Commercial Soy Protein Research Articles

Effects of soy protein hydrolysis and polysaccharides addition on foaming properties studied by cluster analysis

The objective of the work was to study foaming properties (foam overrun, drainage rate and collapse stability) of soy protein and their hydrolysates as affected by polysaccharides. As starting material a sample of commercial soy protein isolate was used (SP) and hydrolysates of 0.4, 5.0 and 5.2% degree of hydrolysis (DH) were produced by an enzymatic reaction. The polysaccharides added were xanthan, λ and κ-carrageenan, guar, locust bean gum and hydroxypropylmethylcelluloses as surface-active polysaccharides. The effect of polysaccharides addition on foaming properties depended in a complicated way on the degree of hydrolysis of protein, surface-activity of polysaccharide, concentration of both macromolecules, contribution of polysaccharide consistency to bulk viscosity and interfacial interactions between biopolymers. However, through cluster analysis the best combination of protein/polysaccharide to obtain defined foaming properties could be determined for an eventual industrial application.

Effect of pH on the properties of soy protein–pectin complexes

The interactions of a commercial soy protein isolate (SPI) and a 2:1 SPI:high methoxy pectin (PEC) complex were evaluated over a range of pH values (3–7). The SPI formed very large (> 50 μm) and largely insoluble aggregates (< 10%) close to its isoelectric point (IEP, pH 4 and 5) and smaller, more soluble (> 80%) particles at higher and lower pH values. The addition of PEC increased the solubility of SPI close to its IEP (pH 4 and 5) and prevented the formation of very large aggregates. However, PEC reduced the solubility of SPI at higher and lower pH values presumably via a depletion mechanism. The ζ-potential of diluted SPI dispersions decreased from positive to negative with increasing pH, passing through zero at pH 4.6, the isoelectric point (IEP) of the protein. At pH < 6, the addition of PEC reduced the charge of the protein suggesting the formation of a complex while at pH 6 or 7 there was no evidence of complex formation. The increased SPI solubility in the IEP in the presence of PEC is probably due to the formation of charged complex which do not aggregate while the decreased solubility of protein in the presence at high and low PEC is probably due to the formation of insoluble complexes and a depletion interaction respectively. Thermal treatment (30 min, 90 °C) enhanced the solubility of the SPI:PEC complexes close to the IEP (pH 4 and 5), but reduces it at low pH (pH 3). The SPI:PEC complexes could be manufactured in the form of a beverage at pilot scale where their solubility was enhanced by homogenization.

Absolute Bioavailability of Isoflavones from Soy Protein Isolate-Containing Food in Female Balb/c Mice

Soy isoflavones, genistein and daidzein, are widely consumed in soy-based foods and dietary supplements for their putative health benefits; however, evidence for potential adverse effects has been obtained from experimental animal studies. An important prerequisite for understanding the pharmacodynamics of isoflavones is better information about pharmacokinetics and bioavailability. This study determined the bioavailability of genistein and daidzein in a mouse model by comparing plasma pharmacokinetics of their aglycone and conjugated forms following administration of identical doses (1.2 mg/kg genistein and 0.55 mg/kg daidzein) by either an intravenous injection (IV) or gavage of the aglycones in 90% aqueous solution vs a bolus administration of equimolar doses delivered in a food pellet prepared using commercial soy protein isolate (SPI) as the isoflavone source. The bioavailability of genistein and daidzein was equivalent for the gavage and dietary routes of administration despite the use of isoflavone aglycones in the former and SPI-derived glucosides in the latter. While absorption of total isoflavones was nearly quantitative from both oral routes [>84% of areas under the curve (AUCs) for IV], presystemic and systemic phase II conjugation greatly attenuated internal exposures to the receptor-active aglycone isoflavones (9-14% for genistein and 29-34% for daidzein based on AUCs for IV). These results show that SPI is an efficient isoflavone delivery vehicle capable of providing significant proportions of the total dose into the circulation in the active aglycone form for distribution to receptor-bearing tissues and subsequent pharmacological effects that determine possible health benefits and/or risks.

Functional properties and chemical composition of fractionated brown and yellow linseed meal ( Linum usitatissimum L.)

Considering its high content of protein and dietary fiber, linseed meal is a remarkable source for food ingredient and food additive production. In this study, brown and yellow linseed meal ( Linum usitatissimum L.) were fractionated via pH control, to obtain five linseed meal fractions rich in protein and fiber. The fractions were characterized by measuring functional properties, proximate and carbohydrate composition, and lignan contents. Acid soluble protein fractions were characterized by lower emulsification capacities and foaming activities in comparison to a commercial soy protein isolate. Alkaline soluble protein fractions showed emulsification activities comparable to whole egg and relatively high contents of secoisolariciresinol diglucoside (SDG) of 110 mg/g DM and 56.2 mg/g DM, respectively. The good emulsification and foaming activities, as well as the enriched concentration of SDG and therefore high nutritional value, make especially the alkaline soluble protein fraction highly interesting for food ingredient production.

Gelation properties of salt-extracted pea protein induced by heat treatment

Gelation is one of the most important properties of plant proteins. In this paper, a low denaturation salt extraction method was used to extract pea (Pisum sativum L.) protein isolate from commercial pea flour. The gelation properties of this isolate were examined and compared to commercial products. The pea protein isolate followed the three-step process of gelation that is generally accepted for heat-induced gelation of globular proteins. The minimum gelation concentration of salt-extracted pea protein isolate (PPIs) was 5.5% while that of commercial pea protein isolate (PPIc) was 14.5%. The gelling point was in the range of 82–86 °C for 14.5% PPIs, 0.3 M NaCl at natural pH (5.65). With increasing heating rate, the gelling point tended to increase. Higher heating and cooling rates resulted in decreased final G′ (storage modulus) and G″ (loss modulus) values, indicative of decreased gel strength. A higher protein concentration resulted in higher G′ and G″ values and it was found that there was a power law relationship between protein concentration and G′ and G″. Tan delta (δ) values decreased with increasing protein concentration and at concentrations of 5.5% and above, tan δ remained constant which means the critical concentration for gel formation was 5.5%. The values of G′ and G″ for PPIs were greater than those of PPIc, and tan δ of PPIs was smaller, indicative of a stronger gel network. DSC data showed that PPIc had undergone denaturation whereas PPIs had not (ΔH = 15.81 J/g protein). Although rheometer data showed that the final G′ value of commercial soy protein isolate (SPIc) was smaller than that of PPIs, the gel prepared with SPIc was visually stronger than that of PPIs. The rheological data obtained with small amplitude oscillatory testing was not consistent with the actual observations. Overall, the low degree of denaturation of the PPIs resulted in a stronger gel than that of PPIc making the PPIs a more attractive food ingredient.

Interfacial and foaming properties of soy protein and their hydrolysates

The objective of the work was to study the impact of soy protein hydrolysis on foaming and interfacial properties and to analyze the relationship between them. As starting material a sample of commercial soy protein isolate was used (SP) and hydrolysates were produced by an enzymatic reaction, giving hydrolysates from 0.4% to 5.35% degree of hydrolysis (DH). In this contribution we have determined foam overrun (FO), stability against liquid drainage and foam collapse, and the apparent viscosity of foams produced by a whipping method. The surface properties determined were the adsorption isotherm and surface dilatational properties of two hydrolysates (2 and 5.35% DH, H1 and H2 respectively). The hydrolysis of soy proteins increased the surface activity at bulk concentrations where SP adopts a condensed conformation at the monolayer. At concentrations where it adopts a more expanded conformation a very low degree of hydrolysis (H1) also promoted the enhancement of surface activity. However, at 5.35% degree of hydrolysis (H2) the surface activity decreased. Moreover, H2 presented lower surface activity than H1 at every bulk concentration. The hydrolysis increased the elastic component of the dilatational modulus and decreased phase angle of films at bulk concentrations below that corresponding to the collapse of SP monolayer (2% bulk protein). SP hydrolysis increased foam overrun and the stability against drainage that could be related to increased surface activity of protein hydrolysates. However, the collapse of foams was promoted by hydrolysis and could be ascribed to a decrease of the relative viscoelasticity (higher phase angle) of surface films. The results point out that a low degree of hydrolysis (2–5%) would be enough to improve the surface activity of SP, decrease foam drainage and maintaining a considerable viscoelasticity of the surface films to retard foam collapse.

Carbohydrate moieties on the in vitro immunoreactivity of soy β-conglycinin

Abstract β-Conglycinin is a functional glycoprotein and one of the most important soybean allergens. The aim of the present research was to investigate the role of the N-glycans moieties of β-conglycinin on its in vitro immunoreactivity. The soy allergen was obtained by isoelectric precipitation from commercial soy protein isolate and was enzymatically deglycosylated by PNGase F (Peptide N-Glycosidase F EC 3.5.1.52). In order to optimize deglycosylation conditions different reaction times and allergen concentrations were tested. The extent of deglycosylation was estimated by SDS–PAGE, CZE, RP-HPLC, and MALDI-TOF MS analyses, which provided information related to changes in protein structure. The antigenicity of both native β-conglycinin and its deglycosylated form was evaluated by western-blotting and indirect ELISA employing polyclonal rabbit anti-soybean sera and horseradish peroxidase-labeled goat anti-rabbit IgG while the in vitro allergenicity was assessed by means of indirect competitive inhibition ELISA employing human sera (IgE) of soy allergics. β-Conglycinin was effectively deglycosylated by PNGase F. Data on immunological tests suggested that glycosyl moieties forming this glycoprotein might be involved in its immunoreactivity.

Formation of soluble aggregates from insoluble commercial soy protein isolate by means of ultrasonic treatment and their gelling properties

The formation of soluble aggregates from insoluble precipitates of commercial soy protein isolate (SPI) by means of combined homogenization and ultrasonic treatment was characterized. The heat-induced gelation of formed soluble aggregates was also investigated. The turbidity and electrophoresis analyses showed that initially insoluble precipitates of commercial SPI, most basic subunits of glycinin included, were transformed into soluble aggregates. High performance size exclusion chromatography (HPSEC) analysis confirmed the formation of soluble aggregates. Both non-covalent and covalent interactions, e.g. hydrophobic interactions, hydrogen bonds and disulfide bonds, were involved in the formation of soluble aggregates. The formation of soluble aggregates remarkably improved the heat-induced gelling ability of commercial SPI.

Effect of Microbial Transglutaminase on Spaghetti Quality

To examine the potential application of microbial transglutaminase (MTG) on semolina dough properties and quality of raw and cooked spaghetti, the effects of various MTG addition levels on the solubility of proteins, SDS-PAGE pattern of semolina dough proteins, and textural and structural properties of raw and cooked spaghetti were investigated using semolina from a high-protein good variety (MACS 1967) and a low-protein poor variety (PDW 274) durum wheat. To increase the concentration of lysyl residues and possibly enhance the extent of cross-linking of protein matrix by MTG, a commercial soy protein isolate (SPI) was added at a level of 3% (w/w) in combination with MTG, and its effect on semolina dough properties and spaghetti quality was investigated. The addition of MTG significantly decreased the solubility of semolina dough proteins. SDS-PAGE results showed that with increasing levels of MTG, a progressive decrease in the intensity of the bands corresponding to molecular weight of around 66 kDa was observed. Protein cross-linking reaction catalyzed by MTG resulted in changes in dough properties, dry spaghetti quality, cooking quality characteristics, and microstructure of cooked spaghetti. However, the quality improvements were more evident in spaghetti from the poor variety PDW 274 than from the good variety MACS 1967. The results also showed the ability of MTG in the formation of heterologous polymers between SPI and durum wheat proteins to improve the quality of spaghetti samples.

Influence of soy protein on rheological properties and water retention capacity of wheat gluten

A better understanding of the physicochemical and rheological changes in soy/wheat composite dough may lead to overcome the problems caused by the incorporation of high levels of soy products on bread formulation. The effects of commercial soy protein isolate (SPI) on uniaxial extension and creep behavior, microstructure and free water of hydrated gluten were studied. Different solid:moisture ratios were used. Results showed that the substitution of wheat protein by soy protein negatively affected the gluten–SPI mixture rheological properties due to network weakening. It was demonstrated that gluten was weakened as a consequence of the interference effect of soy proteins on their structure, and the smaller availability of water to the build-up of the gluten network. A greater amount of moisture could partially improve the rheological performance of the gluten–SPI mixture.

Transglutaminase treatment of pea proteins: Effect on physicochemical and rheological properties of heat-induced protein gels

Rheological properties of heat-induced pea protein isolate (PPI) gels with added microbial transglutaminase (MTGase) were studied under various reaction conditions. A positive linear relationship was observed between level of MTGase used (0 to 0.7% w/w) and shear stress and shear strain of heat-set commercial pea protein isolate (PPIc) gels at 92 °C following incubation at 50 °C. Use of MTGase allowed for preparation of PPIc gels of similar strength and elasticity as commercial soy protein isolate gels and commercial meat bologna. MTGase treatment did not alter thermal properties of PPI gels. The shear stress and strain of PPIc gels were also improved following low temperature (4 °C) incubation of PPI with MTGase. Enhancement of shear strain or gel elasticity of heat-induced PPI gels with MTGase has not been reported before and provides opportunities for extending the properties of pea proteins when developing new food products.

Protein–Protein Interactions in High Moisture‐Extruded Meat Analogs and Heat‐Induced Soy Protein Gels

AbstractTwo commercial soy protein isolates were made into fibrous meat analogs by high moisture extrusion or into gels by heating and cooling, at varying concentrations and/or temperatures. Protein–protein interactions by extrusion or gelation were investigated through protein solubility studies of raw and finished products. All samples except for extrudates exhibited similar patterns of solubility in four selected extractants. Phosphate buffer (PB) extracted the least amount of protein. Addition of dithiothreitol (DTT) to PB improved protein solubility, indicating the presence of disulfide bonds. PB + Urea and PB + Urea + DTT gave the highest and almost equal amount of extractable proteins from all samples, except for the extrudates from which protein could not be extracted effectively by PB + Urea, implying that disulfide bonding was more pronounced during extrusion than gelation. The results support our hypothesis that soy protein gels and extrudates both have the same types of chemical bonds, namely covalent disulfide bonds and non‐covalent interactions. It is the relative proportion of each type of bonds in their structures that differentiates the two with respect to reversibility and structure rigidity. In forming protein gels during heat‐induced gelation, non‐covalent bonds play a dominant role over disulfide bonds; whereas for forming the fibrous structure of protein extrudates, non‐covalent bonds and covalent disulfide bonds are both important.

Dynamic Viscoelastic Behavior of High Pressure Treated Soybean Protein Isolate Dispersions

Commercial soy protein isolate (SPI) dispersions (10, 15, and 20% concentrations) were subjected to high pressure treatment at selected pressure levels (350, 450, 550, and 650 MPa) for 15 minutes at 23 ± 1.5°C. Calorimetric studies confirmed denaturation of SPI dispersions at 350 MPa irrespective of concentration. Frequency sweep data (0.1 to 10 Hz) of SPI dispersions during oscillation rheological measurement demonstrated that elastic modulus (G′) predominate over viscous component (G″) for all concentrations. Gel rigidity of pressurized samples, estimated by mechanical spectra analysis, showed no systematic pattern with applied pressure however concentration significantly increased mechanical strength. Contrary to thermal effect, high pressure treated samples exhibited predominant viscous property and overall there was no significant change on viscoelastic properties of treated samples to control. Electrophoresis results (both Native and SDS) confirmed rheological data with insignificant conformational change in protein subunits of post-process samples. As expected, thermal induced gel was firmer than that of pressure treated samples at similar concentration.

Functional properties and in vitro digestibility of buckwheat protein products: Influence of processing

The effect of processing on some functional properties and in vitro digestibility of buckwheat protein products (BWP) was investigated. In the spray-dried cases, the protein solubility (PS) of BWP was much greater than that of commercial soy protein isolates (SPI) at below pH 5 and above pH 6 ( P < 0.05). At below pH 7, the PS of those BWPs by ultrasonic-assisted extraction was higher than that by mechanical extraction or by ultrasonic-assisted extraction and additional de-fatting treatment. The water holding capacity of those BWPs obtained by freeze-drying was also significantly higher than that by spray-drying ( P < 0.05). The fat adsorption capacity of freeze-dried BWPs was significantly higher than that of SPI and those spray-dried BWPs ( P < 0.05). The emulsifying activity index (EAI) of some spray-dried BWPs was higher than that of SPI at below pH 4 and above pH 6, while the emulsion stability index (ESI) was lower than that of SPI at below pH 7 ( P < 0.05). The de-fatting pretreatment could improve the EAI and ESI of BWP, especially at above pH 6. In simulated gastric fluid, the digestion pattern of BWP was evidently different from that of SPI. In the pepsin digestion, the % N release was affected by the processing. The BWPs with low lipid contents had higher % N release as compared to those with high lipid contents. These results suggested that the functional properties and in vitro digestibility of BWP be associated with its lipid and ash contents, which could be affected by processing. Thus, functional and nutritional BWPs, potential for food applications, can be produced through controlling the processing.

Commercial Soy Protein Ingredients as Isoflavone Sources for Functional Foods

The knowledge of the contents and profile of isoflavones present in soy protein ingredients, as well as the effect of industrial processing, is important for the development of functional foods rich in these compounds. The results obtained here showed that the total isoflavone content varied significantly among products. For defatted and whole soy flours the total isoflavone content ranged from 120 to 340 mg/100 g, for soy protein isolates from 88 to 164 mg/100 g, and for commercial textured soy proteins, from 66 to 183 mg/100 g (wet basis, expressed as aglycones). The highest isoflavone content was found for soy hypocotyl flours, from 542 to 851 mg/100 g. Compared to hypocotyl and whole and defatted flours, soy ingredients presented a decrease of malonylglycosides and deesterified beta-glycosides with a significant increase in the percentage of aglycones, mainly for soy fibers (65-76%). While defatting was shown to cause isoflavone concentration without altering conjugation, extrusion process caused destruction of isoflavones and a significant increase in the amount of acetylglycosides, but this effect was less intense for the concentrates. From the results obtained it can be concluded that differences in isoflavone concentration and profile may be related to oscillations in the isoflavone content present in the raw material and to the type of processing.

Dielectric properties of soybean protein isolate dispersions as a function of concentration, temperature and pH

Dielectric properties of commercial soy protein isolate (SPI) dispersions were measured over the frequency range of 200–2500 MHz by the open-ended coaxial probe method using a network analyzer as a function of concentration (5, 10 and 15 g/100 g water), temperature (20–90 °C) and pH (4.5, 6.6 and 10). Results indicated that the dielectric constant ( ε′) decreased with temperature (except at 90 °C) and frequency while increased with concentration. The loss factor ( ε″) increased with frequency and concentration; however, temperature showed mixed effect. Both ε′ and ε″ data were related to frequency using a polynomial model. The significant change in ε′ and ε″ at 90 °C was a result of protein denaturation which was identified by differential scanning calorimetry (DSC). Change in the association/dissociation behavior of SPI dispersions due to electrostatic attraction/repulsion among protein molecules on heating as a function of pH was assumed to be responsible for the significant increase in dielectric parameters. Penetration depth ( D p) was estimated under various conditions and it decreased with an increase in frequency, concentration, temperature and pH. The minimum D p was found at alkaline pH at a temperature of 90 °C and frequency of 2450 MHz.

Effect of limited hydrolysis of soy protein on the interactions with polysaccharides at the air–water interface

The objective of the work was to study the effect of limited hydrolysis of soy protein on the interactions with polysaccharides with and without surface activity at the air–water interface at neutral pH where a limited incompatibility between macromolecules can occur. The surface pressure and phase angle as a function of time were evaluated with a drop tensiometer at 20 °C, pH 7 and ionic strength 0.05 M. Hydrolysates of 2% (H1) and 5.4% (H2) degree of hydrolysis (DH) with neutral protease from Aspergillus oryzae were obtained from a commercial soy protein isolate. The polysaccharides used were: hydroxypropylmethylcellulose (HPMC) as surface active polysaccharide; lambda carrageenan ( λC) and locust bean gum (LB) as non-surface active polysaccharides. It was found that increasing DH decreased the surface pressure and increased film viscoelasticity (determined as the phase angle, θ) of soy protein hydrolysates and the nature of protein–polysaccharide interactions was strongly affected by DH. The presence of polysaccharides led to an increase of surface pressure of H1 but when added to H2, HPMC and λC decreased the surface pressure. The less hydrolyzed protein H1 gave rise to a higher surface pressure and film viscoelasticity in combination with the polysaccharides. This result points out that a limited protein hydrolysis was sufficient to improve the surface properties of soy proteins if used in combination with polysaccharides. Polysaccharides used in admixture with hydrolyzed soy proteins could control and improve the stability of foams and emulsions not only by increasing bulk viscosity but also by improving film viscoelasticity.

Extraction, purification and characterization of globulin from common buckwheat (Fagopyrum esculentum Moench) seeds

Salt-soluble globulin was extracted from common buckwheat (Fagopyrum esculentum Moench) seeds. The protein content of buckwheat globulin (BWG) was over 90%. Anion-exchange chromatography (with stepwise salt gradient elution) was used to obtain two fractions of BWG, corresponding to the basic and acidic polypeptides, respectively, at a ratio of approximately 1:2. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the acidic and basic polypeptides were linked by disulfide bonds. The basic polypeptide has an estimated molecular weight of 23–25 kDa, an isoelectric point in slightly alkaline region (pH 8–9), and showed a high degree of homology with other legumin-like proteins. Disulfide and sulfhydryl contents in BWG were estimated as 36.4 and 3.20 μM/g of protein, respectively. BWG exhibited beneficial functional properties such as high solubility, emulsifying activity and emulsion stability, while the foaming properties were relatively poor. BWG had lower water holding capacity and comparable fat binding capacity when compared to a commercial soy protein product.

Thermorheological Characteristics of Soybean Protein Isolate

ABSTRACT: Small amplitude oscillation shear measurement was used to study gel rigidity of commercial soy protein isolate (SPI) dispersions during isothermal and non-isothermal heating. Temperature sweep data (20°C to 90°C atheating rate of 1°C/min) of SPI dispersions demonstrated that elastic modulus (G) predominates over viscous component (G′) for all concentrations studied. The gelation kinetics of SPI was evaluated by a non-isothermal technique as a function of elastic modulus (G). During experiments, it was observed that a critical concentration of 10% was required to form a true SPI gel. Thermorheological data of 10% and 15% SPI dispersions were adequately fitted by 2nd-order reaction kinetics. The reaction order of gelation was initially calculated by multiple regression technique correlating dG'/dt, G’and temperature, which finally was verified by linear regression of kinetic equation at selected order. Isothermal data of 15% SPI was also followed by 2nd-order reaction kinetics. The activation energy during the isothermal technique was significantly higher than non-isothermal gelation of SPI at same concentration level. Gel strength of the non-isothermally heated SPI sample (15% to 20%) was compared with isothermally heated (90°C for 30 min) one. Higher protein concentration (20%) and isothermal heating exhibited significantly higher gel rigidity while the difference between the 2 processes was insignificant at 15% concentration at a similar condition.

Effect of soy spent flakes and carbon black co-filler in rubber composites

Abstract The rubber composites that are reinforced by a mixture of soy spent flakes (SSF) and carbon black (CB) are investigated in terms of their viscoelastic properties. Soy spent flakes is a plentiful renewable material from the waste stream of commercial soy protein extraction. SSF contains mostly soy carbohydrate and dry SSF increases rubber modulus significantly. The aqueous dispersions of SSF and CB were first mixed and then blended with styrene–butadiene latex to form rubber composites by freeze-drying and compression molding method. The mixtures of SSF and CB at three different ratios are investigated as co-fillers. A 30% co-filler reinforced composite exhibits about 100 times increase in the shear elastic modulus compared with unfilled SB rubber, showing a significant reinforcement effect by the co-filler. Compared with the SSF composites, the recovery behaviors of the co-filler composites after the eight consecutive deformation cycles of dynamic strain are improved and are similar to that of the CB composites. The comparison of viscoelastic properties of the composites prepared by freeze-drying and casting methods indicates the composites prepared by freeze-drying method have a lower elastic modulus, but have a better recovery behavior due to its polymer mediated filler network structure. The co-filler composites with 50–75% substitution of CB by SSF have a greater elastic modulus than the CB reinforced composites.