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Conformational Change in the Structure of Wheat Proteins During Mixing in Hard and Soft Wheat Doughs

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Title: Conformational Change in the Structure of Wheat Proteins During Mixing in Hard and Soft Wheat Doughs
Author: Jazaeri, Sahar
Department: Department of Food Science
Program: Food Science
Advisor: Seetharaman, Koushik
Abstract: This thesis describes an investigation of the mechanistic differences of hard and soft wheat varieties in the course of dough formation. These two classes of wheat exhibit dissimilar end-use, as hard wheat flour is known for its bread making attributes, whereas soft wheat flour is suitable for cake and cookie production. This difference is related to the grain hardness, protein content and property of gluten, in addition to chemical interactions that are occurring during dough making. Covalent and hydrophobic interactions, as well as hydrogen bond formation, are the main interactions that take place during dough mixing. However, the contribution of each interaction in dough formation of hard and soft wheat is not known. One variety of hard and one variety of soft wheat flour were mixed to their optimum hydration level (500 BU), as determined by farinograph. The extent of covalent interactions of gluten proteins during dough mixing was examined by monitoring changes in the solubility of flour proteins in a 2% Sodium Dodecyl Sulfate (SDS) media. Moreover, the contribution of thiol groups to covalent bond was examined by measuring the changes in the accessible thiols throughout the mixing. Lower extractability of proteins and accessible thiols of hard wheat dough, compared to soft wheat dough, indicated the predominant role of covalent interactions in hard wheat dough. The complementary results from Size Exclusion High Performance Liquid Chromatography (SE-HPLC) indicated that covalent interaction of hard wheat dough primarily occurs between Low Molecular Weight (LMW) and High Molecular Weight (HMW) gluten proteins, whereas this interaction mainly occurs among LMW proteins in soft wheat doughs. Fewer hydrophobic interactions in hard wheat dough in compare with soft wheat measured by Front-face fluorescence spectroscopy indicated that this interaction is more dominant in soft wheat dough. Study of the conformational change in secondary structure of protein (indirect approach to monitor hydrogen bond) by fourier transform infrared (FTIR) spectroscopy showed that β-sheets are formed in both varieties at their optimum dough strength. In hard wheat dough this structure resulted mainly from disulfide linkages, whereas in soft wheat dough this structure is more likely the result of hydrophobic interactions.
Date: 2013-03
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