Heat-Induced Aggregation of a Globular Egg-White Protein in Aqueous Solution: Investigation by Atomic Force Microscope Imaging and Surface Force Mapping Modalities

Abstract

Aqueous solution conditions have been chosen so that a globular gelling food protein, ovalbumin, is adsorbed on a molecularly smooth muscovite mica surface. Atomic force microscope (AFM) fluid-tapping and electrical double layer imaging modes and force mapping have been used to characterize the heat-induced aggregation mechanism and surface properties of the protein. At a solution concentration of 0.5 μg/mL, single globular structures, which were consistent with the dimensions of ovalbumin monomers, were observed with the fluid-tapping imaging mode. Heat treatment caused protein aggregation and produced larger globular structures. At a solution concentration of 20 μg/mL, a protein film was formed and the electrical double layer mode of imaging revealed that the heat-induced globular aggregates were more heterogeneous than the native protein. The heterogeneity of the heat-treated ovalbumin film was also apparent from the effective film thickness maps derived from the force data obtained on approach of the ...