Soy Protein Isolate Components and Their Interactions (2025)

Electrophoretic, solubility and functional properties of commercial soy protein isolates

Journal of Agricultural and Food Chemistry, 1991

The effect of protein composition and degree of protein denaturation on the solubility, water-imbibing capacity (WIC), viscosity, and gelation capacity of commercial soy protein isolates was studied. It was found that the degree of denaturation may affect protein solubility, but very denatured proteins with high solubility were also detected. Isolates containing completely denatured proteins showed low gelation capacity. This characteristic is closely related to the relative amounts of the 75 and 11s proteins, since 6-7s subunit and basic 11s polypeptide were present in decreased concentrations in the soluble protein fraction. Isolates with a high degree of denaturation and intermediate solubility values presented the maximal WIC. Results confirmed that the apparent viscosity of soy protein dispersions is intimately related to WIC.

Partial Reduction of Soy Protein Isolate Disulfide Bonds

Journal of Agricultural and Food Chemistry, 1995

Partial reduction of disulfide bonds of soy protein isolates was followed electrophoretically. Isolates treated with Na2S03 under different conditions showed disappearance of high molecular weight aggregates. Acidic and basic 11s polypeptides and some whey proteins that remain in the isolates were also affected; reduction of the AB-11s subunit was very limited. The sulfitolysis method was also studied. The addition of a catalyst (CUI and oxygen showed a similar effect in the sulfitolysis of soy proteins with Na2S03. To achieve complete sulfitolysis, the presence of a denaturing and an oxidizing agent were needed. Mainly AB subunits of glycinin were reduced when urea was used, while mostly components other than AB-11s subunits were reduced when Na2S03 was used in the presence of Cu andor oxygen.

Gelation of Soybean Protein Isolates in Acidic Conditions. Effect of pH and Protein Concentration

Journal of Agricultural and Food Chemistry, 1995

Heat-induced gels were obtained from acidic and pH 8.0 soybean protein isolates, a t different pH values and protein concentrations. The isolates were characterized through solubility assays in different extraction media, and bidimensional SDS-PAGE, scanning electron microscopy and waterholding capacity were performed to analyze gels. Results indicate that acidic gels became more aggregated when the pH approached the PI. Gels obtained a t acidic pH were different from those obtained at pH 8.0, the latter having more interchain disulfide bonds and different protein species involved in the maintenance of the structure.

Protein Subunit Composition Effects on the Thermal Denaturation at Different Stages During the Soy Protein Isolate Processing and Gelation Profiles of Soy Protein Isolates

Journal of The American Oil Chemists Society, 2008

This study focussed on the evaluation of thermal denaturation at three different stages during soy protein isolation and the effect of subunit composition on the formation of heat-induced soy protein gels. Soy protein isolates (SPI) were prepared from 12 high protein lines, Harovinton variety and 11 derived null-lines which lacked specific glycinin (11S) and β-conglycinin (7S) protein subunits. Protein denaturation during SPI processing was monitored by differential scanning calorimetry (DSC). The results showed that hexane extraction of oil from soybean flours at 23 °C or 105 °C did cause changes in protein conformation. Rheological measurements showed that lines with different subunit compositions and 11S:7S ratio had distinctive gelation temperatures and resulted in gels with different network structures. All lines formed particulate gels at 11% protein. The 11S:7S ratio was not correlated to final stiffness, measured as the storage modulus G′, of SPI gels. Lower gelation temperatures were usually observed for 7S-rich lines. The absence of A3 and the combination of A1, A2 and A4 subunits of 11S fraction may suggest the formation of stiffer gels. A more detailed study of the frequency dependence of G′ for the various networks formed also indicated that differences in subunit composition influenced the network structures.

Characterization of β-Conglycinin and Glycinin Soy Protein Fractions from Four Selected Soybean Genotypes

Journal of Agricultural and Food Chemistry, 2001

The -conglycinin and glycinin fractions of soy protein were isolated from Macon, Ohio FG1, Enrei, and IL2 genotypes that were grown under the same environmental conditions. The soy protein fractions were evaluated to determine whether chemical composition and gel-forming properties were related. Amino acid analyses suggested that the hydrophobic residues may be the primary cause of differences in soy protein gel characteristics as the storage moduli increased with higher percentages of hydrophobic residues. Reversed-phase high-performance liquid chromatography profiles revealed variations in the composition of each fraction that corresponded to differences observed among the storage moduli. The gel-forming properties may be related to more than just protein content, such as the amount and type of amino acid in the fraction.

Isolation of a Glycinin-Rich Protein from Defatted Soybean

Journal of Food and Dairy Sciences

Defatted soybean flour was subjected to isolation procedures as follows: NaOH extraction / acid precipitation, water extraction / acid precipitation, NaOH extraction / cryoprecipitation and citric acid extraction / cryoprecipitation. NaOH extraction / cryoprecipitation and citric acid extraction / cryoprecipitation caused precipitation of one protein mainly consisting 11 S (glycinin) and 7 S (βconglycinin) respectively. In contrast, NaOH extraction / acid precipitation and water extraction / acid precipitation precipitated the two major soybean proteins as judged by PAGE and SDS-PAGE. Using differential scanning calorimetry (DSC), NaOH extraction / acid precipitation showed two thermal transition peaks at 72.8 o C and 86.4 o C, where as both NaOH extraction / cryoprecipitation and citric acid extraction / cryoprecipitation observed only one endothermic peak at 85.3 o C and minor peak at 75.3 o C, which may corresponding to 11S (glycinin) and 7 S (β-conglycinin) respectively. Second recycling of the thermal properties of all soy isolates exhibited irreversible denaturation behavior.

Effects of saccharide on the structure and antigenicity of β‑conglycinin in soybean protein isolate by glycation

Heterogeneity of soybean proteins: two-dimensional electrophoretic maps of three solubility fractions

Journal of Agricultural and Food Chemistry, 1982

Effects of Thermal Treatment of Soy Protein Isolate on the Characteristics and Structure-Function Relationship of Soluble and Insoluble Fractions

Journal of Agricultural and Food Chemistry, 1995

Aqueous dispersions (5-15% w/w) of native soy protein isolate were thermally treated at 80 and 100 "C for 30 min. At 100 "C, both 7 s and 11s proteins were totally denatured, while at 80 "C, the 7 s protein was totally denatured but the 11s protein was not, the denaturation degree of which was only partial and dependent on the extent of isolate denaturation. The different behaviors were reflected in the degree of aggregation, which in turn determined the yields and structural characteristics (denaturation degree, molecular weight distribution, superficial hydrophobicity, Mg2+ induced aggregation) of soluble and insoluble fraction obtained from treated isolates. A study was then performed on the effects of such structural changes on some functional properties (solubility, water imbibing, gelling and foaming properties) of soluble and insoluble fractions and, consequently, those of the total isolate.

Major proteins of soybean seeds. Reversible and irreversible dissociation of .beta.-conglycinin

Journal of Agricultural and Food Chemistry, 1979

Reversible and irreversible dissociations of 0-conglycinin were investigated by ultracentrifugation, disc electrophoresis, and immunodiffusion methods. The protein had a protomer conformation (7s) at high ionic strength (I > 0.5) or at acidic pH (pH <4.8) and a dimer conformation (10s) at low ionic strength (I < 0.2) in the pH region 4.8-11.0. Rapid interconversion between the protomer (trimeric structure) and the dimer (hexameric structure) was observed in the 0.2-0.5 ionic strength region. At very low ionic strength (I < 0.01), the CY subunit dissociated from the protein. The dissociation was reversible but may result in the generation of multiple molecular forms (B, to B6 conglycinins). The quaternary structures were stable at high ionic strength. Complete reversible dissociation into subunits occurred in 5 M urea (I = 0.01). Reversible dissociation into monomers (3-4s) appeared a t pH 12.0 (I = 0.5). Dissociation into polypeptides (2s) at pH 2.0 and 12.0 (I = 0.01) was also reversible. Irreversible dissociation at pH 13.0 may be attributable to alkaline degradation. Oligomeric storage proteins of legume seeds show a rather complicated reaction of association-dissociation. The ability to undergo conformational changes may have a physiological significance which relates to changes in osmotic pressure (Kretovich and Smirnova, 1960). The dissociation of the storage proteins has also been suggested to occur during seed germination to make the proteins accessible to proteinase attacks before final utilization by the seedling (Catsimpoolas et al., 1968). The dissociation of a protein into its protomers is, in most cases, reversible. Further dissociation of protomer into monomers is either reversible or irreversible depending on the properties of the protein and the condition under which the dissociation and, possibly, simultaneous unfolding of the monomers take place. On the basis of association-dissociation properties, vicilin proteins (7s globulins) from legume seeds can be divided into three types (Derbyshire et al., 1976). One type dimerizes to a 9-12s form at 0.1 ionic strength and neutral pH, the second retains a 7 s form at low ionic strength, and the third is insensitive to changes of ionic strength but associates to an 18s form (probably, a tetramer of 7s) at pH values near its isoelectric point. P-Conglycinin, a major 7s soybean globulin, belongs to the first type. y-Conglycinin from soybeans has a characteristic of the second type (Koshiyama and Fukushima, 1976). A representative of the third type is G1 protein from Phaseolus