Influence of Prolamin Composition on Mechanical Properties of Cast Wheat Gluten Films

The prolamin composition of gluten was shown to have a major influence on network viscoelasticity and on breadmaking quality, but its effect on films mechanical properties has never been investigated. Two glutens from different wheat varieties (NSA 2 and Farak) were compared. The prolamin composition of these glutens was quite different, Farak variety being richer in unextractable glutenins. These differences induced contrasting functional properties (alveographic analysis and mixing properties), featuring a strong (Farak) and a weak (NSA 2) gluten. Films were made by casting using several dispersing agents. The influence of protein composition due to genotype was very weak and was overwhelmed in all cases by the process influence. The weak influence of prolamin composition was further investigated by fractionating a commercial gluten into gliadin-rich and glutenin-rich fractions. Films were made from these fractions. Their mechanical properties revealed that, at similar composition, glutenin films were more resistent than gluten and gliadin films. However, a study of the plasticiser influence on films mechanical properties showed that these differences could be totally shielded by modifying the plasticiser amount in the film. Finally, it was possible to draw a logarithmic relationship between stress and strain, this relationship being convenient for the whole gluten as well as for the fractions.