Abstract
The effects of sodium alginate (SA) and pH value on the formation, structural properties, microscopic morphology, and physicochemical properties of soybean protein isolate (SPI)/SA microparticles were investigated. The results of ζ-potential and free sulfhydryl (SH) content showed electrostatic interactions between SPI and SA, which promoted the conversion of free SH into disulfide bonds within the protein. The surface hydrophobicity, fluorescence spectra, and Fourier transform infrared spectroscopy data suggested that the secondary structure and microenvironment of the internal hydrophobic groups of the protein in the SPI/SA microparticles were changed. Compared with SPI microparticles, the surface of SPI/SA microparticles was smoother, the degree of collapse was reduced, and the thermal stability was improved. In addition, under the condition of pH 9.0, the average particle size of SPI/SA microparticles was only 15.92 ± 0.66 μm, and the distribution was uniform. Rheological tests indicated that SA significantly increased the apparent viscosity of SPI/SA microparticles at pH 9.0. The maximum protein solubility (67.32%), foaming ability (91.53 ± 1.12%), and emulsion activity (200.29 ± 3.38 m2/g) of SPI/SA microparticles occurred at pH 9.0. The application of SPI/SA microparticles as ingredients in high-protein foods is expected to be of great significance in the food industry.
Highlights
Soy protein isolate (SPI) has good nutritional value, can provide a proper balance of various essential amino acids for human health, and can be used as a good source of protein supplement for vegans [1]
The pH value had a significant influence on the conformation and physicochemical properties of the SPI/Sodium alginate (SA) microparticles
The electrostatic and hydrophobic interactions between SPI and SA promoted the conversion of free SH groups in the protein to intermolecular disulfide bonds
Summary
Soy protein isolate (SPI) has good nutritional value, can provide a proper balance of various essential amino acids for human health, and can be used as a good source of protein supplement for vegans [1]. Its physicochemical properties are affected by the surrounding environmental conditions compared to animal proteins, which limits its food processing applications [2]. Previous studies have indicated that the preparation of microparticles could improve the internal structural properties and microscopic morphology of the protein, and have favorable effects on the stability, emulsifying, and foaming properties [3,6]. The microparticulated whey proteins prepared by [8] in the low-acidic pH range exhibited substantially higher particle size reduction than at neutral pH, with improved solubility and emulsifying properties. Complexation with polysaccharides can improve the viscosity, solubility, and emulsifying properties [11]. The effect of pH on the interaction mechanism and physicochemical properties of proteins and polysaccharides during the formation of microparticles need to be further clarified. The formation mechanism, structural properties, particle morphology, and physicochemical properties of SPI/SA microparticles were studied. The results provide the theoretical foundation and technical support for the application of SPI/SA microparticles in food systems as a new generation of functional food ingredients
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