Microwave fixation enhances gluten fibril formation in wheat endosperm

Authors: ORENDAY-ORTIZ, JOSE - Washington State University; Morris, Craig

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2018
Publication Date: 7/3/2018
Citation: Orenday-Ortiz, J.M., Morris, C.F. 2018. Microwave fixation enhances gluten fibril formation in wheat endosperm. Cereal Chemistry. 95:536-542. https://onlinelibrary.wiley.com/doi/abs/10.1002/cche.10057.
DOI: https://doi.org/10.1002/cche.10057

Interpretive Summary: Bread wheat is one of the most important crops in the world and possesses unique functional properties that allow it to produce an array of foodstuffs, most notably bread and other baked products. These properties are mainly attributed to a wheat doughs viscoelastic inherent nature caused by the hydration of seed storage proteins called prolamins. This group of proteins is comprised of monomeric gliadins and polymeric glutenins. Gliadins are soluble in aqueous alcohols and contribute to the extensibility of a dough, whereas glutenins are insoluble in aqueous alcohols and mainly confer a doughs elasticity, and together they form gluten. As wheat grains mature these proteins are deposited and accumulated in the endosperm to form a proteinaceous matrix. This matrix surrounds starch granules and is brought together upon flour hydration and dough mixing. Although the exact changes that occur during mixing are not completely understood, it is generally accepted that there is an exchange of disulphide bonds and protein-protein interactions within the gluten network. The aim of the present work was to assess the marked structural differences on the endosperm microstructure in wheat kernels treated with microwave and refrigeration conditions. SEM was used to characterize these physical structural differences. Identification of the microstructural characteristics of gluten proteins in the wheat endosperm provide an important foundation towards improving the performance of flours for end-use quality. In summary, use of microwave treatment for fixating wheat kernels for observation in microscopy applications enhances the formation of a fibrous gluten network. At the microscopic level, from this work, isolated proteinaceous matrix surrounding starch granules undergoes a morphological change from the excitation of microwaves to form gluten fibrils and these fibrils may change to a more continuous phase to form gluten sheets. In one aspect, if one wishes to study wheat kernel morphology without the presence of gluten protein artifacts then one may omit microwave treatment and choose to proceed with refrigeration fixation.

Technical Abstract: The wheat storage proteins, primarily glutenin and gliadin, contribute unique functional properties in food products and play a critical role in determining the end-use quality of wheat. In the wheat endosperm these proteins form a proteinaceous matrix deposited among starch granules only to be brought together to form a viscoelastic gluten network upon flour hydration. Although the genetics, molecular characterization, and biochemistry of these proteins have been heavily studied there remains a lack of knowledge in the precise structural formation of gluten outside of models. This study examined the effects of microwave and refrigeration fixation on the marked structural changes of wheat endosperm. Kernels subjected to microwave treatment were associated with the formation of gluten fibrils as observed by scanning electron microscopy. In kernels fixed at refrigeration temperature no fibrils were observed, indicating that the kinetics occurring during microwave treatment disrupted the native state stabilizing the proteinaceous matrix. As such, the enhancement of gluten fibril formation caused by microwave treatment may offer new opportunities to study the physical formation of gluten in wheat kernels.