Phytate negatively influences wheat dough and bread characteristics by interfering with cross-linking of glutenin molecules

Authors: PARK, EUN-YOUNG - Washington State University; FUERST, E - Washington State University; Baik, Byung-Kee

Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2016
Publication Date: 6/21/2016
Publication URL: http://handle.nal.usda.gov/10113/63351
Citation: Park, E., Fuerst, E.P., Baik, B.-K. 2016. Phytate negatively influences wheat dough and bread characteristics by interfering with cross-linking of glutenin molecules. Journal of Cereal Science. 70:199-206.

Interpretive Summary: Phytate is a strongly negatively charged molecule that behaves as an anti-nutrient in humans and animals by chelating minerals and making them unavailable for absorption. At the same time, phytate is receiving increased attention due to their ability to act as potent antioxidants by inhibiting iron-catalyzed hydroxyl radical formation and suppressing lipid peroxidation. Whole grain wheat is composed of approximately 1 to 2% phytate which is primarily located in the aleurone layer. Phytate could form complexes with protein molecules during dough mixing through ionic and multivalent cation-mediated interactions, resulting in delayed gluten development. Considering the fact that bran is responsible for the weakened dough strength and reduced bread quality of whole grain wheat flour, and phytate is primarily localized in the bran, phytate is suspected to be at least partially responsible for the impaired dough properties and poor bread baking quality of whole wheat flour. To identify the potential impact of phytate on the reduced bread baking quality of whole grain wheat bread, three different sources of phytate (including two chemical preparations and one extracted from wheat bran) were added to refined wheat flour at a 1% level; changes in dough mixing and physical properties, bread making quality, and interactions of glutenin molecules in dough and bread were determined. Phytate addition exhibited deleterious influences on dough mixing properties and bread baking quality with delayed dough development and decreased loaf volume of bread. Phytate addition decreased the proportions of polymerized glutenin proteins and high molecular weight glutenin molecules in gluten, which explains the resulting weakened gluten and dough strengths. Phytate may prevent oxidative cross links between glutenin molecules during dough mixing by their iron chelating-mediated antioxidant activity. It appears that phytate in whole grain wheat flour take part in delaying gluten development and producing incompletely developed gluten and dough networks, which result in a decreased bread loaf volume. The results from this study indicate that the selection of wheat varieties low in grain phytate content, along with the breakdown or elimination of phytate through processing, would be helpful for enhancing the bread baking quality of whole grain wheat flour.

Technical Abstract: The influence of added phytate on dough properties and bread baking quality was studied to determine the role of phytate in the impaired functional properties of whole grain wheat flour for baking bread. Phytate addition to refined flour at a 1% level substantially increased mixograph mixing time, generally increased mixograph water absorption, and reduced the SDS-unextractable glutenin polymer content of dough before and after fermentation as well as the loaf volume of bread. The added phytate also shifted unextractable glutenins toward a lower molecular weight form and increased the iron-chelating activity of dough. It appears that phytate negatively affects gluten development and loaf volume by chelating iron and/or binding glutenins, and consequently interfering with the oxidative cross-linking of glutenin molecules during dough mixing. Phytate could be at least partially responsible for the weak gluten network and decreased loaf volume of whole wheat flour bread as compared to refined flour bread.