Milk β-lactoglobulin complexes with tea polyphenols.

Area of Science:

• Food Chemistry
• Biochemistry
• Molecular Interactions

Background:

• The impact of milk on tea polyphenol antioxidant activity is not fully understood.
• Complexation between milk proteins and tea polyphenols can modify both antioxidant capacity and protein structure.

Purpose of the Study:

• To investigate the molecular-level interactions between beta-lactoglobulin (β-LG) and key tea polyphenols: catechin (C), epicatechin (EC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG).
• To determine the binding mode, binding constants, and the effects of polyphenol complexation on β-LG stability and secondary structure.

Main Methods:

• Fourier-transform infrared (FTIR) spectroscopy
• Circular dichroism (CD) spectroscopy
• Fluorescence spectroscopy
• Molecular modelling

Main Results:

• Polyphenols bind to β-LG through hydrophilic and hydrophobic interactions, with binding constants ranging from 2.2×10^3 M⁻¹ to 1.3×10^4 M⁻¹.
• The number of bound polyphenols per β-LG molecule varied between 0.9 and 1.3, depending on the specific polyphenol.
• Polyphenol complexation altered β-LG conformation, increasing β-sheet and α-helix content, indicating enhanced protein structural stabilization.

Conclusions:

• Tea polyphenols interact with β-LG, forming complexes via a combination of hydrophilic and hydrophobic forces.
• The binding of polyphenols stabilizes the β-LG structure, affecting its secondary conformation.
• These findings elucidate the molecular mechanisms underlying the modification of tea polyphenol antioxidant activity upon milk addition.