Interaction Between α-Gliadin Layers

The interaction between layers of α-gliadin has been studied by the surface force technique. The protein was both deposited according to the Langmuir–Blodgett technique and adsorbed onto hydrophilic mica surfaces. Deposition was performed at surface pressures of 10 and 20 mN/m, and contact angle measurements of the hydrophobic films indicated a more homogenous layer at the higher surface pressure. Atomic force microscopy images showed no significant differences between surfaces deposited at the two surface pressures. From the surface force measurements, the contact separation indicated a layer thickness of 65 Å. The long range forces between deposited gliadin layers in the presence of 1·0 and 0·1 mmsodium chloride weredominated by electrostatic repulsion, and the absence of long-range steric forces suggested that the molecules in the protein film adopt a very compact conformation. Some adhesive force was obtained upon decompression. The interaction between α-gliadin layers adsorbed from ethanol solution, and measured in the presence of sodium chloride aqueous solution, was dominated by steric forces. From AFM measurements, the adsorbed film was markedly rougher than the deposited film, but displayed degree of shorter-range order.