels, which increased after heating of the acidified gels. Solubility profiles of gels in different solutions suggested that gel networks were mainly due to hydrophobic interactions, although other chemical interactions may also occur. SDS-PAGE showed that acidification resulted in a large decrease in myosin heavy chain (MHC) band intensity, suggesting the extensive formation of covalent cross-links among silver carp myosins during GDL-induced gelation.     

Functional Properties of Turkey Salt-Soluble Proteins

The functional properties of salt-soluble proteins (SSP) extracted from turkey breast and thigh were determined. Breast and thigh SSP extracts were comprised of similar proteins and there was no difference in the effect of pH and NaCl concentration on solubility. Gels formed in a pH 6.0, 0.5M NaCl phosphate buffer were stable to centrifugation and had the greatest rigidity. Gels formed at pH 7.0 with breast SSP were stable to centrifugation, whereas pH 7.0 thigh SSP gels were not consistently stable. Uniaxial compression was used to determine failure shear stress, failure shear strain and hardness of gels. Breast SSP at 25 mg/mL and 35 mg/mL formed gels suitable for compression analysis, whereas thigh SSP gels of similar concentration were too frail for analysis. Breast SSP had more favorable gelation properties than thigh SSP.     

Thermal gelation of globulin from Phaseolus angularis (red bean)

The heat-induced gelation properties of red bean globulin (RBG) were studied under the influence of salts and several protein structure perturbants. The viscoelastic properties of the gels were evaluated by small amplitude oscillatory tests and creep experiments. Gel structure developed progressively when a protein dispersion (≈10% w/v) was heated from 25 to 95 °C, and both the storage modulus (G′) and loss modulus (G″) increased rapidly during cooling. The addition of NaCl at lower concentrations led to increases in G′ and G″ values, with decreased creep compliance, suggesting higher viscoelasticity. At higher salt concentrations, viscoelasticity was decreased, and the optimum NaCl concentration to produce maximum gel rigidity was 0.2 M. Sodium dodecyl sulfate and urea caused more pronounced reduction of the gel moduli than dithiothreitol and N-ethylmaleimide. The data suggest that hydrophobic interactions and hydrogen bonding play an important role in heat-induced gelation, while electrostatic interactions and a balance of attractive–repulsive forces are also important. The gels formed at 95 °C exhibited a homogenous microstructure with extensive cross-links and sheet-like network structures.     

A COMPARISON OF THE VISCOELASTIC PROPERTIES OF CONVENTIONAL AND MAILLARD PROTEIN GELS

The properties of gels prepared by heating solutions of bovine serum albumin (BSA) for 30 min at 121C in the presence and absence of glucono-delta-lactone (GDL gels) and xylose (Maillard gels) were compared. During formation the pH of the Maillard and GDL gels decreased to 4.9 whereas the pH of the gels formed in the absence of GDL or xylose remained near neutral. Maillard gels show much less syneresis compared with the GDL gels and contained nondisulphide covalent crosslinks as evidenced by very low protein solubilities in mixtures of sodium dodecyl sulphate and β-mercaptoethanol. Both the GDL and Maillard gels could be formed at much lower protein concentrations than the neutral conventional gels. The stress relaxation of the gels in compression was measured and the response analyzed using Peleg's equation. The parameters in this equation were not strongly dependent on protein concentration or degree of deformation. The neutral pH gels were far more elastic than the low pH gels, but despite the difference in crosslinking mechanisms the viscoelastic behaviour of the Maillard and GDL gels was similar. However, the break strength and asymptotic residual modulus of the Maillard gels were higher. It is suggested that the stress relaxation occurs in weaker, noncovalently linked regions of the gel, whereas the nondisulphide covalent crosslinks in the Maillard gels reinforce strong regions already containing disulphide linkages.     

A Comparison Between Ovalbumin Gels Formed by Heat and by Guanidinium Hydrochloride Denaturation

Ovalbumin was denatured by heat or by addition of 6M guanidinium hydrochloride (GuHCl) at pH 2.5. Denaturation by heat led to immediate gel formation whereas denaturation by GuHCl yielded gels only after subsequent removal of the denaturant. The two types of gels formed were compared by using texture measurements. Chemically denatured molecules had the largest hydrodynamic volume and also formed the hardest gels (protein concentration: 6% w/v). This difference in gel hardness was, however, much enhanced if the denaturant was slowly removed from the protein solution. Hence, the rate of gel formation appears to be of greater consequence than the degree of protein unfolding for the hardness of the gels formed.     

Heat Gelation Properties and Protein Extractability of Beef Myofibrils

At a heating rate of 1^oC/min suspensions (pH 6.0) of isolated beef myofibrils were found to start forming gels at 43-56^oC, as detected by dynamic rheological measurements. The increase in gel storage modulus levelled off at temperatures > 65^oC. At medium to high (0.3-0.6M) concentrations of sodium chloride, addition of pyrophosphate (plus magnesium chloride) had the following effects: (1) both the protein extractability of non-heated myofibrils and the storage moduli of heat-induced gels were markedly increased; (2) the apparent activation energy for gel formation was decreased. Increasing concentrations of sodium chloride, up to 0.5-0.6M, increased the protein concentration of the liquid phase of the gels.     

ELECTROSTATIC EFFECTS ON PHYSICAL PROPERTIES OF PARTICULATE WHEY PROTEIN ISOLATE GELS

Physical properties of particulate whey protein isolate gels formed under varying electrostatic conditions were investigated using large strain rheological and microstructural techniques. The two treatment ranges evaluated were adjusting pH (5.2‐5.8) with no added NaCl and adjusting the NaCl (0.2‐0.6 M) at pH 7. Gels (10% protein w/v) were formed by heating at 80C for 30 min. The large strain properties of fracture strain (γ_f), fracture stress (σ_f), and a measure of strain hardening (R_0.3) were determined using a torsion method. Gel microstructure was evaluated using scanning electron microscopy (SEM) and gel permeability (B_gel). Overlaying σ_f and γ_f curves for pH and NaCl treatments demonstrated an overlap where gels of equal σ_f and γ_f could be formed by adjusting pH or NaCl concentration. The high fracture stress (σ_f～ 23 kPa and γ_f～ 1.86) pair conditions were pH 5.47 and 0.25 M NaCl, pH 7.0. The low fracture stress (σ_f～ 13 kPa and γ_f～ 1.90) pair conditions were pH 5.68 and 0.6 M NaCl, pH 7.0. The 0.25 M NaCl, pH 7 treatment demonstrated higher R_0.3 values than the pH 5.47 treatment. When the sulfhydryl blocker n‐ethylmaleimide was added at 2 mM to the 0.25 M NaCl, pH 7 gel treatment, its rheological behavior was NSD (p>0.05) to the pH 5.47 gel treatment, indicating disulfide bond formation regulated strain hardening. Altering surface charge or counterions, and disulfide bonding, was required to produce gels with similar large strain rheological properties. An increase in gel permeability coincided with an increase in pore size as observed by SEM, independent of rheological properties. This demonstrated that at the length scales investigated, microstructure was not linked to changes in large strain rheological properties.     

The mechanism of formation of gels from myosin molecules

Heat-set myosin gels form the basis of the adhesive that binds particles of meat together in meat products. The manner in which a gel network is formed from myosin has been investigated by studying the aggregates produced when dilute solutions of rabbit skeletal myosin molecules in 0.6 M KCI, 20 mM potassium phosphate, pH 6.5, were heated at a single temperature between 30 and 60°C. The aggregates have been examined by transmission electron microscopy after either negative staining or rotary shadowing. After heating at 30°C for 30 min. no change in structure is detected. After heating at 35°C for 30 min, the two heads of some myosin molecules coalesce and some dimers are formed by aggregation through the heads. After heating at 40°C for 30 min. up to about 13 myosin molecules aggregate through their heads to form a globular mass up to 60 nm across with the tails radiating outwards. At higher temperatures such head-linked oligomers aggregate further. At 48°C oligomers coexist with aggregates formed by the coalescence of two or more oligomers. In such aggregates the globular masses are in close proximity and tails radiate from them. After heating myosin at 50°C, aggregates are formed by the coalescence of more oligomers and the tails are seen only indistinctly. At 60°C the particles formed contain a large number of globular masses and are typically 100 to 200 nm across, occasionally up to 1 μm. It is possible that the globules making up the strands of the gel networks in scanning electron micrographs are composed of similar particles. It is suggested that these globules are formed by head-head interactions but that tail-tail interactions may be important in forming the strands and cross-links of the gel network. When a heat-set myosin gel is compacted by centrifugation, the supernate contains essentially all the LC1 and LC3 light chains of the parent molecule but only a small fraction of the LC2 light chains. We suppose that dissociation of the LC1 and LC3 chains from the heads creates hydrophobic patches which cause intramolecular and intermolecular head association.     

Formation and properties of glycinin-rich and β-conglycinin-rich soy protein isolate gels induced by microbial transglutaminase

The gelation and gel properties of glycinin-rich and β-conglycinin-rich soy protein isolates (SPIs) induced by microbial transglutaminase (MTGase) were investigated. At the same enzyme and protein substrate concentrations, the on-set of gelation of native SPI and the viscoelasticity development of correspondingly formed gels depended upon the relative ratio of glycinin to β-conglycinin. The turbidity analysis showed that the glycinin components also contributed to the increase in the turbidity of SPI solutions incubated with MTGase (at 37 °C). Textural profile analysis indicated that the glycinin components of SPIs principally contributed to the hardness, fracturability, gumminess and chewiness values of corresponding gels, while the cohesiveness and springness were mainly associated with the β-conglycinin components. The strength of MTGase-induced gels of various kinds of SPIs could be significantly improved by the thermal treatment. The protein solubility analyses of MTGase-induced gels, indicated that besides the covalent cross-links, hydrophobic and H-bondings and disulfide bonds were involved in the formation and maintenance of the glycinin-rich SPI gels, while in β-conglycinin-rich SPI case, the hydrophobic and H-bondings were the principal forces responsible for the maintenance of the gel structure. The results suggested that various kinds of SPI gels with different properties could be induced by MTGase, through controlling the glycinin to β-conglycinin ratio.     

Changes in Gelling Behavior of Whey Protein Isolate and β-Lactoglobulin During Storage: Possible Mechanism(s)

Dry-heat treatment of a dialyzed whey protein isolate at 80°C for 7 days resulted in a decrease in hardness (from 1.55N to 0.49N) of gels formed from a 12% solution. Partial denaturation and progressive polymerization of protein was observed. The monomeric β-lactoglobulin concentration of the whey decreased from 60.64% to 33.33%after 7 days at 80°C. The rate constants determined at 40 to 80°C were used to calculate an Arrhenius relationship for the polymerization. After one year at 25^oC, 18% of monomeric β-lactoglobulin was projected to be converted to higher-molecular-weight material. The polymerization apparently did not involve disulfide cross-links.     

钙离子对白鲢鱼糜热诱导凝胶化的影响

本文通过不同浓度钙离子对白鲢鱼糜凝胶的凝胶特性、溶解率及MHC影响的研究,探讨了Ca2+增强白鲢鱼糜凝胶特性的机理及在白鲢鱼糜中的适宜添加量。结果表明,低浓度的钙离子(10、20mmol/kg)可以激活内源性转谷氨酰胺酶,催化MHC之间共价交联形成ε-(γ-Glu)-Lys共价键,导致鱼糜凝胶溶解率降低,MHC减少,凝胶特性增强,且钙离子的最适添加量为20mmol/kg;但是50mmol/kg的钙离子浓度使MHC的交联受阻,致使鱼糜凝胶特性降低,溶解率增加;当钙离子浓度达到80mmol/kg时,钙离子可与鱼糜蛋白之间形成蛋白质-钙-蛋白质的钙桥结构,使凝胶变硬,弹性降低。     

Effects of CaCl<Subscript>2</Subscript> on chemical interactions and gel properties of surimi gels from two species of carps

Effects of CaCl₂ on chemical interactions, textural properties and expressible moisture content of suwari and kamaboko gels from yellowcheek carp and grass carp were investigated. And the correlations between the contents of chemical interactions and physical properties of surimi gels were analyzed. The contents of chemical interactions, especially non-disulfide covalent bonds, disulfide bonds and hydrophobic interactions of suwari and kamaboko gels, varied with addition concentration of CaCl₂ and fish species. Suwari and kamaboko gels from yellowcheek carp exhibited higher breaking force, deformation and gel strength than these from grass carp. Surimi gels (suwari and kamaboko gels) from yellowcheek carp and grass carp exhibited their maximum gel strength when 40 mmol/kg and 100 mmol/kg CaCl₂ was added, respectively. Addition of CaCl₂ at high concentration resulted in low water holding capacity of surimi gels. Correlation analysis indicated that the contents of nonspecific associations, ionic bonds, hydrophobic interactions and sulfhydryl groups exhibited significant correlation with breaking force of surimi gels from yellowcheek carp and grass carp. Additionally, the content of non-disulfide covalent bonds had significant positive correlations with breaking force and expressible moisture of surimi gel from yellowcheek carp.     

Assessment of Cross-Linking in Combined Cross-Linked Soy Protein Isolate Gels by Microbial Transglutaminase and Maillard Reaction

ABSTRACT:  Soy protein isolate (SPI) gels were produced using single cross-linking agents (SCLA) of microbial transglutaminase (MTG) via incubation for 5 or 24 h (SCLA-MTG). When powdered SCLA-MTG gels were heated for 2 h with ribose (R2) (2 g/100 mL), dark brown gels were formed, and these were designated as combined cross-linking agent (CCLA) gels: MTG5(R2) and MTG24(R2). The results showed that the levels of Maillard-derived browning and cross-links of MTG5(R2) and MTG24(R2) gels were significantly ( P  < 0.05) lower than a control gel produced without MTG (SCLA-R2) even though the percentage of ribose remaining after heating of these gels was similar, indicating that a similar amount of ribose was consumed during heating. ɛ-(γ-glutamyl)lysine bonds formed during incubation of SPI with MTG may have reduced the free amino group of SPI to take part in the Maillard reaction; nevertheless, ribose took part in the Maillard reaction and initiated the Maillard cross-linkings within the CCLA gels.     

Ionic Strength Effects on Heat-induced Gelation of Myofibrils and Myosin from Fast- and Slow-twitch Rabbit Muscles

The effects of ionic strength on myofibrils and myosin from rabbit fast-twitch Psoas major (PM) and slow-twitch Semimembranosus proprius (SMp) muscles before and after heating were studied by electron microscopy and thermal scanning rheometry. The direct suspension of proteins in low ionic strength (0.2M KCl; pH 6.0) led to very weak gels, whereas a gradual lowering of the ionic strength (by dialysis against 0.2M KCl; pH 6.0) of 0.6M KCl protein solutions induced strand-type networks at low temperature and strong heat-induced gels. As shown by transmission and scanning electron micrographs, in low ionic strength, SMp myosins formed shorter filaments before heating and thinner and shorter structures in heat-induced gels, as well as a lower gel porosity than PM myosins.     

Interactions in bovine serum albumin–calcium alginate gel systems

Young's modulus of heat-denatured gels of calcium alginate and bovine serum albumin (BSA) was determined and compared to the modulus of BSA gels containing sodium alginate and to pure BSA gels. Ionic strength, pH, and calcium concentration were varied. The BSA/Ca-alginate gels were either prepared with -glucono-δ-lactone (GDL) and CaCO₃ to induce alginate gelation before the gelation of BSA, or by soaking heat-denatured BSA/Na-alginate gels in a CaCl₂ solution. BSA/Ca-alginate gels were stronger than BSA/Na-alginate gels at all conditions, and stronger than pure BSA gels up to higher pH values and up to somewhat higher ionic strengths than BSA/Na-alginate gels. The strength of BSA/Ca-alginate gels was highly dependent on the strength of the alginate gel. This was shown by variation of the calcium concentration and by soaking the gels in EDTA, NaCl, and CaCl₂ solutions. When BSA/Na-alginate or BSA/Ca-alginate gels prepared at optimum conditions were soaked in solutions of higher ionic strength or pH, no reduction in gel strength was observed. Consequently, they were much stronger than gels that were prepared directly at high pH or ionic strength. The results may suggest that the alginate network in a BSA/Ca-alginate gel increases the effectiveness of electrostatic BSA-alginate cross-links or entanglements. However, other explanations are also possible.     

The effect of rosemary extract and omega-3 unsaturated fatty acids on the properties of gels made from the flesh of mackerel (Scomber scombrus) by high pressure and heat treatments

Gels made from the flesh of mackerel (Scomber scombrus) and fortified with rosemary extract and omega-3 unsaturated fatty acids were studied in connection with high pressure/thermal treatments. Elasticity and breaking deformation were significantly higher in pressure-induced gels (300 MPa, 25 °C, 15 min), while hardness was considerably lower. For gels without ingredients the fraction solubilised with 8 M urea and 2% β-mercaptoethanol was larger in the pressurised samples, indicating more covalent bonding in heat-induced gels which could not be disrupted by the solubilising agent. Scanning electron microscopy showed that pressure-induced gels generally presented a structure more compacted than heat-induced gels. The high pressure activated lipid oxidation, the antioxidant effect of rosemary being evident in all samples.