Soy Protein Isolate Emulsions Research Articles

Freeze-thaw stability and rheological properties of soy protein isolate emulsion gels induced by NaCl

This article focused on the freeze-thaw stability and rheological properties of soy protein isolate (SPI) emulsion gels induced by NaCl. The freeze-thaw stability was characterized by particle size, ζ-potential, and differential scanning calorimetry (DSC) measurements. The salt concentration (200–400 mM) could promote protein aggregation and improve freeze-thaw stability. The study of both linear and nonlinear rheology properties proved that SPI emulsion gels exhibited the maximal gel strength at 300 mM NaCl that could resist structure disruption and oil droplet migration. The nonlinear responses were further analyzed using Lissajous plots. Initial SPI emulsion gels had higher peak stress values at 300 mM NaCl, indicating more resistance to deformation and increased elastic-dominant behavior as well as improved freeze-thaw stability. While the area of the elastic and viscous Lissajous plots narrowed as the salt concentration exceeded 300 mM, suggesting the viscosity and elasticity decreased. Scanning electron microscopy (SEM) images further confirmed that the SPI emulsion gels had smaller pores and denser structures at 300 mM NaCl, resulting in good freeze-thaw stability. Besides, the maximum gel strength emerged in 300 mM NaCl and 100 mM NaCl before and after freeze-thaw cycles, respectively, which was due to moderate dehydration and a small amount of oil leakage from the network. These findings provide valuable information for the relationships between freeze-thaw stability and rheology property of emulsion gels.

Effect of flax gum on the functional properties of soy protein isolate emulsion gel

Soybean oil emulsion gel is often used to replace part of fat, thereby the content of saturated fatty acids was reduced in food. This paper studied the effect of flax gum (FG) on the rheological properties, thermal properties, microstructure, and gel properties of soy protein isolate (SPI) acid-induced emulsion gels. The results showed that the apparent viscosity of SPI emulsion increased with the increase of FG addition. The mechanical properties, frequency dependence and deformation resistance of the SPI emulsion gel can be significantly improved by adding an appropriate amount of FG (0.6%). The chemical stability of the protein was significantly enhanced, the thermal stability of the emulsion gel was improved, and the water retention rate of the emulsion gel was increased by adding a certain amount of FG. The study also found that the pores between the protein network were increased and the fractal dimension of the gel system (2.862–2.775) was reduced by adding FG. When the FG concentration was 0.8%, the complexity of the gel system was minimal. In summary, FG was found to play an important role in improving the properties of Emulsion Gel, enhancing thermal stability and enhancing the strength of the gel network structure in the soy protein isolate-FG gel system.

Effect of homogenizing pressure on the properties of soy protein isolate‐vitamin D3 nanoemulsion

AbstractVitamin D3 (VD3) plays an important role in maintaining the normal growth and development of the body, but VD3 is insoluble in water and has poor stability. It is easily damaged and lost during food processing, storage, and transportation. Soy protein isolate (SPI) is a natural encapsulation vehicle for hydrophobic VD3. This article focus on the effect of different homogenizing pressures on loading of VD3 in SPI emulsion system. The results of encapsulation efficiency and loading capacity show that when the SPI‐VD3 emulsion is subjected to a homogenizing pressure of 120 MPa, the maximum encapsulation efficiency is 87.63%. As the homogenization pressure increases, the particle size distribution becomes more uniform, and the average particle size became smaller and smaller. The Fourier infrared results showed that the secondary structure of the emulsion had changed after high‐pressure homogenization. The light stability and storage stability had been significantly improved when the SPI‐VD3 emulsion homogenization pressure was 120 MPa. The optical microscope showed that when the homogenization pressure was 120 MPa, the particles of the emulsion were more uniform. These results indicated that SPI could be used as a biomaterial for embedding VD3 in the food industry.Practical applicationIn this article, SPI and VD3 were used as raw materials to form a nanoemulsion under high‐pressure homogenization conditions. The light stability and storage stability of SPI‐VD3 nanoemulsion with different homogenization pressures were explored. Since VD3 has many benefits to the human body, SPI loaded with VD3 in the form of nanoemulsion can be used in food, cosmetics, and pharmaceutical industries. This article hopes to provide a basis for better adding VD3 in the food industry.

Improving freeze–thaw stability of soy protein isolate-glucosamine emulsion by transglutaminase glycosylation

This paper studies the improvement of freeze–thaw stability of emulsions by incorporating glucosamine into soy protein isolate (SPI) by using transglutaminase. The occurrence of enzymatic glycosylated SPI reaction is confirmed by SDS-PAGE. Through the measurement of creaming index and oiling off, we find that both soy protein isolate-enzymatic without glucosamine (SPI-E) and glycosylated SPI by transglutaminase (SPI-G) can effectively improve the freeze–thaw stability of emulsions. The analysis of particle size, degree of flocculation and coalescence indicates that macromolecular aggregates were formed because transglutaminase enzyme promoted glycosylation and also promoted the cross-linking of protein and protein or the internal cross-linking of protein. Therefore, the particle size of the SPI-G emulsion before freezing and thawing is larger than that of the SPI emulsion. After freeze–thaw cycles, it can be seen that although the particle size of SPI-G is increasing, it is significantly smaller than that of SPI emulsion after freeze–thaw. According to the optical microscope, it can be seen that the SPI emulsion has obvious aggregation of oil droplets after freeze–thawing, and SPI-G effectively improves oil droplet aggregation.

Competitive displacement of interfacial soy proteins by Tween 20 and its effect on the physical stability of emulsions

The competitive displacement of interfacial proteins, including soy protein isolate (SPI), casein, and modified SPIs (heat, sodium sulfite and succinic anhydride treatment), by Tween 20 was investigated. The structural characteristics of the soy proteins, such as the surface hydrophobicity, exposed free sulfhydryl content and ξ-potential, were analyzed to explore their effects on the protein displacement by Tween 20. The sequence of Tween 20 addition significantly affected the displacement of SPI and casein from the interfaces. The highest degrees of displacement of SPI and casein were 91.04% and 90.67%, respectively, when Tween 20 was added before homogenization. However, the corresponding values became 41.29% and 87.70% when Tween 20 was added after homogenization. The lower level of the latter value was mainly attributed to the fact that SPI formed viscoelastic interfacial films, as confirmed by interfacial rheological property measurements. Although both the ξ-potentials of the SPI emulsions and the mechanical strength of the interfacial protein films decreased due to Tween 20 addition, the physical stability of the emulsions was significantly enhanced. In regard to the modified SPIs, although a high surface hydrophobicity and a low content of exposed free sulfhydryl were associated with low degrees of protein displacement in some cases, the protein charge was the dominant factor affecting the displacement by Tween 20. The emulsion stability of both SPI and the modified SPIs was improved by Tween 20, likely because Tween 20 effectively reduced the hydrophobic interactions between the oil droplets by partially displacing proteins or binding to residual interfacial proteins.

Plant proteins at low concentrations as natural emulsifiers for an effective orange essential oil microencapsulation by spray drying

In this work, pea and soy proteins were used as emulsifiers on the encapsulation of orange essential oil (OEO, rich in d-limonene) by emulsification followed by spray drying. A commercial pea protein concentrate (PPC) was studied regarding its ability to act as an emulsifier, stabilize oil-in-water emulsions containing OEO, and to produce spray-dried microparticles in comparison to a commercial soy protein isolate (SPI), which is an emulsifier that has been already used on the microencapsulation of flavors. Both PPC and SPI presented low solubility in water at their natural pH; however, the even lower solubility of PPC resulted in lower adsorption at the oil-water interface. High solids oil-in-water emulsions stabilized using different concentrations of PPC or SPI (0.6–6.0 wt%) presented different physicochemical properties and physical stability due to the difference between the solubility of PPC and SPI in water. The spray-dried microparticles produced from selected SPI emulsions presented better stability during the drying stage than PPC emulsions, which resulted in higher OEO retention values (84.1–100 wt% and 92.6–97.9 wt% for PPC and SPI, respectively). Overall, the spray-dried microparticles produced using PPC or SPI present similar physical properties that promote the protection of the encapsulated OEO. Based on these results, despite its low solubility, pea protein can be used for encapsulating OEO effectively; therefore, its use as an emulsifier on the encapsulation of other different flavor compounds must be explored even further.

Effect of Ionic Strength on Freeze–Thaw Stability of Glycosylated Soy Protein Emulsion

AbstractThis study used Soy Protein Isolate (SPI), Soy Protein Isolate Hydrolysates (SPH) and Dextran (D) as raw materials. Covalent compounds were prepared by grafting soy protein isolate and soy protein isolate hydrolysate with dextran by water‐heating method, which were SPI‐D and SPH‐D, respectively. The effect of ionic strength (0–500 mM) on the freeze–thaw stability of SPI, SPI‐D, and SPH‐D emulsions was investigated. Fourier transform infrared analysis and Fluorescence emission spectroscopy analysis indicated that the structure of the protein changed. In this study, it was found that with the increase of ionic strength, the zeta potential of the three samples presented a downward trend and the surface hydrophobicity first decreased and then increased. The addition of ions effectively improved the freeze–thaw stability of the emulsions. The particle size of the emulsions changed little after freeze–thaw cycles, and coalescence degree, creaming index, and oiling off significantly decreased. Especially when the ionic strength reached 300 mM, the degree of coalescence was 248.46%, 170.92%, and 167.77%, respectively, and the oiling off was also reduced by 68.52%, 68.25%, and 59.92%, respectively. The creaming index of the SPI emulsion was 48.49% lower than the creaming index without ions. However, when the ionic strength exceeded 300 mM, the coalescence degree, creaming index, and oiling off of the emulsions increased. Optical microstructures also found that at ionic strength of 300 mM, the oil droplets produced by the three kinds of emulsion after freeze–thaw were smaller than those without ions.

Effect of high-pressure homogenization on gelling and rheological properties of soybean protein isolate emulsion gel

The effect of high-pressure homogenization (HPH) on the functional properties of soy protein isolate (SPI) emulsion gel was studied in this paper. The results show that, with the increase of HPH pressure, the strength of SPI emulsion gel raised from G’ = 291 Pa (5 MPa) to G’ = 528 Pa (80 MPa). The higher HPH pressure also reduced the frequency dependence of the SPI emulsion gel (n’ descended from 0.105 to 0.065). However, there is no monotonous relationship between the recovery rate and the HPH pressure. Water holding capacity of the emulsion gel increased from 87.7% to 91.4% (when the pressure rose from 5 to 20 MPa), and then remain stable (when the pressure rose from 20 to 80 MPa). The microscopic fractal dimension of SPI emulsion gel ranges from 2.96 to 2.99. Generally speaking, at a higher HPH pressure, the emulsion tends to form a more stable isotropic network gel structure.

Aggregation and emulsifying properties of soybean protein isolate pretreated by combination of dual-frequency ultrasound and ionic liquids

The objectives of this study were to investigate the changes in the aggregation and emulsifying properties of soy protein isolate (SPI) pretreated with dual-frequency ultrasound and three different ionic liquids (ILs), tributyl methyl ammonium chloride ([TBMA]Cl), 1-butyl-3-methyl imidazolium chloride ([BMIM]Cl) and 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM]BF4). Results showed that dual-frequency ultrasound and ILs could not change the primary structure of SPI. The changes in UV–vis spectra indicated the unfolding of SPI as pretreated by [TBMA]Cl and [BMIM]Cl combined with dual-frequency ultrasound, followed by formation of soluble aggregates. The thermal stability analysis of the regenerated SPI suggested that [BMIM]BF4 presumably broke most of the hydrogen bonds within adjacent SPI molecules, leading to the decrease of thermal stability. Transmission electron microscopy showed major changes in protein morphology upon protein–protein interactions. SPI emulsion pretreated with dual-frequency ultrasound and [BMIM]BF4 had a higher emulsion stability index than the other samples (P < 0.05). Furthermore, as compared to untreated protein, all ultrasound and ILs pretreatments decreased the creaming index of SPI emulsion. These results indicated that combination of dual-frequency ultrasound and ionic liquids could be a potential method to change the aggregation and emulsifying properties of SPI.

Effects of transglutaminase pre-crosslinking on salt-induced gelation of soy protein isolate emulsion

The salt-induced gelation behavior of soy protein isolate (SPI) emulsions was markedly influenced by microbial transglutaminase (TGase) pre-crosslinking. Rheological data showed that when SPI emulsions were incubated with TGase at low concentrations (1 and 3 U/g protein) at 50 °C for 30 min prior to gelation, no change in storage modulus (G′), but enhanced resistance to deformation of the gels was observed. Extensive crosslinking by TGase (5 U/g protein) resulted in severe decreases in gel firmness and fracture properties (yielding stress and strain), likely due to the impairment of hydrophobic bonds and the formation of coarse networks. The water-holding capacity of the gels was significantly enhanced by increased concentrations of TGase. Interactive force analysis indicated that non-covalent interactions and disulfide bonds are the primary forces involved in CaSO4-induced SPI emulsion gel, but TGase treatment may limit hydrophobic interactions within the gel network. These results are of great potential value for the application of TGase in the food industry.

Effects of different ionic strengths on the physicochemical properties of plant and animal proteins-stabilized emulsions fabricated using ultrasound emulsification.

In this study, high intensity ultrasound (HIU) was used to produce food protein stabilized emulsions under different ionic strengths (0, 25, 50, 100, 200 and 300 mM NaCl). Five plant and animal food proteins, whey protein isolate (WPI), soy protein isolate (SPI), bovine gelatin, peanut protein isolate (PPI) and corn zein were selected as protein emulsifiers. PPI and zein could not form emulsions using ultrasound emulsification at all ionic strengths (from 0 to 300 mM NaCl). However, ultrasound could induce stable emulsions using SPI, WPI and gelatin as emulsifiers. Moreover, different ionic strengths and protein types influenced the physicochemical properties of HIU induced emulsions obviously. It was found that the droplet sizes of gelatin emulsions were lower than those of SPI and WPI emulsions at salt concentrations of 300 mM NaCl. Furthermore, gelatin emulsions had better stability against environmental stresses (salt and temperature) than that of SPI and WPI emulsions. Moreover, the adsorbed protein (%) at the oil/water interface of SPI emulsions was higher than those of WPI and gelatin emulsions. However, the adsorbed protein amount of all proteins stabilized emulsions increased significantly after salt addition. The absolute ζ-potential values decreased with the increase of salt concentrations. The microrheology results indicated that the SPI emulsions formed a gel-like structure at high salt concentrations (>50 mM NaCl) as SPI emulsions exhibited higher elasticity than WPI and gelatin emulsions. In conclusion, the ultrasound as a green emulsification technique could be used to fabricate emulsions stabilized by plant and animal proteins.

Effect of pH on Freeze-thaw Stability of Glycated Soy Protein Isolate.

The effects of pH on the freeze-thaw stability of glycated soy protein isolate (SPI) and soy protein isolate hydrolysate (SPH) were studied. The covalent compounds were prepared by conjugating SPI, SPH and dextran under heated Maillard reaction, which the macromolecules were named SPI-D and SPH-D. SDS-PAGE analysis verified that SPI-D and SPH-D form a covalent bond through the Maillard reaction. Afterwards, the effects of pH on the freeze-thaw stability of SPI, SPI-D and SPH-D emulsions were evaluated. The covalent conjugate stabilized emulsions improved the stability of the emulsions to pH stress. After freeze-thaw cycles, SPH-D revealed the lowest particle size, degree of coalescence (CD) and oiling off. The results above were also supported by optical microscopy analysis.

Effect of High Pressure Treatment on Interfacial Properties, Structure and Oxidative Stability of Soy Protein Isolate-Stabilized Emulsions

The effect of high pressure homogenization (HPH) treatment (40 to 200MPa) on the structure, interfacial properties and oxidative stability of soy protein isolate emulsions were investigated. After HPH process, emulsifying activity (EAI) and emulsion stability (ESI) could be improved by 114% and 125%, percentage of protein adsorbed to oil-in-water emulsions significantly improved when the pressure was not more than 160 MPa. SDS-PAGE showed that the HPH caused more low molecular mass subunits as the samples were treated below 160 MPa. FTIR traced the changes of four conformations in the secondary structure. Within a suitable pressure range, the apparent viscosity increased with the increasing of pressure, which reflected shear thinning; rheological measurement of emulsions showed G'>G'', G' and G'' both increased significantly with frequency increasing; emulsions treated by HPH had better oxidative stability. This paper suggested the HPH was a useful method for preparation the highly viscous and stable emulsions.

Improvement of gelation properties of soy protein isolate emulsion induced by calcium cooperated with magnesium

The aim of this study is to investigate the cooperation effects of calcium (CaSO4) and magnesium (MgCl2 and MgSO4) salts on the rheological and microstructural properties, and water holding capacity (WHC) of soy protein isolate (SPI) emulsion-based tofu gels. Small-deformation rheology indicated that the aggregation power of the three coagulants follows the order of MgCl2 > MgSO4 > CaSO4, and the coagulants containing MgSO4 (5 and 10 mM) and MgCl2 (5 mM) promote to produce stronger gels with greater gel firmness and rigidity. When compared with single CaSO4 as the coagulant, a low concentration of Mg2+ helped to form compact protein aggregates and facilitated gel homogeneity and resistance to deformation. The WHC of the gels was significantly enhanced (p < 0.05) by the action of 5 mM MgSO4. The relationships between aggregates induced by the coagulants and gel properties, as well as the influencing mechanism were discussed. The findings provide valuable information for understanding the coagulant-related gelation mechanism of protein and the application of SPI emulsion-based gels with improved properties in food industry.

Investigation of the stability of vitamin D in emulsion-based delivery systems

Vitamin D is a nutraceutical agent, which is necessary for good health. However, the sufficient amount of this vitamin needed for daily intake is not found in most foods which leads to many producers choosing to develop vitamin-enriched products. Vitamin D is sensitive to the exposure to oxygen and high temperature. To protect it against degradation during food processing, emulsion-based delivery is preferred. The more stable emulsion leads to higher protection of vitamin D. The present study investigated the effects of different factors, such as the choice of biopolymer, pH, ionic strength, and temperature, on emulsion stability. As emulsions with smaller particles are known to be more stable, the minimum concentrations of the biopolymers under study allowing the minimum size of particles were determined. The results obtained were the following: gum arabic 7 %, 468 nm; maltodextrin 2 %, 266 nm; Whey protein concentrate (WPC) 0.5 %, 190 nm; Soy protein isolate (SI) 4 %, 132 nm. Among the different biopolymers and the emulsion conditions studied, the soy protein isolate emulsion provided the highest protection of vitamin D (85 %) at 4 wt% concentration, pH 7 and 25?C. SEM analysis of the dried nanocapsules of the soy protein isolate emulsion revealed homogeneous and uniform dispersion of particles.

Enhanced CaSO4-induced gelation properties of soy protein isolate emulsion by pre-aggregation

The effects of CaSO4-induced pre-aggregation on the rheological and structural properties of soy protein isolate (SPI) emulsion gels were investigated. As the Ca2+ concentration during pre-aggregation increased (from 0mM to 7.5mM), the elastic modulus of the gels showed substantial increase, indicating stiffer gel structures. Large-deformation rheology suggested stronger but more brittle networks formed at higher Ca2+ concentration during pre-aggregation. However, when the pre-aggregated Ca2+ concentration reached 10mM, the corresponding gel became weaker. Water-holding capacity (WHC) of the gels were significantly improved via the pre-aggregation process. The differences in rheological properties and WHC among the gels were consistent with the variation in their microstructures. Pre-aggregation helped to form denser and more uniform structures with thicker strands, whereas over aggregation made the gel network coarser.

Freeze-thaw stability of pickering emulsions stabilized by soy and whey protein particles

The freeze-thaw stability of Pickering emulsions stabilized by (nano)particles from heated soy protein isolate (SPI) and whey protein (WP), was investigated and compared with those stabilized by unheated SPI (or WP) and sodium caseinate (NaCN). The stability was evaluated in terms of flocculation and coalescence degrees, and creaming index, as well as differential scanning calorimetry (DSC) characteristics. The emulsions exhibited different patterns of freeze-thaw stability, depending on the type of applied proteins, as well as the cycle number of freeze-thaw treatment. In general, the emulsions stabilized by heated SPI and WP exhibited much better freeze-thaw stability against coalescence and creaming, than those by unheated counterparts. The freeze-thaw stability against creaming of the heated SPI emulsion was even much better than that of the NaCN emulsion. The emulsions stabilized by SPI or WP, unheated or heated, showed poor freeze-thaw stability against flocculation. The differences in freeze-thaw stability between different emulsions could be explained in terms of the differences in physicochemical parameters of proteins or protein particles, as well as their microstructure. The good freeze-thaw stability of the emulsions by heated SPI and WP might be largely due to the action of Pickering steric stabilization, while the gel-like network formation also attributed to the stability. The results would be of great importance for the fabrication of Pickering emulsions stabilized by food protein particles and their applications in food formulations.

Effects of the size and content of protein aggregates on the rheological and structural properties of soy protein isolate emulsion gels induced by CaSO4.

The effects of the size and content of soy protein isolate (SPI) aggregates on the rheological and textural properties of CaSO4-induced SPI emulsion gels were investigated. Considerable differences in the rheological, water-holding, and micro-structural properties were observed. The gels with larger and/or more SPI aggregates showed substantial increase in the elastic modulus and had lower gelation temperatures. Creep data suggested that the size of the SPI aggregates contributed more to the elastic modulus, whereas the increase of aggregate content enhanced the elastic modulus and viscous component of the gels. The water-holding capacity was markedly enhanced (p<0.05) with the increase in both the size and content of SPI aggregates. Confocal laser scanning microscopy and scanning electron microscopy showed that larger and/or more SPI aggregates resulted in more homogeneous networks with smaller oil droplets. These insights provide important information for the product development in relation to soy protein-stabilized emulsions and emulsion gels.

Vegetable protein isolate-stabilized emulsions for enhanced delivery of conjugated linoleic acid in Caco-2 cells

Developing edible delivery systems which offer higher protection and release of bioactive constituents is a current challenge in the food industry. The ability of oil-in-water emulsions (20% oil) stabilized by soy or pea protein isolates (4%) to deliver conjugated linoleic acid (CLA, 6%), was studied. The emulsions were prepared by conventional homogenization (550 bar) using one or five homogenization passes. The physicochemical properties of the emulsions were determined, as well as loading capacity and oxidative stability. The emulsions were subjected to in vitro digestion, and tested on absorptive Caco-2 cells. The presence of CLA isomers was followed throughout the process. When comparing similar treatments, soy protein isolate emulsions showed smaller particle size distributions than emulsions prepared with pea protein isolates. Emulsions containing soy proteins showed preferential adsorption of the α′ subunit of conglycinin and the A1, A2, A4 subunits of glycinin on the oil droplets. All emulsions protected the encapsulated CLA better than the non-emulsified control in which CLA was oxidized during storage, as well as after in vitro digestion and delivery in Caco-2 cells. Similar percentages of bioaccessibility and bioavailability of CLA were found for all the emulsion treatments. The results obtained here open new prospects for using oil-in-water emulsions as structured emulsion-based delivery systems to be used in functional foods containing CLA with health enhancing properties.

Effects of Emulsification of Fat on the Surface Tension of Protein Solutions and Surface Properties of the Resultant Spray-Dried Particles

To examine the effect of protein adsorption on the fat–water interface on the surface composition of spray-dried particles, whey, hydrolyzed whey, and soy protein isolate emulsions were prepared at three different protein to fat ratios of 1:1, 1:5, and 1:10 and spray dried. Non-hydrolyzed whey protein isolate (WPI) and the more hydrolyzed whey protein solutions at 20.2% degree of hydrolysis (DH) had significantly lower surface tension values with fat than without fat. The correlation between the reduction of surface tension value of an emulsion and the increase in protein surface composition of powder particles was observed for WPI and HWP406 but was not observed for the other protein isolate types. It was clear that the spray-dried emulsions had fat as the dominant component on the surface of the powder particles and that the amount of protein on the surface became severely depressed at higher fat addition levels. In terms of its powder morphology, the unique powder structures such as the indentations and folds usually found on the surface of protein containing powders were not evident because they were compromised by the presence of high surface fat. The powder with higher surface fat had more crumpled particle structures and dimpled surfaces.