Surface rearrangement of adsorbed EGCG-mucin complexes on hydrophilic surfaces.

The kinetic adsorption-desorption behaviour of porcine gastric mucin in the presence of physiologically relevant concentrations of the polyphenol epigallocatechin gallate (EGCG) was investigated using high-resolution kinetic optical waveguide lightmode spectroscopy (OWLS) and atomic force microscopy (AFM). Comparison with dynamic light scattering results from EGCG-mucin mixtures indicates that discrete particles are formed whose size increases with increasing EGCG:mucin ratio. These particles are deduced to be the adsorbing entities, which fuse on the surface to form complex surface layers. At low molar EGCG:mucin ratios (<∼1000), aggregates fuse on the surface to form a monolayer similar to one of pure mucin. With increasing EGCG concentration, the surface assembly of aggregates becomes consistent with their rearrangement and spreading in the shape of a spherical segment. At the highest molar ratios investigated (>12,000) the particles begin to destabilize. The presence of EGCG leads to birefringence hysteresis during adsorption-desorption, indicating structural rearrangement, even at molar ratios ∼1000. The intensification of the phenomenon with increasing EGCG:mucin ratio mimics what was previously observed with the increase of mucin concentration in an EGCG-free system.