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BACKGROUND: Soy protein isolate (SPI) has promising applications in various food products because of its excellent functional properties and nutritional quality. The structural and emulsifying properties of covalently modified SPI by (−)‐epigallocatechin‐3‐gallate (EGCG) were investigated. RESULTS: SPI was covalently modified by EGCG under alkaline conditions. SDS‐PAGE analysis revealed that EGCG modification caused crosslinking of SPI proteins. Circular dichroism spectra demonstrated that the secondary structure of SPI proteins was changed by EGCG modification. In addition, the modifications resulted in the perturbation of the tertiary structure of SPI as evidenced by intrinsic fluorescence spectra and surface hydrophobicity measurements. Oil‐in‐water emulsions of modified SPI had smaller droplet sizes and better creaming stability compared to those from unmodified SPI. CONCLUSION: The covalent modification by EGCG improved the emulsifying property of SPI. This study therefore provided an innovative approach for improving the emulsifying properties of proteins. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract β-lactoglobulin (β-lg), the predominant protein in bovine whey, was chemically modified by (−)-epigallocatechin-3-gallate (EGCG) to develop a biomacromolecule with antioxidant activity. The EGCG-modified β-lg was characterized by SDS-PAGE, MALDI-TOF MS and intrinsic fluorescence spectroscopy. The antioxidant properties of EGCG-modified β-lg was assessed using DPPH radical scavenging activity, iron chelating ability, and inhibition of Cu2+-induced LDL oxidation. SDS-PAGE and MALDI-TOF MS results indicated the dimerization of β-lg after EGCG modification. Intrinsic fluorescence spectra suggested that EGCG modification caused an alteration in the conformational structure of β-lg. The results demonstrated that EGCG-modified β-lg possessed great antioxidant potential in terms of scavenging DPPH radical and chelating ferrous ion. Furthermore, the EGCG-modified β-lg showed a protective effect against LDL peroxidation. The results indicate that EGCG-modified β-lg could provide significant health benefits as an antioxidant. Highlights • Covalent modification by EGCG caused the formation of β-lg dimer. • EGCG modification altered β-lg conformation making it more hydrophilic. • EGCG-modified β-lg is a novel biomacromolecule with antioxidant activity. [ABSTRACT FROM AUTHOR]