Properties Of Soy Protein Isolate Research Articles

Improvement of the encapsulation capacity and emulsifying properties of soy protein isolate through controlled enzymatic hydrolysis

Self-assembling nanoparticle made from soy protein hydrolysates has proved to be a promising delivery system due to its excellent biocompatibility and synthetic feasibility. In this study, the critical parameters that control the SPI hydrolysate structure and its encapsulation capacity have been assessed. Three different enzymes, including Flavorzyme, Neutrase and Alcalase, were selected to hydrolyze soy protein isolate (SPI), and a solvent evaporation method was used to fabricate β-carotene loaded nanoparticles. Microstructure observation, SDS-PAGE, surface hydrophobicity, and endogenous fluorescence analysis were carried out to examine the key structural factors influencing encapsulation efficiency of SPI hydrolysates nanoparticles (SPIHs). It was found moderate exposure of hydrophobic amino acids inside the 7 S globulin via Flavorzyme controlled hydrolysis can increase the surface hydrophobicity of SPIH, therefore improving its emulsifying properties, while excessive hydrolysis of 7 S by Alcalase would cause weak hydrophobic interactions between the hydrophobic amino acids, which restricted the binding site with β-carotene. Above results provide a foundation for fabricating nanoparticles encapsulating lipophilic compounds with high encapsulation rate from SPI hydrolysates (SPIH).

Effects of catechin types found in tea polyphenols on the structural and functional properties of soybean protein isolate–catechin covalent complexes

Soy protein isolate (SPI) has useful functional properties, such as gelation, emulsification, and foaming. However, SPI is usually dense and has a unique spherical structure, which hinders its practical application. In this study, the effects of three typical catechins (epigallocatechin gallate (EGCG), epigallocatechin (EGC), and epicatechin (EC)) on the structure and functional properties of soy protein isolate (SPI) under alkali conditions were investigated. Compared with the native SPI, the fluorescence intensity of SPI–EC, SPI–EGC, and SPI–EGCG complexes decreased, while their fluorescence quenching rate and binding sites increased, indicating the formation of covalent complexes. The SPI–EGCG complex has a higher fluorescence quenching rate and more binding sites than those of SPI–EC and SPI–EGCG complexes. The emulsifying activity and stability of the SPI–EGCG complex were 1.16 m2/g and 147 min, respectively, higher than those of latter two complexes. Hence, the functional property of SPI and the stability of catechins could be improved by the covalent interaction between the two. This study provides new insights into the relationship between the type of polyphenol and the structure of SPI.

Effect of d-galactose on physicochemical and functional properties of soy protein isolate during Maillard reaction

Maillard reaction (MR) of soy protein isolate (SPI) and d-galactose with the mass ratio (4:1, 2:1, and 1:1) was conducted. The conformation of SPI was changed from ordered to disordered and the SPI molecule was unfolded and stretched after MR. The amino acids covalently bonded to the carbonyl group of d-galactose are mainly lysine and arginine of SPI. In addition, sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated the formation of constituents with high-molecular-weight during MR. The more the d-galactose content in MR, the higher the degree of glycation and surface hydrophobicity of SPI-d-galactose conjugates. The solubility at different pH, emulsifying and foaming properties of SPI were enhanced after MR, and these properties increased with the increasing of d-galactose content in MR. d-galactose enhanced the viscosity of SPI, and changed its viscoelasticity. Meanwhile, the hydrophilic d-galactose group improved the physiological and biological properties of amphiphilic SPI, the more d-galactose content in MR, the more significant the enhancement of the properties including the fat binding capacity, bile acid binding capacity, hypoglycemic effect, antioxidant and antibacterial activity. Our work showed that d-galactose had a great influence on the structure of SPI, and further affected its functionalities.

Effect of Ionic Strength on Heat-Induced Gelation Behavior of Soy Protein Isolates with Ultrasound Treatment.

This study investigated the effect of ultrasound on gel properties of soy protein isolates (SPIs) at different salt concentrations. The results showed that ultrasound could significantly improve the gel hardness and the water holding capacity (WHC) of the salt-containing gel (p < 0.05). The gel presents a uniform and compact three-dimensional network structure. The combination of 200 mM NaCl with 20 min of ultrasound could significantly increase the gel hardness (four times) and the WHC (p < 0.05) compared with the SPI gel without treatment. With the increase in NaCl concentration, the ζ potential and surface hydrophobicity increased, and the solubility decreased. Ultrasound could improve the protein solubility, compensate for the loss of solubility caused by the addition of NaCl, and further increase the surface hydrophobicity. Ultrasound combined with NaCl allowed proteins to form aggregates of different sizes. In addition, the combined treatment increased the hydrophobic interactions and disulfide bond interactions in the gel. Overall, ultrasound could improve the thermal gel properties of SPI gels with salt addition.

A systematic study of the impact of the isoelectric precipitation process on the physical properties and protein composition of soy protein isolates

The functional properties of soy protein isolates (SPIs), which are crucial for their successful use in food applications, depend on their protein physical properties and composition. Although the production process of SPIs is well-known and established industrial practice, fundamental knowledge on how the different isolation steps and varying isolation conditions influence these properties is lacking. Here, these characteristics were systematically investigated by assessing the impacts of the various steps of a conventional isoelectric precipitation based SPI production protocol. Protein denaturation and colloidal state were evaluated with differential scanning calorimetry and dynamic light scattering combined with (ultra)centrifugation, respectively. The protein composition (on protein subunit level) was assessed via size-exclusion chromatography. Hexane defatting was found not to cause protein denaturation. Alkaline extraction at pH values between 7.0 and 9.0 resulted in no differences in protein physical properties or composition. Subsequent acid precipitation at pH 5.5 resulted in SPIs with a lower 7S/11S ratio and higher protein solubility at neutral pH than when produced at pH 4.5 and 3.5. SPIs obtained at all evaluated precipitation pH values contained a considerable amount of aggregated protein structures. Spray-drying of SPI did not result in a higher degree of protein denaturation or in a loss of protein solubility compared to freeze-drying, but a smaller amount of soluble aggregates was observed in spray-dried SPIs. Hence, alterations in the isolation procedure can result in SPIs with moderately different physical properties and protein composition, which might lead to different functional properties and thus applicabilities in certain food systems.

Comparison of the physical stabilities and oxidation of lipids and proteins in natural and polyphenol-modified soybean protein isolate-stabilized emulsions

Oil-in-water emulsions are widely used in the food industry; however, lipids are often easily oxidized, which may adversely affect food quality. Herein, we investigated the effects of alkali treatment, free radical induction, and carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS)-mediated synthetic methods on the structures and antioxidant properties of soy protein isolate (SPI)–gallic acid (GA) conjugates and the physical stabilities and protein–lipid co-oxidation properties of the resulting emulsions. These three methods are well established; however, their effects on the same protein–phenolic compound system have not been directly compared. Additionally, the co-oxidation of proteins and oils in emulsions remains unexplored. Alkali treatment yielded superior antioxidant properties compared to those obtained using free radicals or EDC/NHS, as this method was more likely to yield CS bonds and resulted in an increased quantity of grafted GA. Spectroscopic analysis showed that alkali treatment promoted GA oxidation and thereby increased GA-protein interactions and the quenching of tryptophan fluorescence. Correspondingly, EDC/NHS-mediated conjugation retained the activity of the hydroxyl groups of GA to the largest extent. Moreover, the grafting of GA improved the physical and oxidative stabilities of the emulsions. In particular, EDC/NHS-mediated conjugation produced an emulsion with optimal oxidative stability owing to its effective inhibition of lipid and protein oxidation. Conversely, the conjugates synthesized via alkali treatment and free radical induction displayed less inhibition of lipid oxidation and promoted protein oxidation. In conclusion, optimized protein–phenolic compound conjugates for use in developing nutritional fortification products with longer shelf lives can be obtained by using appropriate synthetic methods.

Gel properties of soy protein isolate-potato protein-egg white composite gel: Study on rheological properties, microstructure, and digestibility

In order to improve the nutritional and gelling properties of soy protein isolate (SPI) gel system, potato protein (PP), egg white (EW) and PP-EW mixtures were added. The texture properties, intermolecular forces, and secondary structures of the gels were examined. Then the microstructure observation, rheological measurement and digestibility assay were conducted. The results showed that the gel of 3PP-3EW had the highest proportion of β-sheet (47.04%), the most ordered gel structure, and the highest proportion of immobilized water (96.03%). The digestibility of SPI-PP-EW gels was higher than that of SPI-PP gel or SPI-EW gel. With the increase of EW proportion, the gel hardness increased along with the increased proportion of covalent bonds. This study is conducive to the development of meat analogues with better amino acid pattern.

Comparison of soy protein isolate-(–)-epigallocatechin gallate complexes prepared by mixing, chemical polymerization, and ultrasound treatment

The effects of the preparation method (mixing, chemical polymerization, or ultrasound treatment) on the structure and functional properties of soy protein isolate-(–)-epigallocatechin-3-gallate (SPI-EGCG) complexes were examined. The mixing treated SPI-EGCG samples (M−SE) were non-covalently linked, while the chemical polymerization and ultrasound treated SPI-EGCG samples (C-SE and U-SE, respectively) were bound covalently. The covalent binding of EGCG with protein improved the molecular weight and changed the structures of the SPI by decreasing the α-helix content. Moreover, U-SE samples had the lowest particle size (188.70 ± 33.40 nm), the highest zeta potential (−27.82 ± 0.53 mV), and the highest polyphenol binding rate (59.84 ± 2.34 %) compared with mixing and chemical polymerization-treated samples. Furthermore, adding EGCG enhanced the antioxidant activity of SPI and U-SE revealed the highest DPPH (84.84 ± 1.34 %) and ABTS (88.89 ± 1.23 %) values. In conclusion, the SPI-EGCG complexes prepared by ultrasound formed a more stable composite system with stronger antioxidant capacity, indicating that ultrasound technology may have potential applications in the preparation of protein-polyphenol complexes.

Selective proteolysis of β-conglycinin as a tool to increase air-water interface and foam stabilising properties of soy proteins

Proteolysis of food proteins changes their conformation and often generates bioactive peptides, leading to improved nutritional value and techno-functional properties. Protein isolates that originated from plants are generally a mixture of several proteins. Enzymatic hydrolysis of such mixtures has a drawback, as it is often unclear which proteins in the mixture are hydrolysed, leading to poorly reproducible outcomes. In the present study, we applied a controlled methodology, called selective proteolysis, and investigated its effects on the air-water interface and foam stabilising properties of soy protein isolate (SPI). We selectively hydrolysed 7S β-conglycinin of SPI, while 11S glycinin remained relatively intact. Hydrolysates were obtained at two different degrees of hydrolysis (DH). Selective hydrolysis resulted in increased surface activity, and a higher foamability, which nearly doubled. The size of the peptides seemed to significantly affect the mechanical properties of the layer at the air-water interface, which was studied by removing peptides smaller than 14 kDa via dialysis. Peptides smaller than 14 kDa were found to hinder the interfacial network formation, while peptides larger than 14 kDa increased the interfacial stiffness. This was also reflected in the foam stability, as the hydrolysate with a low DH resulted in significantly higher foam stability than the hydrolysates with higher DH. We demonstrated that the selective proteolysis of β-conglycinin can increase the soy protein interface and foam stabilising properties, which could lead to new healthy and more sustainable food products.

Micronization using combined alkaline protease hydrolysis and high-speed shearing homogenization for improving the functional properties of soy protein isolates

The present study aimed to investigate the functional properties of soybean protein isolate (SPI) treated with alkaline protease and high-speed shearing homogenization. Alkaline protease-hydrolyzed SPIs that were characterized by varying degrees of hydrolysis between 0 and 6% were treated with high-speed shearing homogenization to obtain different micro-particulate proteins. The results showed that this combined treatment could significantly reduce the particle size of SPI by markedly degrading the structure of both the 7S and 11S subunits, thereby resulting in a significantly reduced content of β-sheet and β-turn structures. The surface hydrophobicity increased considerably for samples with hydrolysis below the threshold of 2% and then declined gradually above this threshold. Furthermore, the combination of hydrolysis and homogenization significantly improved the emulsion stability of SPI hydrolysates. It also significantly improved the foaming properties of SPI. These results demonstrated that alkaline protease hydrolysis combined with high-speed shearing homogenization represents a promising approach for improving the functional and structural properties of SPI.Graphical

The structure, antioxidant and antibacterial properties of thiol-modified soy protein isolate induced by allicin

This study investigated the effect of allicin binding on the structure, antioxidant and antibacterial properties of soy protein isolate (SPI). Results showed that allicin bound to 82.6 % free thiol groups of SPI at a molar ratio of 0.5. The combination of allicin and SPI significantly affected the structure of protein. Result of circular dichroism showed that the content of α-helix decreased by 26.9 % and the content of β-sheet increased by 12.2 % over control when the molar ratio was 0.5. The result of surface hydrophobicity signified the unfolding of SPI with the action of allicin. These results implied that allicin binding might be a suitable method for the modification of SPI. Furthermore, the antibacterialand antioxidant experiments indicated that allicin-SPI conjugates not only had the capacity to inhibit the growth of Escherichia coli and Staphyloccocus aureus, but also had DPPH and ABTS radicals scavenging activities.

Structural, nutritional and antimicrobial properties of soy protein isolate and Alyssum homolocarpum seed gum films containing carrot seed and pomegranate peel extracts

Structural, nutritional and antimicrobial properties of soy protein isolate and Alyssum homolocarpum seed gum films containing carrot seed and pomegranate peel extracts

Relationship between flexibility and interfacial functional properties of soy protein isolate: succinylation modification.

In this paper, the effects of different succinic anhydride (SA) additions on the flexibility of soy protein isolate (SPI) were investigated, and changes in protein conformation and interfacial functional properties were measured. The structure-effect relationship between conformation, flexibility, and interfacial functional properties was established. SPI was bound to SA through disulfide bonds, and the zeta potential was reduced. The β-sheet content decreased, the disordered structure increased, and there were changes in tertiary structure and microstructure. The surface hydrophobicity, disulfide bond content, and solution turbidity were reduced to 5063, 1.0967 μmol g-1 , and 0.0036 μmol g-1 respectively. The best flexibility of SPI (0.3977) and interfacial functional properties were obtained when the mass ratio of SA/SPI was 15%. Correlation analysis showed a highly significant positive correlation (P < 0.01) between flexibility and emulsification and foaming properties, with correlation coefficients of 0.960 and 0.942 for flexibility with emulsifying activity and emulsion stability respectively, and 0.972 and 0.929 for flexibility with foaming capacity and foaming stability respectively. The results suggest that succinylation-induced conformational changes of SPI improved its interfacial functional properties by changing its flexibility. These results provide theoretical guidelines for the development and application of highly emulsifiable and stable soy protein products utilizing succinylation. © 2022 Society of Chemical Industry.

The effects of thermal treatment on emulsifying properties of soy protein isolates: Interfacial rheology and quantitative proteomic analysis

In this work, the interfacial rheological properties and the quantitative changes of proteins at interfacial protein layers of emulsions stabilized by soy protein isolates (SPI) and heat-treated soy protein isolates (HSPI) were investigated. The quantification results showed that the relative quantities of albumin (2S) and glycinin (11S) in SPI decreased at the oil-water interface, suggesting that they possessed lower interfacial affinities at the interface. Basic 7S globulin presented more adsorption at the oil-water interface due to the well balance of the hydrophobic and hydrophilic groups of its amino acid sequence. The HSPI (95 °C, 20 min) showed a larger apparent diffusion rate (Kdiff) and a shorter equilibrium adsorption time. The results of interfacial rheology of globulins were consistent with their interfacial quantitative changes, which demonstrated that the interfacial behavior and adsorption ability of globulin were improved by thermal treatment. In this research, the interfacial behaviors of SPI and HSPI was illustrated by their interfacial properties and quantitative results of interfacial adsorbed protein layers, would promote a profound comprehension for the interfacial behavior of the protein and the influence of thermal treatment on protein interfacial properties.

Impact of high-power sonication on yield, molecular structure, and functional properties of soy protein isolate

This study reports the influence of high-power sonication (HPS) pre-treatment on protein yield, molecular structure, and functional properties. HPS energy densities (0–720 J/mL) were applied to soybean flour and flakes prior to protein extraction at pH 8.5 for 15 or 30 min at 600C, and 5 min at room temperature. The isolates were prepared by precipitating at pH 4.5 and had >90% protein. HPS of 720 J/mL to flakes substrates extracted 80% protein without any incubation and 85% with 15 min incubation when no-sonication control showed an extraction of 71%. FTIR showed some aggregation and intrinsic fluorescence and free SH content showed pronounced effects on isolates from flour. HPS increased the surface hydrophobicity, reduced solubility, and enhanced the emulsification and foaming properties for a few treatments. Therefore, incubation duration changed structural and functional properties more prominently than did HPS in the isolates from flour than flakes.

The slow release behavior of soy protein isolate/κ-carrageenan composite hydrogel: Effect of konjac glucomannan

Composite hydrogels are known for their potential applications in drug delivery fields. Pure κ-carrageenan (KC) hydrogels have a drug burst release behavior, which greatly limit their applications. In this study, konjac glucomannan (KGM) was used to further improve the properties of soy protein isolate (SPI)/KC composite hydrogels. The results showed that the viscoelasticity of the composite hydrogels increased at KC/KGM ratio 9:1 due to the increase of hydrogen bond interaction. Excessive addition of KGM in composite hydrogels led to the increase in frequency dependence and gel network cavity as well as the decrease in gel cohesiveness. In vitro study on glucose release behavior of composite hydrogels showed that the glucose slow release behavior was enhanced by a small amount of KGM incorporation and had highly positive correlation with the gel viscoelasticity. These results suggested that KGM had the potential to enhance the properties and drug release characteristics of composite hydrogels.

Correlating structure and emulsification of soybean protein isolate: Synergism between low-pH-shifting treatment and ultrasonication improves emulsifying properties

The functional properties of a protein (particularly emulsification) are closely related to its conformation and structure. Herein, we investigated the effect of low-pH-shifting treatment (pH 7 → 2 → 7), either individually or in combination with ultrasonication (300 W, 10 min), on the structural and emulsifying properties of soy protein isolate (SPI). Compared with individual treatment, combined treatment more significantly improved the emulsifying properties of SPI by changing its spatial conformation. The two treatment methods were shown to exhibit both synergistic and sequence-dependent effects on the emulsifying properties of SPI. In addition, we analyzed correlations between the emulsification and structure using a mathematical model to directly and explicitly elucidate structure–emulsification relationships. Combined treatment alters protein structure in two ways: low-pH-shifting treatment exposes the hydrophobic groups present in the interior of the SPI, and ultrasonication breaks disulfide bonds, which increases β-sheet content, surface hydrophobicity, and sulfhydryl content. These three factors were found to be strongly positively correlated (> 0.9), and highly positively correlated with emulsifying properties (> 0.7). The SPI structure was found to affect its emulsifying properties, thereby providing a theoretical understanding of the emulsification mechanism.

Conjugation of soy protein isolate (SPI) with pectin: effects of structural modification of the grafting polysaccharide

Recently, there has been a great interest in enhancing the emulsifying properties of soy protein isolate (SPI) by Maillard reaction. As a commonly-used grafting polysaccharide, pectin has proved useful in modifying proteins. However, effects of its structural characteristics on conjugation are still not fully understood. To address this problem, we employed alkaline or/and enzymatic treatments to modify pectin and obtained three modified samples. Structural characteristics of pectin, including the molecular weight, degree of methoxylation and acetylation, and monosaccharide compositions were measured. When conjugated with SPI, pectin with lower molecular weight and less main chains induced higher conjugate yield. Fluorescence intensity and surface hydrophobicity of all conjugates markedly reduced compared to the original SPI, suggesting a more loosened protein structure after Maillard reaction. In this study, the enzymolysis pectin proved an optimum grafting polysaccharide considering the simple preparation procedures and the highest emulsifying properties of its resulting conjugates.

Protease-induced soy protein isolate (SPI) characteristics and structure evolution on the oil–water interface of emulsion

The evolution of the microstructures and properties of soy protein isolate (SPI) at the oil–water interface under the induction of protease within 0.5 h and 2.0 h were analyzed by macroscopic characterization and structural analysis. There were significant differences in average particle size, zeta potential, microstructure, FT-IR, Raman and endogenous fluorescence of emulsion samples produced by different treatment times. Visual comparison showed the relatively uniform aggregation and distribution of SPI on the interface when induced for 1.0 h and characterized by zeta potential and rheology. Moreover, in FT-IR, Raman and intrinsic fluorescence spectra, it was found that with the induction of 0.5–2.0 h, the content of the β-turn structure was highest at 1.0 h, and strong fluorescence quenching occurred, which indicated that SPI at the interface was hydrolyzed into small peptides, and aggregated at 1.0 h and then hydrolyzed. What is more, no significant change in rheological properties was observed after induction for 1.5 h and 2.0 h. The results indicated that there existed –CO– and –NH binding due to electrostatic interaction and hydrogen bonding at 1.0 h, which caused the recombination of SPI molecules at the interface. The preparation process of SPI emulsion samples and the structural changes of SPI molecules in the oil-water interface under different protease induction times were investigated. • Evolution of structure and properties of SPI at oil–water interface protease treated. • SPI at the oil–water interface undergo aggregation and recombination after 1.0 h. • Longer treatment time reduces the viscosity and viscoelasticity of SPI emulsion. • Electrostatic interaction and hydrogen cause the aggregation and recombination of SPI.

Formation of soybean protein isolate-hawthorn flavonoids non-covalent complexes: Linking the physicochemical properties and emulsifying properties

In recent years, more and more attention had been paid to the combination of proteins and flavonoids, and several flavonoids had been reported to improve the physicochemical and emulsifying properties of proteins. This study investigated the effects of ultrasonic treatment (450 W for 10 min, 20 min, and 30 min) on the physicochemical properties, antioxidant activity, and emulsifying properties of soy protein isolate (SPI) -hawthorn flavonoids (HF) non-covalent complexes. The results showed that the addition of HF to SPI and 20 min of ultrasound could reduce α-helix and random coil, increase β-sheet and β-turn, and enhance fluorescence quenching. In addition, it decreased the particle size, zeta potential, surface hydrophobicity, and turbidity to 88.43 or 95.27 nm, −28.80 mV, 1250.42, and 0.23, respectively. The protein solubility, free sulfhydryl group, antioxidant activity, emulsifying activity index, and emulsifying stability index all increased to 73.93%, 15.07 μmol/g, 71.00 or 41.91%, 9.81 m2/g, and 67.71%, respectively. Moreover, high-density small and low-flocculation droplets were formed. Therefore, the combined ultrasound treatment and addition of HF to SPI is a more effective method for protein modification compared to ultrasound treatment alone. It provides a theoretical basis for protein processing and application in the future.