Effects of pre-harvest glyphosate use on protein composition and shikimic acid accumulation in spring wheat

Authors: MALALGODA, MANEKA - North Dakota State University; Ohm, Jae-Bom; HOWATT, KIRK - North Dakota State University; SIMSEK, SENAY - North Dakota State University; GREEN, ANDREW - North Dakota State University

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2020
Publication Date: 6/27/2020
Citation: Malalgoda, M., Ohm, J., Howatt, K., Simsek, S., Green, A. 2020. Effects of pre-harvest glyphosate use on protein composition and shikimic acid accumulation in spring wheat. Food Chemistry. 332:127422. https://doi.org/10.1016/j.foodchem.2020.127422.
DOI: https://doi.org/10.1016/j.foodchem.2020.127422

Interpretive Summary: Glyphosate-based herbicide is sometimes used as a harvest aid to promote uniform crop maturation and timely harvest. Functional property of gluten proteins in grain is very important since it is highly associated with wheat processing and end-product quality. However, no report was available on the effect of application of glyphosate-based herbicide on functional property of gluten proteins for hard red spring wheat. The goal of this study was to determine the effect of application timing of a glyphosate-based herbicide on the properties of gluten proteins in hard red spring wheat. In this experiment, a glyphosate-based harvest aid was sprayed to wheat plant at the two grain development stages, soft dough (early application) and the ripe (recommended application) stages in green house. Upon harvest, wheat grain samples were analyzed for protein properties. The results indicated that the glyphosate-based herbicide application did not impact the protein characteristics such as amino acid composition, secondary structure and gluten protein composition. However, glyphosate-based herbicide application decreased the molecular size of proteins, when applied at the soft dough stage. This indicates that application of the harvest aid can cause significant degradation of the functional properties of gluten proteins by affecting the molecular size of proteins in grain. The information obtained from this experiment will be a very valuable reference to determining the application time of glyphosate-based herbicides to maintain functional properties of gluten proteins as well as to promote timely harvest for hard red spring wheat.

Technical Abstract: Harvest aids are used to promote uniform crop maturation and timely harvest. During wheat cultivation, harvest aids are recommended to be applied at least a week prior to harvest during the ripe stage of physiological maturity. However, some grains may not be at this stage due to non-uniform maturation. In this context, the goal of this study was to determine the effect of harvest aid timing on the chemistry of wheat gluten proteins and shikimic acid accumulation. A greenhouse study was conducted where a glyphosate based harvest aid was sprayed at the soft dough (early application) and the ripe stage (recommended stage) to wheat cultivar ‘Glenn’. For the control samples, water was sprayed instead of glyphosate at the same developmental stages. Samples were collected prior to spraying and every three days until harvest. Whole wheat flour samples were then analyzed for amino acid composition, secondary protein structure, gluten protein composition and molecular weight as well as shikimic acid accumulation. The results of the study indicated that harvest aid application does not impact the amino acid composition, protein secondary structure and gluten protein composition. However, harvest aid application decreased the molecular weight of SDS extractable and unextractable proteins, and significantly increased the amount of shikimic acid accumulation, especially when applied at the soft dough stage. Thus, this study indicates that harvest aids can cause significant differences in the physicochemical and functional properties of wheat gluten proteins by affecting the molecular weight of proteins, while significantly increasing the shikimic acid content in affected plants.