Effect of transglutaminase-induced cross-linking on gelation of myofibrillar/soy protein mixtures

Microbial transglutaminase (MTGase)-catalyzed interaction and gelation of mixed myofibrillar (MPI)/soy (SPI) protein isolates were investigated at varying ionic strengths and MPI:SPI ratios, with or without SPI being preheated (80?°C). MTGase treatments in deionized water converted myosin heavy chain and actin into lower molecular-weight polypeptides, which gradually diminished as the ionic strength increased up to 0.6 M NaCl. A reduced intensity in the electrophoretic bands of soy proteins (7S and 11S except the basic subunits) was observed in all treatments, suggesting cross-linking with MPI. The enzyme treatment slightly increased the thermal transition (denaturation) temperatures of MPI/SPI but greatly enhanced (P<0.05) the elasticity of the mixed protein gels when compared with untreated samples, independent of incubation time.     

Formation and properties of glycinin-rich and β-conglycinin-rich soy protein isolate gels induced by microbial transglutaminase

The gelation and gel properties of glycinin-rich and β-conglycinin-rich soy protein isolates (SPIs) induced by microbial transglutaminase (MTGase) were investigated. At the same enzyme and protein substrate concentrations, the on-set of gelation of native SPI and the viscoelasticity development of correspondingly formed gels depended upon the relative ratio of glycinin to β-conglycinin. The turbidity analysis showed that the glycinin components also contributed to the increase in the turbidity of SPI solutions incubated with MTGase (at 37 °C). Textural profile analysis indicated that the glycinin components of SPIs principally contributed to the hardness, fracturability, gumminess and chewiness values of corresponding gels, while the cohesiveness and springness were mainly associated with the β-conglycinin components. The strength of MTGase-induced gels of various kinds of SPIs could be significantly improved by the thermal treatment. The protein solubility analyses of MTGase-induced gels, indicated that besides the covalent cross-links, hydrophobic and H-bondings and disulfide bonds were involved in the formation and maintenance of the glycinin-rich SPI gels, while in β-conglycinin-rich SPI case, the hydrophobic and H-bondings were the principal forces responsible for the maintenance of the gel structure. The results suggested that various kinds of SPI gels with different properties could be induced by MTGase, through controlling the glycinin to β-conglycinin ratio.     

Gelation Properties of Transglutaminase-Induced Soy Protein Isolate and Wheat Gluten Mixture with Ultrahigh Pressure Pretreatment

In this study, we elucidated the microbial transglutaminase-induced gelation properties and thermal gelling ability of soy protein isolate (SPI) and wheat gluten (WG) mixture following ultrahigh pressure (UHP, 100–400 MPa) pretreatment. UHP treatment induced unfolding and aggregation within SPI/WG protein molecules, which led to increases in free sulfhydryl group content and surface hydrophobicity. However, the transglutaminase cross-linking reaction facilitated the formation of hydrophobic interactions and disulfide bonds and thus resulted in higher gel strength, water holding capacity, and denser and more homogeneous gel networks of transglutaminase cross-linked SPI/WG gels. Rheological measurements revealed that the addition of UHP steps might generate a higher storage modulus (G′) value of MTGase-induced SPI/WG gelation during the heating-cooling cycle (25 °C → 95 °C → 25 °C). Our results indicated that various chemical interactions including covalent interactions (i.e., ε-(γ-glutamyl)lysine bonds and disulfide bonds) and non-covalent interactions (i.e., electrostatic forces and hydrophobic interactions) were involved in SPI/WG gel network structures. Hydrophobic interactions and disulfide bonds are significantly increased with the pressure level (100–400 MPa) compared with that of the unpressurized control. Furthermore, UHP treatment reduced the α-helix and β-turn content but increased the β-sheet and random coil structures. Thus, UHP treatment may be considered as a novel technique to expand the utilization of SPI/WG mixture in the food protein gelation industry.     

Effects of CaCl<Subscript>2</Subscript> on chemical interactions and gel properties of surimi gels from two species of carps

Effects of CaCl₂ on chemical interactions, textural properties and expressible moisture content of suwari and kamaboko gels from yellowcheek carp and grass carp were investigated. And the correlations between the contents of chemical interactions and physical properties of surimi gels were analyzed. The contents of chemical interactions, especially non-disulfide covalent bonds, disulfide bonds and hydrophobic interactions of suwari and kamaboko gels, varied with addition concentration of CaCl₂ and fish species. Suwari and kamaboko gels from yellowcheek carp exhibited higher breaking force, deformation and gel strength than these from grass carp. Surimi gels (suwari and kamaboko gels) from yellowcheek carp and grass carp exhibited their maximum gel strength when 40 mmol/kg and 100 mmol/kg CaCl₂ was added, respectively. Addition of CaCl₂ at high concentration resulted in low water holding capacity of surimi gels. Correlation analysis indicated that the contents of nonspecific associations, ionic bonds, hydrophobic interactions and sulfhydryl groups exhibited significant correlation with breaking force of surimi gels from yellowcheek carp and grass carp. Additionally, the content of non-disulfide covalent bonds had significant positive correlations with breaking force and expressible moisture of surimi gel from yellowcheek carp.     

Gelation enhancement of soy protein isolate by sequential low‐ and ultrahigh‐temperature two‐stage preheating treatments

The effects of combined two heating steps with low (LT, 60 °C for 1 h) and ultrahigh (UHT, 130 or 140 °C for 4 s) temperatures on the thermal gelation of soy protein isolate (SPI) were studied. UHT pretreatments significantly increased protein solubility and enhanced the gelling potential of SPI. Yet, the two‐stage preheating treatment with LT and then UHT‐130 °C had a most remarkable effect: the gel strength of the SPI₆₀₊₁₃₀ sample was, respectively, 1.45‐, 1.64‐ and 3.19‐fold as strong as those of SPI₆₀, SPI₂₅₊₁₃₀, and SPI₂₅. In comparison with single LT or UHT treatments, this two‐stage heating also produced greater amounts of soluble protein aggregates stabilised predominantly by disulphide bonds and hydrophobic forces, contributing to the improved gel network structure.     

The relationship between breaking force and hydrophobic interactions or disulfide bonds involved in heat-induced soy protein gels as affected by heating time and temperature

Hydrophobic interactions and disulfide bonds involved in heat-induced soy protein gels were characterised by determining the dissolution kinetics of gels. Reducing SDS-PAGE results revealed that all proteins in gel network could be dissolved simultaneously by 1% (w/v) SDS solution, while a majority of glycinin (11S) A polypeptide and a moderate amount of 11S-B polypeptides, 7S-α′, α, γ, and β subunits were found in 2% (w/v) DTT dissolving samples. Stronger interaction force between proteins in gel network would result in lower dissolution constant rate. The breaking force of soy gels increased from 543 to 2171 g_force with increasing heating temperature from 85 to 100 °C, and denaturation of 11S globulins played an important role in the development of gel network. As increasing heating time from 30 to 120 min, the breaking force of gels increased from 1687 to 2175 g_force, then decreased to 1253 g_force when the time was prolonged to 240 min. Negative correlations were observed between breaking force and dissolution constant rate k_SDS or Δk, which suggested that the strengthening of both hydrophobic interactions and disulfide bonds.     

Effect of soy protein substitution for sodium caseinate on the transglutaminate-induced cold and thermal gelation of myofibrillar protein

The influence of soy protein isolate (SPI) substitution for sodium caseinate (SC) on the properties of cold-set (4 °C) and heat-induced gels of pork myofibrillar protein (MP) incubated with microbial transglutaminase (TG) was investigated. The strength of cold-set MP–SC gels (formed in 0.45 M, NaCl, 50 mM phosphate buffer, pH 6.25) increased with time of TG incubation, but those gels with more than 66% SPI substituted for SC had a >26% reduced strength (P < 0.05). Upon cooking, both incubated and non-incubated protein sols were quickly transformed into highly elastic gels, showing up to 6000 Pa in storage modulus (G′) at the final temperature (72 °C). However, no differences (P < 0.05) in G′ were observed between heated samples with SPI and SC. Myosin heavy chain, casein and soy proteins gradually disappeared with TG incubation, contributing to MP gel network formation. Both cold-set and heat-induced gels had a compact protein matrix, attributable to protein cross-linking by TG.     

Effect of soy protein isolate on gel properties of Alaska pollock and common carp surimi at different setting conditions

The effects of soy protein isolate (SPI) on the gel properties of different grade Alaska pollock and common carp surimi at different setting conditions were evaluated and compared. Breaking force and distance of gels decreased with increasing SPI concentrations in direct cook (85 °C for 30 min) and in cook after setting at 30 °C for 60 min conditions. The effect of SPI on gel strength of common carp surimi was less than in Alaska pollock surimi. The breaking force obtained for addition of 10% SPI to Alaska pollock surimi was higher than for surimi alone when cooked after incubation at 50 °C for 60 min. Addition of SPI decreased the whiteness and increased the yellowness of the gel. The gel structure showed that the addition of SPI modified the microstructure of the fish protein gel, thus resulting in surimi with different gelling properties. Copyright © 2004 Society of Chemical Industry     

Physical properties of emulsion gels formulated with sonicated soy protein isolate

This study aimed to determine the effect of high-intensity ultrasound (HIU) on physical properties of soy protein isolate dispersions (SPI) and their addition to emulsion gels (EG) containing soybean oil (SBO), inulin (IN) and carrageenan (CAR). Sonicated and non-sonicated SPI dispersions were mixed with CAR, IN and SBO and heated at 90 °C for 30 min to gel the emulsion. An increase in solubility and oil binding capacity was observed in sonicated SPI dispersions (S-SPI) compared to the non-sonicated ones. HIU changed the molecular weight of SPI and decreased apparent viscosity in the dispersions. The use of S-SPI in the EG reduced the droplet size and increased the hardness and G′ values. The use of S-SPI allowed a reduction of 75% of carrageenan in the EG without affecting the hardness of the gel. The results suggest that HIU can be used to improve rheological properties of functional EG.     

Molecular interactions and functionality of a cold-gelling soy protein isolate

ABSTRACT:  A soy protein isolate (SPI) was thermally denatured at a critical concentration of 8% protein for 3 h at 95 °C, resulting in a powder that was readily reconstituted at ambient temperature and that demonstrated improved heat stability and cold-set gel functionality when compared to a control SPI. When SPI was heated at 3% protein equivalently, prior to reconstitution to 8% protein, the final viscosity was about 3 orders of magnitude less than the original sample. The viscosity of SPI heated at 3% protein was still nearly 2 orders of magnitude less than the original sample after both samples were reheated at 8% protein. These results suggested that heat denaturation at low protein concentrations limited network formation even after the protein concentration and interaction sites increased, impacting the isolate's cold gelling ability. Gelation was prevented upon treatment of SPI with iodoacetamide, which carbaminomethylated the cysteine residues, establishing the role of disulfide bonds in network formation. The viscosity of the 8% protein dispersion was also reduced by 2 orders of magnitude when treated with 8 M urea, and when combined with 10 mM DTT the gel viscosity was decreased by another order of magnitude. These results suggested that hydrophobic interactions played a primary role in gel strength after disulfide bonds form. The need for a higher concentration of protein during the heating step indicated that the critical disulfide bonds are intermolecular. Ultimately, the functionality produced by these protein–protein interactions produced a powdered soy protein isolate ingredient with consistent cold-set and thermal gelation properties.     

Interactions between soy protein isolate and xanthan in heat-induced gels: The effect of salt addition

The influence of xanthan and/or KCl addition on the properties of heat-induced soy protein isolate (SPI) gels at pH 3.0 was studied. Changes in protein solubility and subunit composition as well as in the mechanical properties, microstructure and water holding capacity of the gels were determined. The effect of KCl addition on each biopolymer solution was also investigated. The results indicated that SPI–xanthan gels prepared without KCl were mainly stabilized by non-covalent (H-bonding and hydrophobic) and SS bond interactions, whereas in gels containing KCl, electrostatic interactions were also involved in maintaining the gel structure. The β-7S subunit was probably the fraction electrostatically linked to the xanthan. The different values found for the mechanical properties after the addition of xanthan and/or KCl, were associated with the coarseness of the gel. Xanthan and KCl probably showed a synergistic effect on the Young modulus because KCl induced a conformation transition of the xanthan molecules.     

Effects of β‐glucans on properties of soya bean protein isolate thermal gels

The effects of concentration and molecular weight of oat β‐glucans on properties of soya bean protein isolate (SPI) thermal gels prepared by heating at 90℃for 30 min were investigated. Compared with control (free of β‐glucan) formulations, the presence of β‐glucans (0.5–1.5%, w/v) largely enhanced storage modulus (G′) and texture properties of SPI (12%, w/v) thermal gels measured by dynamic oscillatory rheometry and texture profile analysis, which were developed as increasing β‐glucan concentration and molecular weight. It is possible that β‐glucans could cause the formation of protein aggregates to produce gels through hydrophobic interactions. Mixed gel systems at low ionic strength showed higher G′ resulting from the lower denaturation temperature of SPI, which was beneficial to the formation of gel structure. In addition, although adding a certain amount of β‐glucan into SPI reduced water‐holding capacity of mixed gels, high molecular weight of β‐glucan improved their water‐holding capacity compared to control formulations attributed to the improvement of the structural integrity of the mixed gel network.     

Assessment of the effects of soy protein isolates with different protein compositions on gluten thermosetting gelation

Although soy proteins are known to have a deleterious effect on gluten thermosetting gelation, the causes are still poorly understood. Different sources of soy protein isolates (SPI) were used to investigate the interactions between gluten and soy proteins during hydro-thermal treatments. Commercial SPI and isolates prepared from soybean lines with different subunit composition were used to study the influence of protein denaturation and subunit composition on thermoset gel formation. Rapid Visco Analyser analysis showed that replacement of gluten with more than 1% SPI decreased the peak viscosity and interfered with formation of thermoset gels. However, peak viscosity was higher for 11% gluten + 2% SPI than for 11% gluten alone, suggesting a cooperative effect. After heating and cooling, 11% gluten + 2% SPI rich in A1 and A2 subunits formed a coherent thermoset gel suggesting that the cysteine residue content of soy proteins can affect gel formation.     

The effect of pH on the gelling behaviour of canola and soy protein isolates

The present study investigates the gelation mechanisms of a canola protein isolate (CPI) as a function of a pH (3.0–9.0), and compares it to that of a commercial soy protein isolate (SPI). A rheological investigation found that CPI was non-gelling at pH 3.0, and then formed a gel with increasing strength as pH was raised from pH 5.0 to 9.0. In contrast, the commercial SPI ingredient was found to be non-gelling at pH 9.0, but formed the strongest networks at pH 5.0 near its isoelectric point (pI = 4.6). Denaturation temperature as determined by differential scanning calorimetry were found to occur at ~ 78 °C for CPI at pH 5.0, then shifted to higher temperatures (~ 87 °C) at pH 7.0/9.0, whereas detection of SPI denaturation could not be obtained due to instrument sensitivity. Gelling temperatures were similar for both CPI and SPI (~ 82–86 °C) at all pHs, with the exception of SPI at pH 5.0 (~ 46 °C). Overall CPI networks were stronger than SPI, since the latter had weaker inter- and intramolecular junction zones. Confocal laser scanning microscopy images indicated that CPI gels became denser with lower lacunarity values as pH increased from 3.0 to 9.0. Moreover, the fractal dimension of CPI gels was found to increase from ~ 1.5-1.6 to ~ 1.8 as pH increased from 5.0/7.0 to 9.0, respectively suggesting diffusion-limited cluster-cluster aggregation. Images of SPI networks were not concurrent with fractal analysis under the conditions examined. Despite CPI having excellent gelling properties that are comparable to SPI, its need for alkaline pH conditions will limit its applicability in foods.     

Gel properties of surimi from silver carp (Hypophthalmichthys molitrix) as affected by heat treatment and soy protein isolate

The effects of setting conditions and soy protein isolate (SPI) on textural properties of surimi produced from silver carp were investigated. Effects of setting temperature, setting time and protein concentration on the gel strength were evaluated and compared utilizing response surface methodology. Models for breaking force and breaking distance of silver carp surimi were established. The total protein content was 13.4% in all experimental samples. Setting temperature and protein concentration were the major factors affecting the gel strength. In the range of the additive SPI protein (10–40%), breaking force and distance of silver carp surimi gels decreased when the protein ratio of SPI was increased in the total protein at 30 and 40 °C for 60 min setting and heating at 85 °C for 30 min, but the breaking force obtained for 90% surimi protein plus 10% SPI protein was higher than surimi alone at 50 °C for 60 min incubation and heating at 85 °C for 30 min.     

分子间作用力对大豆蛋白凝胶形成的影响

本实验用大豆分离蛋白模拟传统豆腐的凝胶形成过程,研究分子间作用力对大豆蛋白凝胶形成过程及质构特性的影响。结果表明,大豆蛋白凝胶的形成过程受多种分子间作用力的影响,其中静电作用、疏水相互作用和氢键对石膏凝固大豆蛋白凝胶的形成具有重要的影响。     

Improvement of pea protein gelation at reduced temperature by atmospheric cold plasma and the gelling mechanism study

Pea protein as an alternative of soy protein has attracted growing interest in food industries. However, high temperature (> 95 °C) is required to enable heat-induced gelation and the formed gels are relatively weak. This research aimed to study the efficacy of atmospheric cold plasma (ACP) as a novel non-thermal technique to improve the gelling properties of pea protein. While native pea protein concentrate (PPC) (12 wt%) could not form gel under 90 °C, ACP-treated PPC showed good gelling properties when heated at 70–90 °C. The gels exhibited homogeneous three-dimensional network structure with interconnected macropores, and those prepared at 80 and 90 °C possessed good mechanical strength and viscoelasticity, as well as high water holding capacity. The gelling mechanism was studied by monitoring pea protein structural changes during ACP treatment and gel formation process via a transmission electron microscope, a Fourier transform infrared spectrometer, and a rheometer. These results revealed that ACP treatment contributed to the formation of protein fibrillar aggregates, and significantly reduced the PPC denaturation temperature, leading to protein unfolding at reduced temperature of 80–90 °C. ACP treatment also increased the protein surface hydrophobicity and exposed free sulfhydryl groups, which could facilitate the formation of hydrophobic interactions and disulfide bonds, leading to gels with improved mechanical properties. Moreover, hydrogen bonding could play an important role to stabilize the gel network during the gelling process. Owing to the short exposure time and energy efficiency, ACP is a promising technology to enable wide applications to pea protein as a gelling ingredient of plant protein-based food products, such as meat analogues and egg alternatives.     

Surface Properties of Heat‐Induced Soluble Soy Protein Aggregates of Different Molecular Masses

Suspensions (2% and 5%, w/v) of soy protein isolate (SPI) were heated at 80, 90, or 100 °C for different time periods to produce soluble aggregates of different molecular sizes to investigate the relationship between particle size and surface properties (emulsions and foams). Soluble aggregates generated in these model systems were characterized by gel permeation chromatography and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Heat treatment increased surface hydrophobicity, induced SPI aggregation via hydrophobic interaction and disulfide bonds, and formed soluble aggregates of different sizes. Heating of 5% SPI always promoted large‐size aggregate (LA; >1000 kDa) formation irrespective of temperature, whereas the aggregate size distribution in 2% SPI was temperature dependent: the LA fraction progressively rose with temperature (80→90→100 °C), corresponding to the attenuation of medium‐size aggregates (MA; 670 to 1000 kDa) initially abundant at 80 °C. Heated SPI with abundant LA (>50%) promoted foam stability. LA also exhibited excellent emulsifying activity and stabilized emulsions by promoting the formation of small oil droplets covered with a thick interfacial protein layer. However, despite a similar influence on emulsion stability, MA enhanced foaming capacity but were less capable of stabilizing emulsions than LA. The functionality variation between heated SPI samples is clearly related to the distribution of aggregates that differ in molecular size and surface activity. The findings may encourage further research to develop functional SPI aggregates for various commercial applications.     

Effect of corn oil and amylose on the thermal properties of native soy protein and commercial soy protein isolate

Differential scanning colorimetry (DSC) was used to estimate thermal property differences between a commercial soy protein isolate (SPI) and milled defatted soy protein flour (MDF). The measurements were determined in the presence of 15, 20, 25, and 30% corn oil and 2, 4, and 6% amylose. SDS-PAGE showed that the SPI material contains aggregates as a result of the isolation procedures and processing. Upon DSC, this protein isolate showed a 7S protein transition peak at 77 °C and an 11S peak at 170 °C, while the MDF sample had a 7S peak at 69 °C and 11S peak at 177 °C. The MDF sample showed ΔH values 4 times greater than that of the SPI sample. These values reflect the effect of the isolation process on the protein. In the presence of corn oil, the MDF sample showed three transition peaks while the SPI sample displayed only two. The MDF sample demonstrated more interaction with oil than did the SPI sample. The change in the ΔH was reflective of this interaction. The addition of amylose to the SPI sample resulted in the appearance of a third peak. Amylose had a mixed effect on the two proteins; peaks of the same protein reacted differently to amylose level. Increasing the amylose level had the most influence on the third peak of the MDF sample. Amylose influence on the two proteins was attributed to a reduction of the amount of free oil in the system.     

Gelling of microbial transglutaminase cross-linked soy protein in the presence of ribose and sucrose

Soy protein isolate (SPI) was incubated with microbial transglutaminase (MTGase) enzyme for 5 (SPI/MTG(5)) or 24 (SPI/MTG(24)) h at 40 °C and the cross-linked SPI obtained was freeze-dried, and heated with 2% (w/v) ribose (R) for 2 h at 95 °C to produce combined-treated gels. Longer incubation period resulted in more compact and less swollen SPI particle shape when reconstituted with sugar solution. Thus, this MTGase treatment affected samples in terms of flow behaviour and gelling capacity. Rheological study showed different gelling profiles with the cross-linking treatments and combined cross-linked SPI gave a higher G′ value compared to single treated samples. These are due to the formation of additional ε-(γ-glutamyl)lysine bonds and “Maillard cross-links” within the SPI protein network during the MTGase incubation and heating in the presence of ribose (i.e. reducing sugar). Network/non-network protein analysis found that network protein increased with cross-linking treatment, which also resulted in different SDS–PAGE profiles. As in non-network protein fraction, A₄ subunit was suggested to become part of the network protein as a result of combined cross-linking.