Acid-induced gelation of whey protein polymers: effects of pH and calcium concentration during polymerization

Heating whey protein dispersions (90°C for 15 min) at low ionic strength and pH values far from isoelectric point (pH>6.5) induced the formation of soluble polymers. The effect of mineral environment during heating on the hydrodynamic characteristics and acid-induced gelation properties of polymers was studied. Whey protein dispersions (80 g/l) were denatured at different pH (6.5–8.5) and calcium concentrations (0–4 mm) according to a factorial design. At pH 6.5, the hydrodynamic radius of protein polymers increased with increasing calcium concentration, while the opposite trend was observed at pH 8.5. Intrinsic viscosity results suggested that heating conditions altered the shape of protein polymers. Whey protein polymers were acidified to pH 4.6 with glucono-δ-lactone and formed opaque particulate gels. The storage modulus and firmness of gels were both affected by conditions used to prepare protein polymers. As a general trend, polymers with high intrinsic viscosity produced stronger gels, suggesting a relationship between polymer shape and gel strength.Acid gelation properties of whey protein polymers makes them suitable ingredients for yoghurt applications. Using whey protein polymers to standardize protein content increased yoghurt viscosity to 813 Pa.s while using skim milk powder at same protein concentration increased yoghurt viscosity to 393 Pa.s. Water holding capacity of protein polymers in yoghurt was 19.8 ml/g compared to 7.2 ml/g for skim milk powder protein. Acid gelation properties of whey protein polymers are modulated by calcium concentration and heating pH and offers new alternatives to control the texture of fermented dairy products.     

Role of cosolutes in gelation of high-methoxy pectin. Part 1. Comparison of sugars and polyols

Mixtures of high-methoxy pectin (DE 70; 1.0 wt%; pH 3.0) with ethan-1,2-diol, glycerol, xylitol, sorbitol, glucose, fructose or sucrose at concentrations of 50, 55, 60 and 65 wt% were prepared at 95 °C and changes in storage modulus (G′) and loss modulus (G″) during cooling to 5 °C, heating to 90 °C and re-cooling to 5 °C (at 1 °C/min) were measured at 1 rad s⁻¹ and 0.5% strain. In all cases, the onset temperature for gelation during cooling and the moduli recorded at 5 °C increased with increasing concentration of cosolute. Both values, however, were substantially lower for the liquid cosolutes (ethan-1,2-diol and glycerol) than for mixtures incorporating the same concentrations of the solid cosolutes. The difference is attributed to inhibition of pectin–pectin interactions by pectin–cosolute interactions, which in turn are inhibited by cosolute–cosolute interactions, these being weaker for the liquid cosolutes than for the solids (as indicated by lower melting points). On heating, there was an initial reduction in modulus, with the same temperature-course as the increase on cooling; for the solid cosolutes, this was followed by an increase attributable to hydrophobic association of methyl ester substituents. No such increase was seen with the liquid cosolutes, but differential scanning calorimetry studies showed two (reversible) thermal transitions in all cases, one over the temperature-range of the initial gelation process on cooling and the other coincident with the increase in modulus on heating in the presence of the solid cosolutes. The absence of any detectable increase in modulus on heating with the liquid cosolutes is attributed to accumulation of cosolute around the polymer chains (i.e. pectin–cosolute interactions) promoting hydrophobic association between methyl ester groups on the same chain, or within small clusters of chains, with, therefore, no contribution to network structure. At high concentrations of the solid cosolutes, the increase in modulus on heating was followed by a decrease at higher temperature; this is attributed to excessive aggregation, and was reflected in lower moduli on subsequent re-cooling to 5 °C, in contrast to the enhancement in gel strength after heating and cooling that was observed at lower concentrations of the same cosolutes.     

Effect of polymer ratio and calcium concentration on gelation properties of gellan/gelatin mixed gels

Gelation properties of gellan/gelatin mixed solutions were studied using dynamic viscoelastic testing at eight different ratios of gellan (1.6–0.2% w/v) to gelatin (0–1.4% w/v) and seven different calcium levels (0–30 mM). The gelation temperature and gelation rate of the mixed gels were significantly affected by the ratio of gellan to gelatin as well as concentration of calcium. Addition of calcium at low levels resulted in an increase in gelation temperature and gelation rate compared to gels with no added calcium. Further increases in calcium increased the gelation temperature, but caused a decrease in gelation rate of the mixed gels. In addition, the presence of gelatin generally had a negative influence on gelation rate, especially at high proportions and when the solution had a high gelling temperature, probably by physically hindering the growth and development of gellan crosslinks. It appeared that in the presence of calcium, gellan formed the continuous gel matrix, with gelatin present as a discontinuous phase. Gellan/gelatin mixtures can form gels over a wide temperature range by varying the ratio of the two polymers as well as the calcium concentration.     

Associative and segregative interactions between gelatin and low-methoxy pectin: Part 2—co-gelation in the presence of Ca

The effect of segregative interactions with gelatin (type B; pI=4.9; 0–10 wt%) on the networks formed by low-methoxy pectin on cooling in the presence of stoichiometric Ca²⁺ at pH 3.9 has been investigated by rheological measurements under low-amplitude oscillatory shear. Samples were prepared and loaded at 85 °C, cooled (1 °C/min) to 5 °C, held for 100 min, and re-heated (1 °C/min) to 85 °C, with measurement of storage and loss moduli (G′ and G″) at 10 rad s⁻¹ and 2% strain. The final values of G′ at 5 °C for mixtures prepared at the same pH without Ca²⁺ were virtually identical to those observed for the same concentrations (0.5–10.0 wt%) of gelatin alone, consistent with the conclusion from the preceding paper that electrostatic (associative) interactions between the two polymers become significant only at pH values below 3.9. Increases in moduli on cooling in the presence of Ca²⁺ occurred in two discrete steps, the first coincident with gelation of calcium pectinate alone and the second with gelation of gelatin. Both processes were fully reversible on heating, but displaced to higher temperature (by 10 °C), as was also observed for the individual components. The magnitude of the changes occurring over the temperature range of the gelatin sol–gel and gel–sol transitions demonstrates that the gelatin component forms a continuous network; survival of gel structure after completion of gelatin melting shows that the calcium pectinate network is also continuous (i.e. that the co-gel is bicontinuous). On progressive incorporation of NaCl (to induce phase separation before, or during, pectin gelation) the second melting process, coincident with loss of calcium pectinate gel structure, was progressively abolished, indicating conversion to a gelatin-continuous network with dispersed particles of calcium pectinate. These qualitative conclusions are supported by quantitative analyses reported in the following paper.     

Characterization of gelation time and texture of gelatin and gelatin–polysaccharide mixed gels

The effects of cooling rate, holding temperature, pH and polysaccharide concentration on gelation characteristics of gelatin and gelatin–polysaccharide mixtures were investigated using a mechanical rheometer which monitored the evolution of G′ and G″. At low holding temperatures of 0 and 4 °C, elastic gelatin gels were formed whereas a higher holding temperature of 10 °C produced less elastic gels. At slow cooling rates of 1 and 2 °C/min, gelling was observed during the cooling phase in which the temperature was decreased from room temperature to the holding temperature. On the other hand, at higher cooling rates of 4 and 8 °C/min, no gelation was observed during the cooling phase. Good gelling behavior similar to that of commercial Strawberry Jell-O^® Gelatin Dessert was observed for mixtures of 1.5 and 15 g sucrose in 100 ml 0.01 M citrate buffer containing 0.0029–0.0066 g low-acyl gellan. Also, these mixed gels were stronger than Strawberry Jell-O^® Gelatin Desserts as evidenced by higher G′ and gel strength values. At a very low gellan content of 0.0029 g, increasing pH from 4.2 to 4.4 led to a decrease in the temperature at the onset of gelation, G′ at the end of cooling, holding and melting as well as an increase in gel strength. The gelation time was found to decrease to about 40 min for gelatin/sucrose dispersions in the presence of 0.0029 g gellan at pH 4.2 whereas the corresponding time at pH 4.4 was higher (79 min). In general, the gelation time of gelatin/sucrose dispersions decreased by a factor of 2 to 3 in the presence of low-acyl gellan. The addition of low-acyl gellan resulted in an increase in the gelation rate constant from 157.4 to 291 Pa. There was an optimum low-acyl gellan content for minimum gelation time, this optimum being pH dependent. Addition of guar gum also led to a decrease in gelation time to 73 min with a corresponding increase in the gelation rate constant to 211 Pa/min though these values were not sensitive to guar gum content in the range of 0.008–0.05 g. The melting temperature of gelatin/sucrose/gellan as well as gelatin/sucrose/guar mixtures did not differ significantly from that of pure gelatin or Strawberry Jell-O^® Gelatin Desserts. At pH 4.2, the melting rate constant was highest at a low-acyl gellan content of 0.0029 g whereas the rate constant was insensitive to low-acyl gellan content at pH 4.4. Addition of guar did not seem to affect the melting temperature or the melting rate constant.     

Whey protein concentrate/λ-carrageenan systems: Effect of processing parameters on the dynamics of gelation and gel properties

The thermal characteristics, dynamics of gelation and gel properties of commercial whey protein concentrate (WPC), WPC/λ-carrageenan (λ-C) mixtures (M) and WPC/λ-C spray-dried mixtures (DM) have been characterized. In a second stage, the effect of the gelling variables (T, pH, total solid content) on gelation and textural properties of DM was evaluated through a Doehlert uniform shell design.The presence of λ-C either in mixtures (M) or in DM promoted the WPC gelation at lower concentration (8%). M showed higher rates of formation and better gel properties (higher hardness, adhesiveness, springiness and cohesiveness) than DM.Nevertheless, when the effects of pH (6.0–7.0), heating temperature (75–90 °C) and total solid content (12–20 wt%) on gelation dynamics and gel properties of DM were studied, gels with a wide range of rheological and textural properties were obtained. While pH did not affect the gelation dynamics, it had some effect on rheological and textural properties. Total solid content and heating temperature were the most important variables for the dynamics of gelation (gelation rate (1/t_gel), gelation temperature (T_gel), rate constant of gel structure development (k_G), elastic modulus after cooling (G′_c) and textural parameters (hardness, springiness and cohesiveness).     

Rheological behavior of binary and ternary mixtures of polysaccharides in aqueous medium

The rheological behavior of mixtures of xanthan with different galactomannans is examined to evaluate the influence of the structure of galactomannan and that of the mixture composition on the physical properties; the larger synergy is observed for locust bean gum in the presence of xanthan. It is also shown that pH has only a slight influence on the rheology down to pH = 3.59; at lower pH, the G′ modulus decreases significantly.Then, the behavior of xanthan–methylcellulose mixtures is studied, paying particular attention to the storage modulus (G′) of the system, often equated to “gel strength”. The modulus values for direct dissolution of the two polysaccharides in 0.1 M NaCl show that xanthan and methylcellulose are incompatible. The rheological behavior observed is in agreement with DSC results which indicate that no specific interaction between the two polymers exists. However, upon increasing temperature, the modulus of methylcellulose increases substantially between 65 and 70 °C because of physical gelation and dominates the rheology of the mixtures. When temperature is decreased to 37 °C, the clear methylcellulose gel formed remains stable, still giving the main contribution to the overall rheology of the system. Finally, ternary systems are studied when xanthan is mixed with galactomannan and methylcellulose. In this case H-bonds involved in galactomannan–xanthan interaction break when temperature increases causing a decrease in rheological moduli which is then compensated by the gelation of methylcellulose giving an original large increase in moduli for the ternary systems. This can be interpreted as the presence of two independent but interpenetrating networks. The role of pH for these ternary systems is interesting: it is still dominated by methylcellulose and nearly independent of acidic pH (down to pH = 1.8).     

Rheology of galactomannan–whey protein mixed systems

The rheological behaviour of whey protein/galactomannan mixtures in aqueous solutions was studied under gelling conditions of the protein component, at neutral pH and at a pH close to the protein isoelectric point. The presence of the neutral polysaccharide had significant effects on the formation and viscoelastic behaviour of the cured gels. This effect was dependent on the structural organisation of the protein network. At pH 7 the galactomannan had a general positive effect on WPI gel formation. It is suggested that under these conditions, the protein network forms a continuous phase that accommodate the polysaccharide chains, acting as a filler of the protein network. The minimum protein concentration for gelation to occur, the gelation temperature and time all decrease in the presence of the galactomannan. Under pH conditions near the whey protein isoelectric point, different effects were observed as a result of the galactomannan addition. At low WPI concentration, the galactomannan had a detrimental influence on the protein network formation, but a negligible effect or even a positive influence on the gelation process at higher concentrations.     

Gelation mechanism of milk as influenced by temperature and pH; studied by the use of transglutaminase cross-linked casein micelles

Casein micelles in milk are colloidal particles consisting of four different caseins and calcium phosphate, each of which can be exchanged with the serum phase. The distribution of caseins and calcium between the serum and micellar phase is pH and temperature dependent. Furthermore, upon acidification casein micelles lose their colloidal stability and start to aggregate and gel. In this paper, we studied two methods of acid-induced gelation, i.e., 1) acidification of milk at temperatures of 20 to 50 degrees C and 2) decreasing the pH at 20 degrees C to just above the gelation pH and subsequently inducing gelation by increasing the temperature. These two routes are called T-pH and pH-T, respectively. The gelation kinetics and the properties of the final gels obtained are affected by the gelation route applied. The pH-T milks gel at higher pH and lower temperature and the gels formed are stronger and show less susceptibility to syneresis. By using intramicellar cross-linked casein micelles, in which release of serum caseins is prevented, we demonstrated that unheated milk serum caseins play a key role in gelation kinetics and characteristics of the final gels formed. This mechanism is presented in a model and is relevant for optimizing and controlling industrial processes in the dairy industry, such as pasteurization of acidified milk products.     

Characteristics of enzymatically-deesterified pectin gels produced in the presence of monovalent ionic salts

Pectin methylesterases (PMEs) from Valencia orange (p-PME) and Aspergillus aculeatus (f-PME) were used to produce pectin gels in the presence of 0.2 M monovalent ionic salts. At pH 5.0, pectin gels were induced following enzymatic deesterification of high methoxy pectin, with greater deesterification observed using p-PME compared to f-PME. Under these conditions, the deesterification limit of f-PME ended up with a pectin of DE 30.5–31.9 which did not gel at the PME reaction completion, while p-PME reduced the pectin's DE to 16.0–17.2, resulting in gel formation. The pectin gel induced by KCl was significantly stronger than the NaCl-induced gel, but LiCl did not induce pectin gelation. The gel strength was influenced by both DE and species of monovalent cation. The KCl-induced gels released less water than NaCl-induced gels. A synergistic effect on gel strength was observed from the pectin treated with a combination of (p + f)-PMEs, producing even more stable gels. These results indicated that the pectin gelation of our system would be enhanced both by using larger monovalent cation and by lowering the DE value, which would presumably be attributed to the different action patterns recognized for p- and f-PMEs. This pectin gelation system could provide a useful alternative to acid-sugar or calcium cross-linked gels in food and other industrial applications.     

鹰嘴豆分离蛋白的胶凝性

研究了蛋白质浓度、pH、NaCl及CaCl2对鹰嘴豆分离蛋白胶凝性的影响。pH3.0、无盐加入时,蛋白质分散液以溶液状存在;pH3.0、0.1mol/LNaCl与pH7.0、高离子强度(NaCl:0.5～1.0mol/L)条件下,蛋白质分散液表现出半溶液状性质。pH3.0、高离子强度(NaCl:0.5～1.0mol/L)与pH7.0、低离子强度(NaCl:0～0.1mol/L)条件下,蛋白质分散液以凝胶状存在。pH3.0、NaCl浓度0.5～1.0mol/L与pH7.0、NaCl浓度0～0.1mol/L时具有相似的胶凝动力学。CaCl2对蛋白质的胶凝性影响与NaCl基本相同。pH3.0时,CaCl2的浓度为0.1和0.3mol/L时的凝胶强度分别为24和26.4g;NaCl浓度为0.1、0.5、1.0mol/L时的凝胶强度分别为7.6、8.4和9.3g。     

Thermoreversible gelation of caseinate-stabilized emulsions at around body temperature

We have formulated food-grade protein-stabilized emulsions (30 vol% vegetable oil, 4 wt% sodium caseinate) which exhibit heat-induced gelation at around body temperature. Prior to emulsification, these systems have the continuous phase pH adjusted to between 6.8 and 5.3 and various concentrations of calcium chloride added. The minimum CaCl₂ content required to cause gelation on heating decreases with decreasing pH, and the gelation temperature also decreases with decreasing pH. Under certain conditions the small-deformation rheological change associated with the heat-induced gelation has been found to be reversible on back-cooling to ambient. The systems have also been studied with regards to viscometry and phase separation. Emulsion compositions associated with depletion flocculation by excess non-adsorbed protein are shown to be sensitive to both the ionic calcium content and the pH.     

Chemistry and uses of pectin — A review

Pectin is an important polysaccharide with applications in foods, Pharmaceuticals, and a number of other industries. Its importance in the food sector lies in its ability to form gel in the presence of Ca²⁺ ions or a solute at low pH. Although the exact mechanism of gel formation is not clear, significant progress has been made in this direction. Depending on the pectin, coordinate bonding with Ca²⁺ ions or hydrogen bonding and hydrophobic interactions are involved in gel formation. In low‐methoxyl pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains in close contact with each other. In high‐methoxyl pectin, the cross‐linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions between the molecules. A number of factors—pH, presence of other solutes, molecular size, degree of methoxylation, number and arrangement of side chains, and charge density on the molecule— influence the gelation of pectin. In the food industry, pectin is used in jams, jellies, frozen foods, and more recently in low‐calorie foods as a fat and/or sugar replacer. In the pharmaceutical industry, it is used to reduce blood cholesterol levels and gastrointestinal disorders. Other applications of pectin include use in edible films, paper substitute, foams and plasticizers, etc. In addition to pectolytic degradation, pectins are susceptible to heat degradation during processing, and the degradation is influenced by the nature of the ions and salts present in the system. Although present in the cell walls of most plants, apple pomace and orange peel are the two major sources of commercial pectin due to the poor gelling behavior of pectin from other sources. This paper briefly describes the structure, chemistry of gelation, interactions, and industrial applications of pectin.     

Impact of cosolvents on formation and properties of biopolymer nanoparticles formed by heat treatment of β-lactoglobulin–Pectin complexes

The purpose of this study was to determine the influence of neutral cosolvents on the formation and properties of biopolymer nanoparticles formed by thermal treatment of protein–polysaccharide electrostatic complexes. Biopolymer particles were formed by heating (85 °C, 20 min) an aqueous solution containing a globular protein (β-lactoglobulin) and an anionic polysaccharide (beet pectin) above the thermal denaturation temperature (T_m) of the protein under pH conditions where the biopolymers formed electrostatic complexes (pH 5). The impact of two neutral cosolvents (glycerol and sorbitol) on the self-association of β-lactoglobulin and on the formation of β-lactoglobulin–pectin complexes was examined as a function of solution pH (3–7) and temperature (30–95 °C). Glycerol had little impact on the pH-induced self-association or aggregation of the biopolymers, but it did increase the thermal aggregation temperature (T_a) of the protein–polysaccharide complexes, which was attributed to its ability to increase aqueous phase viscosity. Sorbitol decreased the pH where insoluble protein–polysaccharide complexes were formed, and greatly increased their T_a, which was attributed to its ability to increase T_m, alter biopolymer–biopolymer interactions, and increase aqueous phase viscosity. This study shows that neutral cosolvents can be used to modulate the properties of biopolymer nanoparticles prepared by thermal treatment of protein–polysaccharide electrostatic complexes.     

THE EFFECT OF SOME MEAT PROTEINS ON THE RHEOLOGICAL PROPERTIES OF PECTATE AND ALGINATE GELS

The viscosity of 1% sodium alginate and 1% sodium pectate solutions containing low levels of calcium chloride were investigated using cone and plate viscometers. The level of calcium required to initiate partial gelation was significantly lower for pectate compared with alginate. With increasing calcium chloride concentration the solutions became more pseudoplastic and eventually showed thixotropy.
One percent bovine serum albumin or 1% myoglobin was incorporated into the polysaccharide solutions together with sufficient calcium to cause incipient gelation in the absence of the protein. Myoglobin inhibited the formation of an alginate gel, the effect being greatest at a pH of about 6.3. Bovine serum albumin also inhibited alginate formation, the effect increasing with increasing pH. In contrast the addition of both myoglobin and bovine serum albumin caused gel formation in the presence of pectate below pH 6.0.
The results are discussed in terms of the protein/polysaccharide interactions and the polymer/ion interactions that can take place in these systems. The relevance of this work to the use of these polysaccharides as thickeners and gelling agents in canned meat products is considered.     

Caustic-induced gelation of β-lactoglobulin

The gelation kinetics of β-lactoglobulin (βLg) solutions has been determined in the alkaline regime over a wide range of protein concentrations, gelling temperatures and gelation pH (pH_gel), set using NaOH. The behaviour is compared with caustic-induced gelation of whey protein concentrate and the alkaline dissolution of heat-induced whey gels. The gelation time decreases significantly between neutral conditions and pH_gel 9, because of the activation of the free cysteine groups and displacement to the monomeric form, and between pH_gel 10 and 11, due to the base denaturation of βLg. Both transitions are associated with a significant decrease in the activation energy of gelation. At pH_gel >11.5 the gelation time is observed to increase with pH_gel, owing to destruction of interprotein crosslinks. These results are consistent with the recently reported observation that a minimum pH for the dissolution of βLg gels and aggregates exists around 11.6 [ Biomacromolecules 8 (2007) 1162]. This phenomenon has been assigned to the destruction of non-covalent interactions that would inhibit the final percolation of the gel.     

Study of the browning and gelation kinetics in a concentrated sheep milk and sucrose system

Browning and gelation kinetics of a sheep milk and sucrose model system with 70% total solids (simulating dulce de leche) and the influence of temperature and sucrose content on this process were studied. The Kubelka–Munk index and subjective heat stability tests were used to monitor nonenzymatic browning and to determine gelation time. Browning and gelation processes showed different kinetics where gelation was shown to occur much faster than browning. Both independent variables (temperature and sucrose content) had a significant influence in both processes, where temperature had the higher impact.     

Interaction of fullerene (C60) nanoparticles with humic acid and alginate coated silica surfaces: measurements, mechanisms, and environmental implications

The deposition kinetics of fullerene (C60) nanoparticles onto bare silica surfaces and surfaces precoated with humic acid and alginate are investigated over a range of monovalent (NaCI) and divalent (CaCl2) salt concentrations using a quartz crystal microbalance. Because simultaneous aggregation of the fullerene nanoparticles occurs, especially at higher electrolyte concentrations, we normalize the observed deposition rates by the corresponding favorable (transport-limited) deposition rates to obtain the attachment efficiencies, alpha. The deposition kinetics of fullerene nanoparticles onto bare silica surfaces are shown to be controlled by electrostatic interactions and van der Waals attraction, consistent with the classical particle deposition behavior where both favorable and unfavorable deposition regimes are observed. The presence of dissolved humic acid and alginate in solution leads to significantly slower deposition kinetics due to steric repulsion. Precoating the silica surfaces with humic acid and alginate exerts similar steric stabilization in the presence of NaCl. In the presence of CaCl2, the deposition kinetics of fullerene nanoparticles onto both humic acid- and alginate-coated surfaces are relatively high, even at relatively low (0.3 mM) calcium concentration. This behavior is attributed to the macromolecules undergoing complex formation with calcium ions, which reduces the charge and steric influences of the adsorbed macromolecular layers.     

Calcium Addition,pH and High Hydrostatic Pressure Effects on Soybean Protein Isolates—Part 2: Emulsifying Properties

Soybean protein isolates (SPI) represent an important source of proteins that are used to prepare oil-in-water (o/w) emulsions. The influence of an innovative treatment (high hydrostatic pressure, HHP) combined with calcium addition at different pH levels and protein concentrations on the formation and stability of o/w SPI emulsions was evaluated in this work. When applied separately, calcium addition or HHP treatment produced different effect at pHs 5.9 and 7.0. Calcium addition led to stable emulsions with decreased flocculation index (FI) at pH 5.9 and low protein concentration (5 g L^?1), whereas at pH 7.0, this effect was observed at high protein concentration (10 g L^?1). In these conditions, calcium would favor the arrival of big aggregates to interface, which would be modified and adsorbed during homogenization. Treatment with HHP decreased FI and stabilized emulsions during storage at pH 7.0 (but not at pH 5.9) when prepared from 10 g L^?1 protein dispersions. In these conditions, protein unfolding due to HHP-induced denaturation, and high ζ-potential would be responsible for emulsion improvement. Combination of calcium addition and HHP treatment impaired both formation and stabilization abilities of SPI at both pHs. Bridging flocculation was enhanced in these samples while interfacial protein concentration and percentage of adsorbed protein were increased. Thus, soybean proteins that were subjected to combined calcium addition and HHP treatment exhibited a great ability to associate each other, what can be useful to improve other functional properties such as gelation.     

Disulfide Bonds Influence the Heat-induced Gel Properties of Chicken Breast Muscle Myosin

The functions of thiol groups in the denaturation, aggregation and gelation of chicken breast muscle myosin during heating in 0.6M NaCl, 50mM sodium phosphate buffer, pH 6.5, was investigated by inhibiting disulfide (SS) bond formation using dithiothreitol (DTT). The endotherm of myosin heated in the presence or absence of DTT had similar thermal transition temperatures. Preventing SS bond formation increased the onset temperature for aggregation and gelation and decreased the elastic-like properties of the final gel matrix. Results indicated that SS bond formation was not a prerequisite for the gelation of chicken breast myosin. However, intermolecular SS bonds, especially from thiol groups on subfragment-1, contributed to gel network formation.