Soy Protein Isolate Emulsions Research Articles

Physicochemical properties of soy protein isolate gels emulsified with various oils using a microbial transglutaminase

Soy protein isolate (SPI) gels emulsified with oils including soybean, olive, palm, and eicosapentaenoic acid (EPA) were prepared by a microbial transglutaminase (MTGase). The hardness of 10% SPI gel was greatly increased by adding higher amount of oils. The emulsion gels prepared with 10% SPI and 30% olive oil showed the highest hardness of 1,711 g. In the gelation with various oil content (5–30%), the higher concentration of oils indicated the drastic increase of elastic modulus G′ and viscous modulus G″ during initial gelation for 7 min. The G′ value of SPI emulsion gel showed the 150 (soybean oil 30%), 147 (olive oil 30%), 121 (palm oil 30%), and 61 Pa (EPA 25%), respectively. In the color value of SPI emulsion gel, addition of higher concentration of oils resulted in the increase of L value (brightness), indicating 99.14 (L value) at 30% palm oil. The micro-structure of SPI emulsion gel entrapped with various oils showed the homogeneous network with small porosity compared with that of SPI gel without oil. In particular, SPI emulsion gel with 10% palm oil showed the compact structure distributed evenly with small porosity. Conclusively, the functional and rheological properties of SPI emulsion gel produced by catalytic action of MTGase could be modulated by the type and content of oils fortified.

Cold, gel-like soy protein emulsions by microfluidization: Emulsion characteristics, rheological and microstructural properties, and gelling mechanism

In this paper we reported the rheological and microstructural properties of a kind of novel cold, gel-like soy protein isolate (SPI) emulsions obtained by means of microfluidization. These gel-like emulsions were formed from untreated and preheated (95 °C, 15 min) SPI at a protein concentration of 6% (w/v), and various oil volume fractions (Φ; 0.2–0.6) and NaCl concentrations (0–500 mM). The rheological properties and microstructure were characterized using steady viscosity and dynamic oscillatory measurements, as well as confocal laser scanning microscopy (CLSM). The characteristics (e.g. droplet size distribution and creaming stability) of the emulsions, formed at lower protein concentrations (e.g. 0.5–4.0%), were also characterized, aiming to reveal the mechanism of the gel-like network formation. The dynamic oscillatory data indicated that both untreated and preheated SPI emulsions exhibited gel-like rheological properties, but the specific apparent viscosity (η) and storage modulus (G′) of the latter ones were much higher at a comparable Φ. Both η and G′ progressively increased upon Φ increasing, indicating enhanced inter-droplet interactions. At a given Φ value (0.3), increasing NaCl concentration progressively increased η and G′ of the preheated SPI emulsions, indicating the importance of electrostatic screening for the gel-like network formation. The CLSM analyses confirmed formation of the gel-like network, mainly composed of aggregated oil droplets, which was closely dependent on the Φ and NaCl concentration. The gel-like network was formed by bridging flocculation of oil droplets, mainly through inter-droplet hydrophobic interactions between the proteins adsorbed at the interface. These results suggested that soy proteins exhibit excellent potential to produce cold, gel-like emulsions, especially through a heat pretreatment followed by microfluidization, which might be of vital importance for the development of soy protein-based formulations, especially as carriers for heat-labile ingredients with health effects.

Stability and Physical Properties of Emulsions Prepared with and without Soy Proteins

The ability of emulsifiers (gum arabic, starch and soy protein isolate (SPI)) and texture modifiers (gum tragacanth and carrageenan) alone and as a mixture with SPI to stabilize oil-in-water emulsions at high oil concentrations was studied. Parameters investigated included droplet size distribution, color (DE), viscosity and creaming stability. At 10% (w/v) emulsifier to oil ratio, emulsions stabilized with gum arabic, starch and SPI had average oil droplet sizes lower than 1µm. Increasing the oil content by two-fold (emulsifier/oil ratio of 10:20), increased the average droplet size of the gum arabic and SPI emulsions to 1.5 and 4.2 mm, respectively, while that of the starch emulsion remained unchanged. At 5% oil concentration, gum tragacanth and carrageenan stabilized emulsions yielded two average droplet sizes of 0.5 µm (52.7%) and 1.8 µm (46.5%), and 0.5 µm (48.8%) and 1.7 µm (46.6%), respectively. Increasing the oil concentration to 10% increased the particle size with fairly similar proportions. Gum arabic stabilized emulsions had lower DE than starch and SPI (except at 20% oil content). DE of carrageenan and tragacanth emulsion decreased significantly when used as a mixture with SPI. Droplet size strongly affected color. All concentrated emulsions exhibited shear-thinning behavior irrespective of oil, emulsifier type and concentration. SPI, followed by starch and gum arabic emulsions showed good stabilities over the 15 days storage period. Gum tragacanth and carrageenan emulsion stabilities were only improved when combined with SPI, particularly at 5% oil concentration.

Effect of Ultrasonic Treatment on the Graft Reaction between Soy Protein Isolate and Gum Acacia and on the Physicochemical Properties of Conjugates

Soy protein isolate (SPI) was grafted with gum acacia (GA) in this work. In comparison with classical heating at high water activity, ultrasound could accelerate the graft reaction between SPI and GA. A degree of graft (DG) of 34 was obtained by ultrasonic treatment for 60 min, whereas 48 h was required with classical heating. Ultrasonic treatment improved the concentration of available free amino groups of SPI. The grafted SPI showed significantly (p < 0.05) higher levels of emulsifying activity index, emulsifying stability index, and surface hydrophobicity than native SPI. The droplet size (D[3,2] and D[4,3]) of SPI emulsion decreased from 8.3 to 2.3 microm and from 25.7 to 7.1 microm through ultrasound-assisted grafting, respectively. Moreover, SPI-GA conjugates gave emulsions exhibiting more stability against creaming than those prepared with only SPI during ambient temperature storage (20 days). Decreases of lysine and arginine contents during the graft reaction indicated that these two amino acid residues attended the covalent linkage between SPI and GA. The results of secondary structure suggested that grafted SPI had decreased alpha-helix and beta-sheet levels and increased unordered coils level.

Effects of different oils on the properties of soy protein isolate emulsions and gels

Abstract The emulsion properties, protein adsorption and visco-elastic properties of heat-treated soy protein isolate (SPI) emulsions containing sunflower oil, soy oil and palm stearin were studied at neutral pH. The rheological properties, textural profile and fat adsorption capacity of subsequently induced glucono-δ-lactone (GDL) gels were investigated. At neutral pH the palm stearin emulsions showed higher stability than the sunflower and soy oil emulsions. The former also showed higher protein adsorption, emulsifying activity index and visco-elastic properties than the latter, indicating a higher denaturation degree for SPI at the oil/water interface of palm stearin emulsions at neutral pH. Acidified SPI-palm stearin emulsion gels were significantly harder than the soy and sunflower oil versions as well as the control (SPI without oil), whereas gels containing the two liquid oils were softer than the control. SPI-palm stearin gels also had higher fat adsorption capacity than SPI-sunflower oil/soy oil emulsion gels.

High pressure versus heat treatments for pasteurisation and sterilisation of model emulsions

Heat treatments can have considerable influence on the droplet size distribution of oil-in-water emulsions. In the present study, high-pressure (HP) pasteurisation and sterilisation were evaluated as alternatives for heat preservation of emulsions. HP conditions used were 600 MPa, 5 min, room temperature and 800 MPa, 5 min, 80 °C initial temperature, 115 °C maximum temperature for HP pasteurisation and HP sterilisation respectively. The effects on droplet size of these conditions were compared to heat treatments for whey protein isolate (WPI) and soy protein isolate (SPI) emulsions at two pH values and two ionic strengths. For WPI, also the effect of protein in the bulk phase was evaluated. Both HP and heat pasteurisation treatments resulted in similar or slightly decreased average droplet sizes compared to the untreated samples. For neutral SPI emulsions, heat sterilisation increased the average droplet size from 1.6 μm to 43.7 μm, while HP sterilisation resulted only in a small increase towards an average droplet size of 2.1 μm. The neutral WPI emulsions, except those with a high ionic strength, gave similar results with respect to the droplet size, showing that for neutral pH WPI or SPI emulsions HP sterilisation is preferable above heat sterilisation. Concerning the low pH WPI emulsions, the droplet sizes were unaffected after both heat and HP sterilisation. Heat pasteurisation and sterilisation are effective treatments to preserve food products that are based on emulsions with respect to microbial safety. However, heat treatments can negatively affect emulsion stability. Currently, in addition to high pressure at room temperature, high-pressure treatments at elevated temperature received a great deal of interest to achieve sterilised products. This study evaluated the effects of both heat and high-pressure pasteurisation and sterilisation on droplet size of whey protein isolate and soy protein isolate emulsions. It was shown that for pasteurisation treatments, both heat and high pressure have minor effects on the droplet size of the emulsion. However, for sterilisation purposes high-pressure treatment is preferable for emulsion at neutral pH. High-pressure sterilisation can therefore be interesting alternatives to heat treatments to preserve emulsion stability.

Characteristics of Sodium Caseinate‐ and Soy Protein Isolate‐Stabilized Emulsion‐Gels Formed by Microbial Transglutaminase

ABSTRACT: Protein‐stabilized emulsion gels were prepared via microbial transglutaminase (mTGase) catalysis, and their physicochemical characteristics were examined. Emulsion oil droplet size and interfacial protein load were measured. The sodium caseinate and soy protein isolate emulsion gels exhibited different microstructures and physical properties. The emulsion gels improved the storage stability of aroma compounds. Rheological measurements of the emulsion gels revealed interesting strength, gelation kinetics, and thermal sensitivity properties. The mTGase‐induced emulsion gels comprised a fine network which led to less release of aroma compounds upon storage than did emulsions. These results suggest that emulsion gels may be used to improve the texture of food emulsions and to control release of food aromas.

Effect of polysaccharides on textural characteristics of soy protein isolate emulsion.

Effect of polysaccharides on textural characteristics of soy protein isolate emulsion.