9 Gluten proteins at interfaces.

J. ORNEBRO (1), A.-C. Eliasson (1), and T. Nylander (2). (1) Dept. of Food Technology, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE- 221 00 Lund, Sweden; (2) Dept. of Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.

We have investigated the interfacial behaviour of gliadin fractions (alpha-, beta-, gamma- and omega- gliadins), the high molecular weight glutenin subunit 1Dx5 and the 58 kD central repetitive domain from the subunit. The methods employed were ellipsometry, surface film balance and the surface force technique. Adsorption of gliadins to a hydrophobic surface showed that the variation in adsorbed amount with bulk concentration was largest for the alpha-gliadins and least for the omega-gliadins. The beta- and gamma- gliadins behaved similarly in all experiments. It is likely that the omega-gliadins adsorbed with the long axis parallel to the surface (side-on) for all the investigated concentrations, whereas the other gliadin fractions changed from a side-on orientation at low concentration to an orientation with the long axis normal to the surface at high concentration. Aggregation may have influenced the adsorption at high concentration, especially for the alpha-gliadins. Adsorption of subunit 1Dx5 and the 58kD peptide gave much higher adsorbed amounts for subunit 1Dx5. The subunit was also highly sensitive to the ionic strength, whereas the 58 kD domain was unaffected. We suggest that the non-repetitive domain(s) are crucial for the formation of a dense layer; both for gliadins and for subunit 1Dx5. Surface tension measurements displayed a higher surface pressure for subunit 1Dx5 than for the 58 kD peptide. Measurements with the surface force technique on subunit 1Dx5 deposited on muscovite mica indicated the presence of a steric repulsive force. This force can prevent coalescence of foams and emulsions.