Interactions between tea polyphenol and two kinds of typical egg white proteins—ovalbumin and lysozyme: Effect on the gastrointestinal digestion of both proteins in vitro

The promotion or inhibition of gastrointestinal digestion of tea polyphenol (TP) towards the two typical proteins from egg white (ovalbumin (OVA) and lysozyme (LYZ)) was examined. The results showed that TP made OVA/LYZ easier for digestion in the pepsin solution at pH 1.2 and inhibited OVA/LYZ digestion in pancreatin solution at pH 7.5. Non-covalent interactions between OVA/LYZ and TP and the secondary structure of OVA/LYZ were studied by using Fluorescence spectroscopy and Fourier transform infrared spectroscopy (FTIR), respectively. Results suggested that stronger conformational change occurred at pH 1.2 compared with that of pH 7.5 affected by TP in both proteins. Non-covalent interactions between OVA/LYZ and TP at pH 1.2 increased random and β-sheet structures in both proteins at the expense of α-helix, which resulted in the proteins with looser structures. At pH 7.5, an opposite second structural change of both proteins caused by the non-covalent interactions between OVA/LYZ and TP. The conformational and second structural change of proteins (substrate) might be a reason for promoting and inhibiting digestion of OVA/LYZ affected by TP.