Evolution of wheat gliadins conformation during film formation: A Fourier transform infrared study

The secondary structures of wheat gliadins (a major storage protein fractio n from gluten) in film-forming solutions and their evolution during film fo rmation were investigated by Fourier transform infrared spectroscopy. In th e film-forming solution, wheat gliadins presented a mixture of different se condary structures, with an important contribution of beta -turns induced b y proline residues. The presence of plasticizer did not have any influence on protein secondary structure in the film-forming solution. The evolution of protein conformation was followed during drying; the major feature of th is evolution was a clear growing of the infrared band at 1622 cm(-1), chara cteristic of intermolecular hydrogen-bonded beta -sheets. This revealed the formation of protein aggregates during film drying. The influence of the d rying temperature on film properties and gliadin secondary structures was a lso investigated. Higher drying temperatures induced an increase of both th e tensile strength of the films and the amount of beta -sheets aggregates. Although the appearance of heat-induced disulfide bridge cross-links has al ready been described, there is clear evidence that hydrogen-bonded beta -sh eets aggregates are also induced by thermal treatment. It was not possible, however, to determine whether there is a direct relationship between the o ccurrence of these aggregates and the increase of the tensile strength of t he films.