Corn zein undergoes conformational changes to higher β-sheet content during its self-assembly in an increasingly hydrophilic solvent

Viscoelasticity of corn zein is associated with the formation of beta-sheet secondary structures; however, studies of the fundamentals of this conformational change are limited due to zein insolubility and poor analytical resolution. Here, changes in soluble zein conformation were evaluated as the protein self-assembles in increasingly hydrophilic solvents to the concentration just before aggregation and precipitation. Circular dichroism spectra of zein showed that alpha-helix structures decrease in favor of random coil and beta-sheets with increases in water content in an ethanol-water system, similar to observations of zein when it becomes viscoelastic in dough systems. This was further supported by changes in Thioflavin T fluorescence emission spectra and intrinsic viscosity measurements. Two widely recognized molecular models for alpha-zein (hairpin and superhelical conformations) were tested at 75 and 45% ethanol concentration using molecular dynamics simulation for agreement with experimental results. Increase in solvent hydrophilicity increased beta-sheets and reduced distance between backbone anomeric carbons only for hairpin model, suggesting it to be the more valid of the two. These findings emphasize the importance of transformation to beta-sheets during zein self-assembly and provide further insight into the mechanisms by which the protein is functionalized into viscoelastic systems. (C) 2020 Published by Elsevier B.V.