Stability Of Soy Protein Isolate Research Articles

Characterization of HIPEs stabilized by soy protein isolate with excellent rheological properties for 3D printing: Bridging the correlation among structure, function and application

Currently, the correlation between how protein structural changes affected the function of high internal phase emulsions (HIPEs) and the regulation of 3D printing performance was still unclear. Herein, this study was aimed to research the relationship between interface properties and stability of soy protein isolate (SPI) at different degrees of oxidation and prepare HIPEs with desirable rheological properties and a solid-like structure to use for 3D printing. The findings of this study suggested that moderate oxidation led to the disruption of the protein's main chain skeleton, resulting in enhancing protein flexibility and surface hydrophobicity. The HIPEs stabilized by this condition owned higher apparent viscosity, over 70% of thixotropic recovery rate, sufficient yield stress (160.8 Pa) and higher G′ and G″. This HIPEs with excellent properties could be the food-grade 3D printing inks to produce samples with high resolution. In addition, this HIPEs exhibited a slow-release effect on free fatty acids (FFA) in the gastrointestinal digestion. Finally, the findings of the correlation analysis indicated that the flexibility and surface hydrophobicity of SPI was a key factor to affect the quality of HIPEs and 3D printing. In conclusion, moderate oxidation could change the structure and interfacial characteristics of SPI, thus endowing HIPEs stabilized by modified SPI with better properties and expanding the field of SPI in the food industry. These findings not only were of great significance for guiding protein production and providing new protein-based 3D printable materials, but also this provided new possibilities for preparing fat substitutes with good appearance.

Investigating Texture and Freeze-Thaw Stability of Cold-Set Gel Prepared by Soy Protein Isolate and Carrageenan Compounding.

In this study, the purpose was to investigate the effects with different concentrations of carrageenan (CG, 0-0.30%) on the gel properties and freeze-thaw stability of soy protein isolate (SPI, 8%) cold-set gels. LF-NMR, MRI, and rheology revealed that CG promoted the formation of SPI-CG cold-set gel dense three-dimensional network structures and increased gel network cross-linking sites. As visually demonstrated by microstructure observations, CG contributed to the formation of stable SPI-CG cold-set gels with uniform and compact network structures. The dense gel network formation was caused when the proportion of disulfide bonds in the intermolecular interaction of SPI-CG cold-set gels increased, and the particle size and zeta potential of SPI-CG aggregates increased. SG20 (0.20% CG) had the densest gel network in all samples. It effectively hindered the migration and flow of water, which decreased the damage of freezing to the gel network. Therefore, SG20 exhibited excellent gel strength, water holding capacity, freeze-thaw stability, and steaming stability. This was beneficial for the gel having a good quality after freeze-thaw, which provided a valuable reference for the development of freeze-thaw-resistant SPI cold-set gel products.

Improving the Storage Stability of Soy Protein Isolate through Annealing.

This study investigated the effect of annealing treatment on the stability of soy protein isolate (SPI) during storage. Different SPI samples with varying denaturation levels were subjected to varying annealing temperatures and durations before being stored at 37 °C for 12 weeks to assess their stability. Our findings revealed that annealing at 65 °C for 30 min significantly mitigated protein deterioration, improving the stability of highly denatured proteins during storage. Surface hydrophobicity and endogenous fluorescence analyses indicated that this annealing condition induced protein structure unfolding, an initial increase in SPI hydrophobicity, and a blue shift in the maximum absorption wavelength (λmax). The slowest increase in hydrophobicity occurred during storage, along with a red shift in the maximum absorption wavelength by the 12th week. These results suggest that annealing treatment holds promise for mitigating the issue of reduced SPI stability during storage.

Modulation of physicochemical properties of lipid droplets using soy protein isolate and lactoferrin interfacial coatings.

In order to improve the physicochemical stability of soy protein isolate (SPI) emulsion, lactoferrin (LF) was used to modify the interface layer. The stable multilayer emulsion can be formed when the content of lactoferrin is 0.5% at pH 5. The emulsion with good stability was at pH 3-7, and it was also stable to temperature change. The FFAs release of SPI emulsion and LF-SPI emulsion was 103.9% and 103.7%, respectively. The results showed that the lactoferrin layer did not hinder the digestion of oil and the bioaccessibility of carotenoids, but lactoferrin layer improved the physicochemical stability of SPI emulsions. This work provides information valuable in the design of emulsion formulations for applications in the food, pharmaceutical, and personal care industries.

Influence mechanism of wheat bran cellulose and cellulose nanocrystals on the storage stability of soy protein isolate films: Conformation modification and molecular interaction perspective

This study aims to elucidate the changes and corresponding mechanisms of storage stability of soy protein isolate (SPI) films strengthened via wheat bran cellulose (WBC) and cellulose nanocrystals (CNC). The incorporation of WBC and CNC improved the mechanical strength, water resistance, water vapor and visible light barrier abilities of stored SPI-based films to varying degrees. Higher crystallinity and lower water mobility were observed in the composite films. WBC molecules reduced the irregular pores and cracks within the internal structure of the film through physical filling and non-covalent interactions, involving hydrogen bond and van der Waals force. In contrast, uniformly distributed CNC cross-linked with amino acid residues at specific binding sites under non-covalent forces. Furthermore, CNC induced the secondary conformation of proteins to transform from α-helix to β-sheet and enhanced the hydrophobic interaction, which promoted the establishment of a stable network structure and thus extended the storage stability of SPI-based films.

Preparation and characterization of soybean Protein isolate/chitosan/sodium alginate ternary complex coacervate phase

To improve morphological structure and stability of soy protein isolate - chitosan coacervate, a soy protein isolate-chitosan-sodium alginate ternary complex coacervate phase was successfully constructed by adding sodium alginate. The ζ -potential and turbidity data showed that soy protein isolate, sodium alginate, and chitosan interacted with each other in the pH range 5.0–7.0. The highest ternary coacervate yield was obtained at soy protein isolate/sodium alginate ratio 12:1 (g/g), soy protein isolate/sodium alginate:chitosan ratio 4:1 (g/g), pH 6.5, and total biopolymer concentration of 5 g/L. The viscoelastic properties and microstructure were also studied using rheology, fourier transform infrared spectroscopy, texture profile analysis, and scanning electron microscopy, which indicated that the ternary coacervates prepared in pH 5.5, 6.0, and 6.5 had a viscoelastic solid behavior (storage moduli between 12,600 and 35,000 Pa; loss moduli between 3440 and 10,000 Pa) with honeycomb porous network structures. The ternary coacervate prepared at pH 6.5 was more compact and clearly porous. The stability of the ternary complex coacervate phase to pH and ionic strength slight increased. The in situ cross-linking of sodium alginate can improve the structure properties of ternary coacervates, which may provide a new carrier to incoporate bioactive ingredients into food products.

Effect of Ultrasonic Treatment on Freeze-thaw Stability of Soy Protein Isolate Gel.

This study investigated the impact of ultrasonic modification at various ultrasonic power extents on the freeze-thaw stability of soy protein isolate (SPI) gel. The freeze-thaw stability of the gel was evaluated by examining the changes in texture, water holding capacity, microstructure and soluble protein content during the process of 5 freeze-thaw cycles. In addition, effects on particle size, surface hydrophobicity and structure were also explored. The results showed that within a certain range, the average particle size of the protein gradually decreased, and the particle size distribution was narrower with ultrasonic intensity, it may be due to the high shear and cavitation effects of sonication that reduce the degree of protein aggregation. Furthermore, we also detected that treated proteins had lower fluorescence intensity, higher surface hydrophobicity and more flexible molecular structure with the reduction of α-helical structure as well as the rise of random coil. In terms of gel freeze-thaw stability, moderate ultrasound treatment made the water holding capacity and soluble protein content of SPI gel reduce by 38.27% and 3.58%, whereas the hardness and elasticity increased by 510.23g and 0.06mm after 5 FTC. The corresponding changes of indexes of the control group were 75.05%, 51%, 1062.75g and 0.11mm, respectively. It can be observed that the change range of treated SPI gel properties was smaller than that of natural SPI gel, indicating that ultrasonic treatment can remarkably improve the freeze-thaw stability of the gel which might have something to do with changes of protein structure.

Effect of electrochemical modification on the structural characteristics and emulsion storage stability of soy protein isolate

Abstract This study investigated the impact of electrolysis modification on the structural characteristics of SPI and used the prepared novel emulsifier to improve the storage stability of the oil-in-water emulsion. The exposed sulfhydryl group content increased from 12.62 × 10−5 mol/g in the control to 14.35 × 10−5 mol/g in the SPI following electrolysis for 120 min. In addition, after electrolysis the secondary structural analysis using Fourier transform infrared spectroscopy (FTIR) indicated that samples showed a decrease in the α-helix proportion, and fluorescence spectra revealed tertiary conformational changes of the SPI. The particle size distributions of the electrolysis-treated protein solutions had monomodal distributions, and the ζ-potential absolute values became larger. The water holding capacity (WHC) and fat holding capacity (FHC) were significantly improved. The peroxide value (POV) of oil in the electrolysis-treated SPI emulsion was 14.59 mmol/kg oil, and the protein carbonyl content was also lower than that in the native protein emulsion after it was stored at 25 °C for 4 weeks. In summary, this study might suggest that an electrochemical reactor could be applied to modify the structural characteristics and functions of proteins in order to obtain the desired products.

Modification of soy protein isolate by glutaminase for nanocomplexation with curcumin

Soy protein isolate (SPI) was first treated with glutaminase to yield modified SPI (E-SPI) before its complexation with curcumin. Comparisons were made between SPI and E-SPI concerning their characteristics and effectiveness in complexing with curcumin, along with changes in physicochemical properties, 2,2-diphenyl-1-picryhydrazyl (DPPH)-scavenging capacity and storage stability of curcumin upon complexation. The action of glutaminase did not markedly change SPI structure, but modified some secondary structures, causing greater protein unfolding with more hydrophobic clusters and amino acids exposed. Glutaminase treatment increased DPPH-scavenging capacity, foaming capacity and stability of SPI. The protein concentration played a role in the changes induced by glutaminase treatment and complexation with curcumin, and 1% protein seemed beneficial (highest DPPH scavenging activity; highest loading amount 10.07%; 98% and >90% curcumin retained in 1%-E-SPI at 4 °C for 2 h and 12 h, respectively). Therefore, glutaminase treatment of SPI before complexation with curcumin appeared to be appropriate.

Improving the freeze-thaw stability of soy protein emulsions via combing limited hydrolysis and Maillard-induced glycation

The investigation of limited hydrolysis combined with Maillard-induced glycation on improving the freeze-thaw stability of soy protein isolate (SPI) was carried out. Soy protein isolate hydrolysate (SPH) was first prepared by trypsin, with a hydrolysis degree of 2% and 5%. Afterwards, SPI and SPH were conjugated with dextran to form a covalent complex macromolecule, which were named SPI-D, SPH2-D and SPH5-D, respectively. Covalent bond was formed between SPI/SPH and dextran molecules via the glycation reaction has been confirmed by fourier transform infrared (FTIR) spectroscopy analysis. Subsequently, the freeze-thaw stability of SPI-D and SPH-D was evaluated. After three freeze-thaw cycles, the characters of SPH-D emulsions exhibited smaller values than those of SPI-D emulsions in terms of oiling off, particle size, flocculation degree (FD) and coalescence degree (CD). In addition, SPH2-D emulsions were more stable after freeze-thaw treatment compared with SPH5-D emulsions. Optical microscopy analysis also supported the results above.

Freeze-thaw stability of oil-in-water emulsions stabilized by soy protein isolate-dextran conjugates

The soy protein isolate-dextran (SPI-D) conjugates were prepared by ultrasound (power output 500 W for 40 min) and microwave (power output 800 W for 2 min) assisted glycosylation to improve the freeze-thaw stability of soy protein isolate stabilized oil-in-water (o/w) emulsions. Fourier transform infrared and fluorescence emission spectroscopy analyses confirmed that covalent bonds were formed between soy protein isolate (SPI) and dextran molecules through the Maillard reaction. The stability of SPI, SPI+D mixture, ultrasound SPI-D conjugates (SPI-DU) and microwave SPI-D conjugates (SPI-DM) emulsions subjected to from one to three freeze-thaw cycles was investigated. In comparison with SPI and SPI+D emulsions, SPI-DU and SPI-DM emulsions exhibited smaller creaming index, oiling off, droplet diameters, flocculation degree (FD) and coalescence degree (CD) after each freeze-thaw cycle. In addition, the zeta potential and specific surface area (SSA) were greater. Appearance and microstructure indicated that SPI-DU and SPI-DM emulsions exhibited a relative stable state after three freeze-thaw cycles.

Influence of nanocomplexation with curcumin on emulsifying properties and emulsion oxidative stability of soy protein isolate at pH 3.0 and 7.0

Although the complexation between proteins and phenol compounds has been widely investigated for improved stability and delivery of those compounds, especially those with low solubility and bioavailability, few works are available addressing the influence on the functional properties of the proteins. The work investigated the influence of complexation with curcumin at pH 3.0 and 7.0 on the emulsifying properties and emulsion oxidative stability of soy protein isolate (SPI). At both test pH values, most of proteins in SPI were present in the nanoparticle form, with larger sizes, higher surface hydrophobicity and better emulsifying properties of these nanoparticles observed at pH 3.0. However, the emulsions at pH 3.0 were much more susceptible to lipid oxidation. The SPI at both pH values easily interacted with curcumin to form complexes at nanoscale, through hydrophobic interactions. The complexation at both pH values slightly changed the particle size, the absolute ξ-potential and emulsifying properties of the protein, but remarkably decreased their surface hydrophobicity. Furthermore, the complexation distinctly accelerated the lipid oxidation of the emulsions at both pH values. The results would be of importance for the development of functional soy protein ingredients enriched with some bioactive compounds.

Enhanced Physical and Oxidative Stabilities of Soy Protein-Based Emulsions by Incorporation of a Water-Soluble Stevioside–Resveratrol Complex

To strengthen the effectiveness of resveratrol (RES) as a natural antioxidant in food systems, this work attempted to enhance the water solubility of RES by utilizing the solubilizing properties of stevioside (STE) and investigated the effect of STE-solubilized RES (STE-RES) incorporation on the stability of soy protein isolate (SPI)-based emulsions. The physical properties and oxidative stability of SPI emulsions with STE/STE-RES were evaluated. The water solubility of RES increased with the increase of STE concentration up to its critical micelle concentration, suggesting the solubilization of hydrophobic RES in STE self-assembled micelles. STE micelles competitively adsorbed at the oil-water interface with SPI, forming a mixed SPI and STE interfacial layer, thus resulting in a decrease in particle size and evident enhancement in the physical stability of SPI-based emulsions. After the incorporation of STE-RES, SPI emulsions showed an enhanced oxidative stability with reduced lipid hydroperoxides and volatile hexanal. This improvement was believed to be mainly attributed to the targeted migration of RES to the interface during the adsorption of the STE-RES complex, as evidenced by high interfacial accumulation of RES.

Effect of pulsed electric field on the secondary structure and thermal properties of soy protein isolate

Changes of structure and thermal stability of soy protein isolate after pulsed electric field treatment were analyzed by Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC). When the applied pulsed electric field (PEF) treatment intensity was over 35 kV/cm, the amino acid side chain, anti-parallel β-sheets, β-turn as well as β-sheets in soy protein isolate (SPI) secondary structure were significantly changed, which suggested that PEF treatment might be a new processing method for SPI; the dipole moments of some bonds, such as C=O, C–O, and C–O–C were partially polarized, accompanying with complete denaturation of β-conglycinin and glycinin obtained from DSC. Furthermore, self-reassembly from β-turn to α-helix in SPI structure abruptly happened under intense PEF treatment condition, which suggested that the PEF treatment had induced change of the orientation of α-helix dipole moment to stabilize α-helix. This observation implies that PEF treatment technique may be a novel method for preparation of protein nanotube.

Thermal stability of soy protein isolate and hydrolysate ingredients

The objective of this study was to characterize the effects of pH, protein concentration and calcium supplementation on thermal stability, at 140°C, of soy protein isolate (SPI) and soy protein hydrolysate (SPH) ingredients. Increasing pH between 6.4 and 7.5 led to significantly (p<0.05) higher mean heat coagulation times (HCTs) at 140°C, for all soy protein ingredients at 1.8, and 3.6% (w/v) protein. Increasing protein concentration from 1.8 to 7.2% (w/v) led to shorter HCTs for protein dispersions. Calcium supplementation up to 850mg/L, except in the case of supplementation of SPI 1 with calcium citrate (CaCit), decreased HCT for soy protein ingredient dispersions, at pH 6.4 – 7.5. No significant differences (p<0.05) were found in mean HCT for dispersions supplemented with calcium chloride (CaCl2) and those supplemented with CaCit at 450, 650 and 850mg/L Ca2+, in the pH range 6.4–7.5.

Influence of polycaprolactone-triol addition on thermal stability of soy protein isolate based films

The influence of polycaprolatone-triol (PCL-T) on the thermal degradation properties of soy protein isolate (SPI)-based films was studied by thermogravimetry and infrared spectroscopy under nitrogen atmosphere. The results showed that in the absence of PCL-T the thermal degradation began between 292 °C (pure SPI films) and ca. 264 °C (SPI/SDS films with more than 20% of SDS), and these values decreased further to the range 250–255 °C for SPI/SDS/PCL-T films. At the same time, the temperature of maximum degradation rate ( T max) decreased from 331 °C (pure SPI film) to ca. 280 °C for SPI/SDS/PCL-T films with 39% PCL-T content. This behavior was also confirmed by the activation energy ( E) values associated with the thermal degradation process. Apparently, the low thermal stability of PCL-T as compared to other film constituents, along with its plasticizer characteristics, is responsible for the decreased stability of SPI/SDS/PCL-T films. The FTIR spectra of gas products evolved during the thermal degradation indicated the formation of OH, CO 2, NH 3 and other saturated compounds, suggesting that the reaction mechanism involved simultaneous scission of the C(O)–O polyester bonds and C–N, C(O)–NH, C(O)–NH 2 and –NH 2 bonds of the protein.