A multidimensional view on zein proteins: Structure and functionality in dough and bread systems

Sadat, Azin
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University of Guelph

This thesis examines the structure and functionality of zein in bakery products. Particular emphasis was laid on the optimization and application of vibrational and luminescence spectroscopy techniques to study complex zein and gluten dough systems. In this context, the molecular and sub-molecular structure of zein-gluten dough systems was investigated by fluorescence, Fourier transform (FT)-Raman, and Fourier transform infrared (FTIR) spectroscopy as well as confocal Raman microscopy (CRM). Formation of β-sheet-rich fibrils in zein dough was derived from the FTIR and FT-Raman protein secondary structure analyses, and the extrinsic Thioflavin T fluorescent probe results. In addition, the Raman scatter data reported on the dominant β-sheet type and the ratio of fully solvent-exposed and buried tyrosine residues in the zein and gluten network structures. Small and large deformation rheological behavior of the zein-gluten dough samples revealed that in addition to differences in protein structural units, weaker starch-protein interactions also contribute to the lower elasticity of zein dough compared with gluten dough. However, zein-rich dough samples showed high extensibility and resistance to extension, which were attributed to the formation of highly structured (β-sheet rich) fibrils as observed using cryo-scanning electron microscopy (Cryo-SEM) and CRM. Based on the gathered insights, a model was proposed for zein structure in a viscoelastic dough system. The in-depth information on the zein dough structure led to the development of gluten-free breads made with zein. The effect of addition of different hydrocolloids (hydroxypropyl methylcellulose (HPMC), guar and xanthan gum) and the inclusion of pregelatinized starch on zein dough and bread properties was examined. Small amplitude oscillatory and creep-recovery tests showed a notable increase in the viscous nature of the zein dough by addition of HPMC, likely due to the lubricating effect of HPMC on the zein fibrils. SEM images also revealed a continuous (foam-like) fine network structure of zein strands in the zein dough made with HPMC, presumably responsible for the higher specific volume of the bread. Therefore, this research has advanced the understanding of zein structure and functionality in bakery systems and provides a sound basis for the development of zein-based gluten-free breads.

Spectroscopy, Zein, Gluten, Bread