Covalent modification of soy protein isolates by hydroxytyrosol: Effects on structural and functional properties of adducts

The effect of covalent binding of different concentrations of hydroxytyrosol (HT) to soy protein isolate (SPI) by enzymatic method on the structure and function of the complex was investigated. Polyphenol binding rate increased and then decreased with increasing hydroxytyrosol concentration, with a maximum binding rate of 38.10 ± 1.08%. Covalent binding to HT resulted in a significant increase in the turbidity of the adduct and a significant decrease in the free sulfhydryl content and surface hydrophobicity. The structure of the adduct was altered and the α-helix structure was converted to a β-sheet one. The maximum foaming property of the adducts was observed at a HT concentration of 40 μmol/g, which was 28.84% higher than the control SPI. The adduct had maximum solubility (52.84 ± 0.18%) at HT concentration of 50 μmol/g. The emulsifying properties of the adducts were maximized at a hydroxytyrosol concentration of 60 μmol/g. When the HT concentration was 70 μmol/g, the DPPH and ABTS radical scavenging rates of the adducts were increased by 245.03% and 26.35%, respectively, compared with the control SPI.