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 °C, which is above its glass transition temperature (Tg), changes in its secondary structure suggested that the protein loses its native structure, mainly composed of α-helices (∼68%), and a viscoelastic system is formed by a structural rearrangement that favors β-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 β-sheet structures (from ∼48% to ∼28% after the first 3 min) 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 β-sheet structures (∼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 β-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.