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

摘要

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 (Tg), changes in its secondary structure suggested that the protein loses its native structure, mainly composed of alpha -helices (~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 ~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 beta -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 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..