Adsorption of protein fractions from wheat onto methylated silica surfaces

The kinetics of the sequential adsorption of gliadins and water-soluble fraction (WSF) from the wheat variety Kosack onto hydrophobic silica (methylated silica) surfaces were studied by in situ ellipsometry. The measurements were made in water and in 0.01M acetate buffer, pH 4.0 and 5.0, with and without 0.1M NaCl. The concentration of gliadins and WSF was 1.7 µg/ml. The adsorption of gliadins in water was investigated at three different protein concentrations (0.17, 1.7, and 17 µg/ml), and the adsorption was found to be very high with regard to the low concentrations of protein in solution. The results of the sequential adsorption in water indicated that the WSF adsorbed to preadsorbed gliadins. When proteins of the WSF were adsorbed first, they blocked further adsorption of gliadins. Measurements in acetate buffer at different pH values showed that the effect of pH was larger in the experiments where the gliadins were adsorbed first, both for the initial adsorption and for the sequential addition of WSF. An increase in ionic strength also increased the amount of WSF adsorbed to preadsorbed gliadins. These results indicate that the sequential adsorption of WSF to gliadins is strongly affected by electrostatic interactions.