Similarities and differences in secondary structure of viscoelastic polymers of maize α-zein and wheat gluten proteins

The secondary structure of a dough-like zein polymer was compared to the structure present in a wheat viscoelastic system using FT-IR spectroscopy. When zein was mixed at 35 degrees C, which is above its glass transition temperature (T-g), changes in its secondary structure suggested that the protein loses its native structure, mainly composed of alpha-helices (similar to 68%), and a viscoelastic system is formed by a structural rearrangement that favors beta-sheet structures. This rearrangement is very similar to the structural changes observed in gluten viscoelastic polymers. Upon removal of shear stress, the zein polymer showed a rapid decrease in the proportion of beta-sheet structures (from similar to 48% to similar to 28% after the first 3min) in favor of unordered structures. At the same time, the viscoelasticity of the polymer decreased rapidly. In contrast, gluten, in a similar viscoelastic system and held at the same temperature, showed a fairly constant high content of beta-sheet structures (similar to 49%) coinciding with the slow relaxation time typical of gluten networks after the removal of shear. We speculate that the addition of a protein capable of causing extensive and stable beta-sheet formation in the zein-starch viscoelastic polymer could increase the stability and relaxation time of the zein system and, thereby, create the possibility of a zein dough with similar functionality to a wheat viscoelastic system. (C) 2006 Elsevier Ltd. All rights reserved.