Soy Protein Dispersions Research Articles

Use of Dynamic Shear Rheology to Understand Soy Protein Dispersion Properties.

Soy flour dispersions are used as adhesives for bonding interior wood laminates, but the high viscosity of these dispersions requires low solids in the adhesive formulations; the greater water content causes excessive steam pressure during hot press manufacturing. This limits the utility of soy adhesives in replacing urea-formaldehyde adhesives; thus, understanding the cause of high soy viscosities is important. Lack of literature on aqueous soy flour dispersion rheology led to our dynamic rheology studies of these dispersions to understand high viscosity and the effect of various additives. Even at low soy solids, the elastic nature outweighs the viscous properties at low shear, although increasing the shear results in shear-thinning behavior after the yield point. At even higher shear, beyond the flow point where the storage and loss moduli cross, some of the dispersions show an additional shear thinning transition. The comparison of the rheological properties of aqueous dispersions of the soy flour and protein isolate, and another natural protein, ovalbumin from egg whites, led to a better understanding of different types of rheological behaviors. The experimental observations of two observed shear thinning events for soy are consistent with the model of dispersed particles, forming clusters that then form large scale flocculants.

Improvement of calcium sulfate-induced gelation of soy protein via incorporation of soy oil before and after thermal denaturation

Soy protein-based foods have attracted extensive attention for their potential health benefits. In this study, soy protein isolate (SPI) emulsions containing 10–70 mL/L of soy oil were primarily prepared either by adding the oil, emulsifying and heat treatment (OEH), or by heat treatment of the soy protein dispersion, addition of oil and emulsification (HOE). After adding CaSO4, the rheological properties of emulsions during gelation and the textural properties of the resulting gels were investigated and compared. The results showed that the increase in the volume fraction (Φ) of the soy oil from 10 to 70 mL/L resulted in the increase of the final elastic modulus (G′) of HOE and OEH emulsion gels from 5216.7 to 5827.3 Pa, and 4184.3–4935.3 Pa, respectively. The gel hardness and water-holding capacity gradually improved with increasing Φ. HOE gels exhibited greater performance of gelling properties than OEH gels at the same Φ. Confocal laser scanning microscopy images demonstrated that HOE gels, with smaller soy oil droplets dispersed within the networks, had more homogeneous and compact network structures than OEH gels. Reinforced emulsifying capacity of denatured SPI could enhance the protein-oil interactions and result in improvement of CaSO4-gelation of SPI.

Effects of xanthan gum on the rheological properties of soy protein dispersion

This study focused on the effects of addition of xanthan gum (XG) on the rheological properties of soy protein isolate (SPI) solution. Three types of tests (steady shear test, strain sweep test, and frequency sweep test) were performed to figure out the influences of shear rate on the viscosity of the SPI-XG hybrid system, the effects of strain variable on the storage modulus of the hybrid system, and the effects of frequency on both the storage modulus and the loss modulus of the hybrid system, respectively. SPI-XG hybrid system showed more obvious shear-thinning properties compared to pure SPI and pure XG solution. Meanwhile, it was found that the critical point of hybrid system was highly related to the XG concentration. XG can postpone the critical point strain amplitude to a higher value, and the addition of XG can enhance the strain resistance of hybrid system. The concentration of XG influenced the viscoelastic frequency dependence of the hybrid system significantly and complicatedly. After the addition of XG, the correlation between G′ and frequency changed from negative to positive. Keywords: rheological property, soy protein isolate (SPI), xanthan gum (XG), temperature, frequency independence DOI: 10.25165/j.ijabe.20181102.3253 Citation: Bi C H, Gao F, Zhu Y D, Ji F, Zhang Y L, Li D, et al. Effects of xanthan gum on the rheological properties of soy protein dispersion. Int J Agric & Biol Eng, 2018; 11(2): 208–213.

Stable and pH-sensitive protein nanogels made by self-assembly of heat denatured soy protein.

In this study, we examined the possibility of preparing stable soy protein nanogels by simply heating homogeneous soy protein dispersion. The protein nanogels formed were characterized by z-average hydrodynamic diameter, polydispersity index, turbidity, ζ-potential, morphology, and their stability to pH and ionic strength change. Soy protein dispersion (1% w/v) was homogeneous around pH 5.9 where it had the lowest polydispersity index (∼0.1). Stable and spherical nanogels were formed by heating soy protein dispersion at pH 5.9 under 95 °C. They sustained constantly low polydispersity index (∼0.1) in the investigated pH range of 6.06-7.0 and 2.6-3.0. The nanogels were pH-sensitive and would swell with pH change. They were stable at 0-200 mM NaCl concentration. Denaturation of soy glycinin was the prerequisite for the formation of stable nanogels. Soy protein nanogels had a core-shell structure with basic polypeptides and β subunits interacting together as the hydrophobic core; and acid polypeptides, α', and α subunits locating outside the core as hydrophilic shell. The inner structure of soy protein nanogels was mainly stabilized by disulfide bonds cross-linked network and hydrophobic interaction. Soy protein nanogels made in this study would be useful as functional ingredients in biotechnological, pharmaceutical, and food industries.

Characterization of Soy Protein Nanoparticles Prepared by High Shear Microfluidization

Soy protein nanoparticles were produced with a microfluidizer and characterized in terms of particle size, size distribution, morphology, rheological properties, and aggregate structure. Three stages of structure breakdown were observed when the soy protein dispersion was passed through the microfluidizer. A sudden change in the aggregate size was observed after a certain number of passes through the microfluidizer; such change was both concentration and pH dependent. Rheological measurements of these soy protein emulsions showed that both viscosity and storage/loss modulus decreased as the aggregate size of soy protein was decreased, indicating reduced interactions between the aggregates. The fractal dimension of the soy protein aggregates was estimated from the properties of a continuous matrix embedded with the aggregates.

Strengthening soy protein hydrogels filled with protein-coated montmorillonite nanoclay by glutaraldehyde crosslinking

To strengthen interactions in bio-nanocomposite systems, montmorillonite (MMT) was intercalated by surface-coating with soy protein before being incorporated within soy protein dispersions for cross-linking by glutaraldehyde (GA). Dynamic small strain tests were utilized as a non-destructive method to reveal the improvement of network structure in the bio-nanocomposite system. The storage modulus (G′) and loss modulus (G″) gradually increased with increasing GA concentration during isothermal treatment at 23, 60 and 90 °C. The incorporation of intercalated MMT resulted in an order of magnitude increase in the moduli. The moduli were higher at pH 5.5 than those at pH 6.5 and 10.0. At a GA concentration equal to 10 g/100 g mass of soy protein, G′ and G″ in the absence of MMT increased with an increase in temperature, while those in the presence of intercalated MMT showed the opposite trend due to restructuring of aggregated MMT. The present results confirmed that the mechanical strength of bio-nanocomposite systems can be significantly improved by first intercalating MMT with protein and subsequently cross-linking with the continuous phase protein molecules. The established chemical cross-linking method and conditions can be beneficial for preparing bio-nanocomposite materials with enhanced mechanical properties.

Transglutaminase cross-linking to enhance elastic properties of soy protein hydrogels with intercalated montmorillonite nanoclay

To strengthen the network of bio-nanocomposite hydrogels, layered montmorillonite (MMT) nanoclay was intercalated by surface-coating with soy protein (SP) before mixing with 6% w/v SP for cross-linking by microbial transglutaminase (mTGase). Dynamic rheology was performed to study variables of NaCl and mTGase concentrations, with and without 1% w/v MMT. Without mTGase, the highest storage modulus (G′) was observed at 100mM for samples without MMT, which was twice of the highest G′ for samples with MMT, at 200mM NaCl. With mTGase, a shorter gelation time and a stronger hydrogel were observed at a higher enzyme level. Overall, the non-gelling 6% w/v SP dispersion was transformed to a hydrogel with G′ of 1099Pa after addition of 100mM NaCl and 1% SP-coated MMT and treatments by 6.25U/g-protein mTGase for 2h and heating/cooling steps. The integration of surface-coating and mTGase cross-linking is promising to improve properties of the nanocomposite system.

Effects of Gum Arabic Concentration and Soy Proteins on the Flow and Viscoelasticity of their Dispersion

The present study analyzed the flow and viscoelasticity behavior of dispersions of 15 to 45% (w/v) gum arabic, 1 to 8% (w/v) soy proteins, and of gum arabic/soy proteins mixtures. Flow of gum arabic dispersions showed Newtonian behavior, while soy protein dispersions and gum arabic/soy proteins mixtures presented non-Newtonian behavior (n < 1) of shear thinning type. Viscosity increased by 239% in the gum arabic/soy protein mixture (45/8%) compared with gum arabic/soy proteins dispersions (45/0%). The consistency coefficient (K) increased with rising gum arabic or soy proteins concentration in the dispersions. The viscoelastic behavior of mixtures with low gum arabic concentrations showed G′ > G″ values (1712% in gum arabic/soy protein [15/1%] dispersions), behaving as predominantly elastic systems (viscoelastic solids). However, at higher gum arabic concentrations (35 and 45%), the gum arabic/soy protein mixtures presented G′ < G″ values (389% for [45/8%] gum arabic/soy protein), behaving as viscose dispersions (viscoelastic liquids); this shows an antagonistic effect as gum arabic and soy protein concentrations increase, which is more evident in the rheological behavior of the studied mixtures. The interaction between polysaccharides and proteins leads to a better understanding of the rheological behavior of complex mixtures, at high concentrations, allowing these model systems to be useful in the future applications in the food industry.

Effect of heat treatment on the properties of soy protein‐stabilised emulsions

SummaryThe effect of heat treatment on the properties of soy protein‐stabilised emulsions was investigated. Emulsions were prepared with unheated and heat‐treated soy protein (NSP and HSP) dispersions. Heating on soy protein dispersions at 95 °C for 30 min resulted in smaller average oil droplet size, lower tendency for oil droplet flocculation, higher protein adsorption and lower viscosity. The properties of emulsions were significantly influenced by the protein concentration. The sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE) profiles showed that the heat treatment on soy protein dispersions increased the protein adsorption at O/W interface. The viscosity of all samples at low shear rate was inversely proportional to the d32, suggesting a positive relation to the total interfacial area per unit volume. Emulsions showed shear‐thinning behaviour. The relaxation time was found to increase with aqueous phase viscosity determined by the Cross viscosity model.

Physical–chemical comparison of cow's milk proteins versus soy proteins in their calcium-binding capacities

In this study, calcium–protein interactions were thermodynamically characterized in cow's milk and in (Non-Hydrolysed, NH, or Hydrolysed, H) soy protein dispersions using Isothermal Titration Calorimetry (ITC). Both systems were compared in order to determine the efficiency of soy proteins as a possible vector for further calcium (Ca) supplementation. Regardless of the system (milk, Non-Hydrolysed and Hydrolysed-soy proteins), the thermodynamic signal from Ca–protein interactions was endothermic in nature, and was fitted by a one set of sites model. Whatever the system, μ E variations were clearly indicative of Ca–protein interactions of an electrostatic nature. Hence, the exothermic part of the signal due to electrostatic interactions was completely hidden by a strong endothermic signal. Not the Coulomb interactions but instead water molecule release, either from the hydration shells of the calcium ion and/or dehydration of the hydrophobic core of the proteins may be the driving energy source for the Ca binding onto milk or soy proteins. The nature of the Ca–protein interaction was similar in all three systems. Furthermore, as compared to milk protein, containing less Ca bound to the protein, the NH-soy protein system could be a possible protein vector for further Ca supplementation.

Effect of Dynamic High Pressure Homogenization on the Aggregation State of Soy Protein

Although soy proteins are often employed as functional ingredients in oil-water emulsions, very little is known about the aggregation state of the proteins in solution and whether any changes occur to soy protein dispersions during homogenization. The effect of dynamic high pressure homogenization on the aggregation state of the proteins was investigated using microdifferential scanning calorimetry and high performance size exclusion chromatography coupled with multiangle laser light scattering. Soy protein isolates as well as glycinin and beta-conglycinin fractions were prepared from defatted soy flakes and redispersed in 50 mM sodium phosphate buffer at pH 7.4. The dispersions were then subjected to homogenization at two different pressures, 26 and 65 MPa. The results demonstrated that dynamic high pressure homogenization causes changes in the supramolecular structure of the soy proteins. Both beta-conglycinin and glycinin samples had an increased temperature of denaturation after homogenization. The chromatographic elution profile showed a reduction in the aggregate concentration with homogenization pressure for beta-conglycinin and an increase in the size of the soluble aggregates for glycinin and soy protein isolate.

The evaluation of proteases as coagulants for soy protein dispersions

The ability of different proteases to induce the gelation of soy protein isolate dispersions (5.33% w/w) was studied. The coagulation time and gel firmness were determined using dynamic viscoelastic measurements. Among the six protease tested, papain was the most effective coagulant in terms of gel strength and coagulation speed; the second was alcalase. Degree of hydrolysis (DH), pH and viscosity profiles of soy proteins were tested during the coagulation with different proteases. The result suggested that strong interactions, other than electrostatic interaction, existed between peptides in papain and alcalase induced coagulation. Thermal and pH stability tests indicated that papain was more stable than alcalase in the temperature (60–90 °C) and pH (5.8–7.0) ranges studied. Higher papain dosages within the range of 5–13.3 U/ml resulted in firmer soy protein gels, but concentrations higher than 13.3 U/ml produced weaker gels. With the addition of 0.625 mM cysteine, the soy protein coagulation ability of papain was improved. A soy protein gel formed with 0.025% papain in the presence of 0.625 mM cysteine had about the same strength as that induced by 0.133% papain without cysteine.

Soybean Protein Dispersions at Acid pH. Thermal and Rheological Properties

ABSTRACTThe influence of pH, protein concentration, and ionic strength, on rheological properties of thermally treated acidic soy protein dispersions, was studied. Structural changes due to pH effect and thermal treatment were analized. DSC‐thermograms at pH 3.5 showed a shoulder at 74.11±0.16°C that could be attributed to both β‐conglycinin and the hexameric form of glycinin; and a peak at 81.88±0.29°C corresponding to 11S dodecameric form. At pH 2.75 one endotherm corresponded to denaturation of β‐conglycinin. The acidic dispersions presented pseudoplastic behavior withapp values higher than those at pH 8.0. At pH 3.50 the ±app was higher than at pH 2.75.The maximum viscoelasticiy was obtained with addition of 0.1 and 0.25M NaCl in the dispersions of pH 3.50 and 2.75, respectively. The increase in viscoelasticity was enhanced by the formation of 11S native fraction dimers.

Optical analysis of glucono-δ-lactone induced soy protein gelation

A new method for the investigation of the gelation behavior of soy proteins is proposed. Soy protein isolate was used to prepare a soy protein solution and glucono-δ-lactone was used as a coagulant. L ∗, a ∗ and b ∗ values of the CIE 1976 (L ∗a ∗b ∗) system were continuously monitored with a colorimeter. The stability of this system was confirmed with 13 replicates of control soy protein dispersion. Nine replicates of soy protein solution with coagulant under the same conditions were carried out to estimate the observation error. It may be possible to use L ∗, a ∗ and b ∗ values as a reliable measure of the change within the aggregation/gelation process due to the large change with a small variability given by L ∗, a ∗ and b ∗ values. Changes in structure during each step of the process were revealed by Scanning Electron Microscopy and were consistent with the results from the surface color measurements.

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Network formation and viscoelastic properties of commercial soy protein dispersions: effect of heat treatment, pH and calcium ions

Heat treatments, varying levels of protein, ionic strength and pH, in addition to the molecular interactions among food processing, which affect certain physico-chemical properties in resulting gels of commercial soy isolates (> 90% protein) are discussed. Calorimetric measurements were used to describe a partially denatured molecular order and conclude that temperature and the heating rate of temperature are expected to correlate strongly to the macromolecular conformational changes. Structural characterisation with small deformation rheological measurements (elastic modulus, tan δ, creep/compliance) was performed for a series of soy protein with the temperature treatments ranging from 30 to 90°C, in an attempt to examine the mechanisms involved. Aggregate gels were observed at lower temperatures (up to 60 ° C preheat treatment) with maximum network rigidity, which is associated with the different degrees of ‘pregelation’ stages during the production process. ‘Disaggregation’ at higher temperatures treatments weakened the molecular association and produced more elastic, fine-stranded gels. Essentially, disulphide linkages on heated networks and mainly non-covalent physical forces of attraction in their cooled counterparts, contributed to the nature of gels' behaviour, while the involvement of hydrophobic interaction was negligible. Lower concentrations were more sensitive to temperature factor. Similar conclusions on the structure and rigidity were also observed from long-time creep experiments. Both covalent and non-covalent topological interactions, which are involved in the heated (90 °C) network stabilisation, contributed proportionally with concentration to the viscoelastic constants from a six-element mechanical model. Heated protein aqueous preparations with urea, a structure perturbing agent, produced entropically elastic networks, with substantial homogeneity, but still significant enthalpic contribution was observed. Textural changes due to sensitivity on ionic strength and pH were investigated for different soy protein concentrations, using texture analysis compression measurements. The presence of salt strengthened the interaggregate forces, promoted aggregation and, therefore, stabilised the structure of partially denatured soy protein gels.

Thermorheological studies of food polymer dispersions

Reversible thermal gelation of methylcellulose (MC) was characterized by measuring the dynamic shear storage modulus (G′) as temperature was increased from 20 to 67° C at scanning rates of 1·0, 0·50 and 0·25 C°/min, and then decreased in a similar manner. The thermally induced gelation of 15·0% dispersions of soy or canola protein and meat emulsion systems with and without canola protein were also studied by measuring G′ as temperature was raised from 20 to 90°C and then lowered at a rate of 2·0C°/min. The storage modulus for solutions of MC decreased from 20 to 40°C. From 40–67°C, log G′ decreased in three stages, first slowly with temperature, then suddenly increasing three orders of magnitude between 54 and 62°C, with only small increases above 62°C. When cooled, G′ for the sample decreased in three similar stages, giving almost the mirror image of the gelation behavior. When heated from room temperature, soy and canola protein dispersions exhibited different viscoelastic behavior. G′ for the canola dispersion decreased slightly more than one order of magnitude when heated to 60°C, while the soy dispersion showed only a slight decrease in G′. At 60–90°C, structure formation in the canola dispersion was detected as G′ increased two orders of magnitude. Structure development for the soy dispersion commenced at about 78°C with G′ increasing only 10-fold. Both proteins exhibited similar increased rigidity throughout cooling. The meat emulsion containing canola experienced structural changes on heating and cooling intermediate to that of isolated canola dispersions and all-meat emulsions. The all-meat protein emulsion showed greater rigidity overall and achieved maximum structure development at a lower temperature than the canola-substituted emulsion. Thermorheological scanning provided a convenient method to explore the mechanisms involved in structure formation in these polysaccharide and protein gelling food systems.

Thermo-Rheological Changes in Protein-Replaced Meat Emulsions

Thermo-rheological profiles of a meat emulsion and dispersions of canola or soy protein isolate demonstrated that development of elasticity of the meat emulsion during heating was essentially complete at 75–80°C, whereas elasticity of canola or soy protein dispersions continued to rise with heating to 95°C. A meat emulsion containing canola protein displayed characteristics of the all-meat emulsion and canola protein dispersion thermoprofiles, but the increased structure formation from canola protein at higher temperatures did not fully compensate for an initial decrease in elasticity that resulted from the loss of meat protein.

Water‐Imbibing Capacity and Rheological Properties of Isolated Soy Proteins

ABSTRACTWater‐imbibing capacity (WIC) of isolated soy protein and rheological properties of the protein slurries from different stages of maturity were examined. WIC of isolated soy protein decreased with increasing maturity; this decrease correlated with the increase in the ratio of 7S to 11S protein. Storage time (0–6 months) had little effect on WIC of protein isolates. Consistency coefficient and flow behavior index of isolated soy protein dispersions varied with maturity; consistency coefficient decreased while flow behavior index increased with maturation. The isolated soy protein from immature soybeans formed a more viscous dispersion and showed more pseudoplasticity than that from mature soybeans. The WIC and rheological properties of isolated soy proteins at three maturation stages were related to the water ratio (Total/Imbibed) of their dispersions. A higher water‐imbibing capacity resulted in lower water ratio with higher viscosity and more pseudo‐plasticity.

Ultrasonic-induced modification of flow properties of soy protein dispersion.

The heat-treated acid precipitated proteins (H-APP), as intermediates in the commercial, production of isolated proteins from defatted soybeans, were dispersed under an ultrasonic power field over a protein concentration range from 5.4 to 12.6%. The ultrasonically untreated H-APP dispersions showed a pseudoplastic flow behavior, which was characterized by shear rate thinning, giving a yield value above 9.0%. With prolongation of the ultrasonic exposure duration, a rapid decrease in the apparent viscosity of resultant dispersions was observed under the condition of 200W/100g, with a rapid increase in flow behavior index according to the power law. In addition, ultrasonication induced the rise in critical concentration for the yield value up to 12.6%. As a result, the flow of 120 sec-irradiated dispersions became almost Newtonian at a concentration of 5.4-9.0%, but remained pseudoplastic above this range. The result obtained from gel filtration revealed that these changes in flow properties are derived from a dissociation of the protein aggregates which have formed through heat treatment of the APP prior to ultrasonication. Furthermore, the ultrasonic-induced structural alteration was considered to be associated with a partial cleavage of intermolecular hydrophobic interactions rather than with peptide-, or disulfide-bonds. Mechanical treatment such as ultrasonication is considered to be practically applicable in the production of soy protein foods, providing a significant improvement in the efficiency of unit processes such as pumping, piping, and spray drying, due to its ability to modify the flow properties of protein dispersions.