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The structural evolution of gluten in refined and whole grain breads: A study of soft and hard wheat breads from flour to final product
J. E. BOCK (1), K. Seetharaman (2). (1) University of Guelph, Guelph, ON, Canada; (2) University of Minnesota, St. Paul, MN, U.S.A.

Recent work investigating gluten secondary structure in dough systems has provided tantalizing insights as to how small perturbations in gluten structure may impact bread quality. Specifically, shifts in gluten structure from β-turns to β-sheets in doughs with bran may be partially responsible for quality defects in whole grain bread. This study aimed to further that knowledge by monitoring gluten secondary structure in soft and hard wheat refined and whole grain bread at different stages during processing. Commercial hard red spring (HW) and soft red winter wheat (SW) flours were used to make breads with whole grain doughs created by substituting bran for 15% of the refined flour. ATR-FTIR spectra were collected from samples and analyzed for gluten secondary structural content. Freshly mixed doughs demonstrated the greatest β-sheet content (53-57%) compared to any other dough stage. Refined HW doughs demonstrated continual relaxation of β-sheets to β-turns through dough processing (-13% to panning), whereas relaxed SW doughs (-6 to 10%) partially reverted to sheets during punching and panning (1 to 3%).  The data also confirmed earlier findings that the presence of bran triggers the formation of additional β-sheets (4 to 5%) in both HW and SW doughs. Doughs with bran exhibited less structural relaxation (-3 to 6% β-sheets) during processing. Interestingly, HW doughs exhibited only 1-2% more β-turns and only 1-4% fewer β-sheets than SW doughs. Analysis of the bread during baking revealed that SW generates a larger sheets:turns ratio compared to HW in refined bread, 21.26 vs. 3.55, respectively, that grows to 129.04 vs. 5.28 on addition of bran. This suggests the ability of gluten to resist substantial secondary structural alteration during baking, specifically formation of excessive β-sheets, may be a key factor in high quality bread.

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