Stabilization of apo α-lactalbumin by binding of epigallocatechin-3-gallate: Experimental and molecular dynamics study.

α-Lactalbumin (ALA) is a Ca2+-binding protein which constitutes up to 20% of whey protein. At acidic pH, and in the apo-state at elevated temperatures, ALA is the classic 'molten globule' (MG). This study examined epigallocatechin-3-gallate (EGCG) binding to ALA in its apo form (apoALA) and stabilizing effect on protein structure thereof. EGCG binds to apoALA in both native and MG state. The complex of EGCG and ALA is more stable to thermal denaturation. The docking analysis and molecular dynamic simulation (MDS) showed that Ca2+ removal decreased conformational stability of ALA, because of the local destabilization of Ca2+-binding region. EGCG binding to apoALA increases its stability by reverting of conformation and stability of Ca2+-binding region. Therefore, EGCG-induced thermal stability of apoALA is based on increased apoALA conformational rigidity. This study implies that during gastric digestion of tea with milk EGCG would remain bound to ALA, albeit in the Ca2+-free form.

Antioxidative capacity and binding affinity of the complex of green tea catechin and beta-lactoglobulin glycated by the Maillard reaction.

Major green tea catechin, epigallocatechin-3-gallate (EGCG), binds non-covalently to numerous dietary proteins, including beta-lactoglobulin of cow's milk. The effects of glycation of proteins via Maillard reaction on the binding capacity for polyphenols and the antiradical properties of the formed complexes have not been studied previously. Binding constant of BLG glycated by milk sugar lactose to EGCG was measured by the method of fluorophore quenching. Binding of EGCG was confirmed by CD and FTIR. The antioxidative properties of the complexes were examined by measuring ABTS radical scavenging capacity, superoxide anion scavenging capacity and total reducing power assay. Glycation of BLG does not significantly influence the binding constant of EGCG for the protein. Conformational changes were observed for both native and glycated BLG upon complexation with EGCG. Masking effect of polyphenol complexation on the antioxidative potential of the protein was of the similar degree for both glycated BLG and native BLG.

Macromolecular crowding conditions enhance glycation and oxidation of whey proteins in ultrasound-induced Maillard reaction.

High intensity ultrasound (HIUS) can promote Maillard reaction (MR). Macromolecular crowding conditions accelerate reactions and stabilise protein structure. The aim of this study was to investigate if combined application of ultrasound and macromolecular crowding can improve efficiency of MR. The presence of crowding agent (polyethylene glycol) significantly increased ultrasound-induced whey protein (WP) glycation by arabinose. An increase in glycation efficiency results only in slight change of WP structure. Macromolecular crowding intensifies oxidative modifications of WP, as well as formation of amyloid-like structures by enhancement of MR. Solubility at different pH, thermal stability and antioxidative capacity of glycated WP were increased, especially in the presence of crowding agent, compared to sonicated nonglycated proteins. The application of HIUS under crowding conditions can be a new approach for enhancement of reactions in general, enabling short processing time and mild conditions, while preserving protein structure and minimising protein aggregation.