Adsorption of alpha-, beta-, gamma- and omega-gliadins onto hydrophobic surfaces

Adsorption onto hydrophobic surfaces of alpha-, beta-, gamma-, and omega-gl iadins from the wheat variety Chinese Spring was studied by means of in sit u ellipsometry. Most measurements were conducted in 0.01 M phosphate buffer , pH 6.0, with the protein concentrations 1, 5 and 25 mu g/mL. The adsorbed amount varied between 1.3 and 11.4 mg/m(2), which is high considering the low protein concentrations. The concentration dependence was largest for th e alpha-gliadins and lowest for the omega-gliadins. An intermediate concent ration dependence was found for the beta- and gamma-gliadins, which also be haved similarly in all experiments. It was suggested that alpha-gliadins ag gregated at the surface to a larger extent than the other gliadins when the protein concentration was 25 mu g/mL. Further, it seemed as beta- and gamm a-gliadins switched from a side-on orientation (major axis parallel to the surface) to an end-on orientation (major axis perpendicular to the surface) with increasing concentration, contrasting to the omega-gliadins that prob ably had side-on orientation at all concentrations. Sequential adsorption m easurements indicated that alpha-, beta-, and gamma-gliadins blocked adsorp tion of omega-gliadins, but could replace omega-gliadins in a previously fo rmed layer. (C) 1999 Academic Press.