Functional Properties Of Soy Protein Isolates Research Articles

Effect of Mono- and Polysaccharide on the Structure and Property of Soy Protein Isolate during Maillard Reaction.

As a protein extracted from soybeans, soy protein isolate (SPI) may undergo the Maillard reaction (MR) with co-existing saccharides during the processing of soy-containing foods, potentially altering its structural and functional properties. This work aimed to investigate the effect of mono- and polysaccharides on the structure and functional properties of SPI during MR. The study found that compared to oat β-glucan, the reaction rate between SPI and D-galactose was faster, leading to a higher degree of glycosylation in the SPI-galactose conjugate. D-galactose and oat β-glucan showed different influences on the secondary structure of SPI and the microenvironment of its hydrophobic amino acids. These structural variations subsequently impact a variety of the properties of the SPI conjugates. The SPI-galactose conjugate exhibited superior solubility, surface hydrophobicity, and viscosity. Meanwhile, the SPI-galactose conjugate possessed better emulsifying stability, capability to produce foam, and stability of foam than the SPI-β-glucan conjugate. Interestingly, the SPI-β-glucan conjugate, despite its lower viscosity, showed stronger hypoglycemic activity, potentially due to the inherent activity of oat β-glucan. The SPI-galactose conjugate exhibited superior antioxidant properties due to its higher content of hydroxyl groups on its molecules. These results showed that the type of saccharides had significant influences on the SPI during MR.

Physicochemical and functional property of the Maillard reaction products of soy protein isolate with L-arabinose/D-galactose.

Soy protein isolate (SPI) is widely used in the food industry because of its nutritional and functional properties. During food processing and storage, the interaction with co-existing sugars can cause changes in the structural and functional properties of SPI. In this study, SPI-l-arabinose conjugate (SPI:Ara) and SPI-d-galactose conjugate (SPI:Gal) were prepared using Maillard reaction (MR), and the effects of five-carbon/six-carbon sugars on the structural information and function of SPI were compared. MR unfolded and stretched the SPI, changing its ordered conformation into disorder. Lysine and arginine of SPI were bonded with the carbonyl group of sugar. The MR between SPI and l-arabinose has a higher degree of glycosylation compared to d-galactose. MR of SPI enhanced its solubility, emulsifying property and foaming property. Compared with SPI:Ara, SPI:Gal exhibited better aforementioned properties. The functionalities of amphiphilic SPI were enhanced by MR, SPI:Gal possessed better hypoglycemic effect, fat binding capacity and bile acid binding ability than SPI:Ara. MR endowed SPI with enhanced biological activities, SPI:Ara showed higher antioxidant activities, and SPI:Gal exhibited stronger antibacterial activities. Our work revealed that l-arabinose/d-galactose exhibited different effects on the structural information of SPI, and further affected its physicochemical and functional property. © 2023 Society of Chemical Industry.

Modification of soy protein isolate using dielectric barrier discharge cold plasma assisted by modified atmosphere packaging

In this study, soy protein isolate (SPI) was treated by modified atmosphere packaging (MAP) assisted dielectric barrier discharge (DBD) cold plasma (CP) to improve its functional properties. For this reason, SPI powders were treated with DBD-CP at the oxygen ratio of 20 %, 30 %, 40 %, 50 % and 60 %, respectively. The results showed that with the increase of oxygen content, the structure of SPI was destroyed, protein macromolecule depolymerized. However, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed that the primary structure of SPI was not disrupted. In addition, when the oxygen content was greater than 40 %, the solubility, water holding capacity, gelling, emulsifying and foaming properties of SPI were significantly improved (p < 0.05). The results showed that high-oxygen packaging can increase the active particles generated during processing, thereby optimizing the structural and functional properties of SPI. Therefore, MAP can serve as a more efficient method for DBD-CP to modify soybean protein.

Comparison of hydrodynamic and ultrasonic cavitation effects on soy protein isolate functionality

In this study, soy protein isolate (SPI) dispersions (3%, w/v) were treated with hydrodynamic cavitation (HC) with a venturi tube (treatment volume: 2 L) and ultrasonic cavitation (UC) (treatment volume: 200 mL and 2 L) under the power of 550 W for 5, 10, 20, and 30 min. The effects of HC and UC treatment on the physicochemical and functional properties of SPI were investigated, and the results were compared to better evaluate the HC effects on food proteins. The results showed that the electrophoretic profile and pH were not affected by UC or HC treatment. The particle size and viscosity of SPI were reduced after UC or HC treatment. Both UC and HC treatment significantly (P < 0.05) increased the surface hydrophobicity. UC treatment at the volume of 2 L did not alter the exposed or total sulfhydryl content; however, UC treatment at the volume of 200 mL and HC treatment altered the exposed sulfhydryl content and decreased the total sulfhydryl content. Moreover, the solubility, emulsifying activity index, emulsion stability index, and foaming capacity were also significantly (P < 0.05) improved; however, foam stability was reduced after UC and HC treatment. Under the conditions investigated in this study, the effect of HC treatment on the physicochemical and functional properties of SPI was more pronounced than that of UC treatment at the volume of 2 L, and was similar to that of UC treatment at the volume of 200 mL. These results suggest that HC could be an effective method to improve the functional properties of food proteins.

Emulsifying and Foaming Properties of Soy Protein Isolates with Covalent Modification by (-)-Epigallocatechin-3-Gallate

Soy Protein Isolates (SPI) with covalent modification by (-)-Epigallocatechin-3-Gallate (EGCG) were prepared under the alkaline condition. The effects of covalent modification on the emulsifying and foaming properties of SPI were evaluated. The Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) profiles of the modified SPI revealed that EGCG treatment caused cross-linking of subunits. Emulsifying activity of modified SPI significantly increased when compared with that of control (p<0.05) at the concentration of 35 mg/mL. Modification of SPI by EGCG caused a decrease in the foam volume initially. In the range of 15 to 35 mg/mL, the foaming activities of modified SPI were found to be less than those of the control (p<0.05). The foaming stabilities of modified SPI were significantly higher when compared to those of control (p<0.05). The results obtained in this study indicated the modification by EGCG resulted in the enhancement of emulsifying activity and foaming stability of SPI. This modification may serve as a promising approach for improving functional properties of SPI.

Preparation and functional properties of protein from heat-denatured soybean meal assisted by steam flash-explosion with dilute acid soaking

The combined pretreatment of heat-denatured soybean meal using steam flash-explosion (SFE) with sulfuric-acid soaking was investigated to prepare protein from soybean meal. When soybean meal was pretreated by SFE at 1.8MPa, 2.2MPa for 8min and at 2.0MPa for 8min and 10min, combined with 0.9% sulfuric-acid soaking, the extraction yield of protein increased to 67.72%, 70.54%, 69.47% and 71.21% respectively, compared to untreated soybean meal. Scanning electron micrograph of pretreated samples showed the structural disruption of soybean meal. After pretreatment, the protein yield was improved, while protein content of soy protein isolate (SPI) decreased slightly. The functional properties of SPI from pretreated soybean meal were all improved compared to untreated soybean meal and the relationship between functional properties and the changes of surface hydrophobicity of SPI was discussed. The emulsification properties and fat-binding capacity of pretreated SPI were superior to those of SPI prepared from white flakes.

Characterization of complexes of soy protein and chitosan heated at low pH

The objective of this research is to investigate the complex of soy protein isolate (SPI) and chitosan (CS) heated (121 °C, 15 min) at low pH. The formation and functional properties of heated SPI–CS complex were investigated by electrophoresis, Fourier transform infrared spectroscopy (FTIR), solubility, ζ-potential and emulsifying property. The results indicated that the heated SPI–CS complex is probably more like a soluble SPI–CS aggregate which is driven by electrostatic interaction. Heated SPI–CS complex exhibited improved solubility than SPI (less than 10%) and unheated SPI–CS mixture (about 50%) at pH 4.0 because of the increased electrostatic repulsion (ζ-potential) after heat treatment. The effects of mixing ratios, molecular weights (MW) and charge densities (CD) of chitosan on the stability of heated SPI–CS complex showed the influence was mainly dependent on mixing ratios and CD of chitosan. Concomitantly, the emulsifying activity index of SPI at pH 4.0 was significantly improved by heated complexation and the emulsion stability index was not affected. Additionally, the heated SPI and/or SPI–CS complex exhibited slightly decreased pepsin and trypsin digestibility. The results suggested that the physicochemical and functional properties of SPI could be modulated by heated complexing with chitosan, using appropriate mixing ratio, MW and CD of chitosan.

EFFECTS OF DRYING METHOD ON PHYSICOCHEMICAL AND FUNCTIONAL PROPERTIES OF SOY PROTEIN ISOLATES

Three soy protein isolates (SPIs) were obtained by different drying methods, including freeze-drying, spray-drying and vacuum-drying. These SPIs were found to be significantly different in color of CIELAB L*, a*, b*values, enthalpies of denaturation (ΔH) in differential scanning calorimetry, 1-anilino-8-napthalene-sulfonate surface hydrophobicities and total sulfhydryl group contents (P < 0.05). The solubility of spray-dried SPI was significantly higher than that of freeze-dried SPI and vacuum-dried SPI (P < 0.05), except at pH 4–5. Spray-dried SPI had much lower turbidity, higher solubility, and better emulsifying and foaming properties than freeze-dried and vacuum-dried SPIs. These results suggested that drying methods could influence the functional properties of SPIs. PRACTICAL APPLICATIONS The utilization of soy protein isolates (SPIs) in various foods is based on their highly desirable functional properties such as solubility, emulsification and foaming. These functional properties may be affected by different drying methods such as freeze-drying, spray-drying and vacuum-drying. This study explains the effects of drying methods on the physicochemical and functional properties of SPIs, which is useful for SPI researchers and manufacturers. Additionally, freeze-drying is usually used in laboratory experiments, while spray-drying is utilized in industrial processes and vacuum-drying is applied in both cases. Hence, the research results on functional properties of freeze-dried SPI in laboratory experiments may not have practical applicability. The direct evidence of the effects of various drying methods on the functional properties of SPIs is based on experiments using the same drying method that is consistent with industrial practice. It is very important that the drying method must be taken into consideration in the research of the functional properties of soy proteins.