How do the hydroxyl group number and position of polyphenols affect the foaming properties of ovalbumin?

In order to explore the effect of polyphenol structure on the foaming properties of protein, the ovalbumin-polyphenol (OVA-polyphenol) complexes were developed by combining OVA with gallic acid (GA), 3,4-dihy-droxybenzoic acid (DA), P-hydroxybenzoic acid (PA), 4-coumaric acid (CA), trans-3-hydroxycinnamic acid (T3A) and trans-2-hydroxycinnamic acid (T2A), respectively, and then the foaming properties, binding in-teractions, physicochemical properties and protein structure of complexes were determined. Results showed that the foaming ability (FA) and surface hydrophobicity were in the order of OVA-PA > OVA-T2A > OVA-DA > OVA-CA > OVA-T3A > OVA-GA > OVA, whereas the alpha-helix, fluorescence quenching ability and zeta-potential of OVA-polyphenol complexes followed an opposite trend, suggesting that fewer hydroxyl groups and ortho-aromatic structures were positively associated with higher foaming properties of the complexes. Physicochem-ical properties revealed that OVA-polyphenol complexes obtained higher zeta-potential and surface hydrophobicity, revealing that the addition of polyphenol promoted the adsorption and rearrangement of OVA in liquid-gas interface and increased its foaming properties. Molecular interactions demonstrated that PA, due to their fewer hydroxyl binding sites, and T2A, due to the existence of competitive binding, led to the instability of OVA-polyphenol complexes, promoting the movement of OVA and the exposure of its hydrophobic groups, thus contributing to the conversion of alpha-helix to the random coil conformations and ultimately promoting the FA of the complexes. In conclusion, polyphenols could increase the foaming properties of OVA, and PA retained the highest priority due to its excellent overall performance. These findings will be of interest for developing foods with improved functional properties.