ORIGINAL ABSTRACT

The objective of this study was to determine if the pre-harvest glyphosate application time affects the chemistry of wheat starch. Glyphosate was sprayed at the ripe stage (recommended) and the soft dough stage (early application) of hard red spring wheat. Wheat kernel samples were collected before application and every 3 days until harvest, after which different starch characteristics were analyzed. The results indicate that glyphosate timing does not impact the spatial distribution or morphology of starch granules, as well as the percentage or molecular weight of amylose and amylopectin. However, thermal characteristics of wheat starch, especially when glyphosate was applied at the soft dough stage, showed significant differences. A decrease in the average amylopectin chain length and differences in the proportion of short-, medium-, and long-chain amylopectin was also observed. Overall, this study shows that the pre-harvest application of glyphosate can affect wheat starch chemistry, especially if applied earlier than recommended. PRACTICAL APPLICATIONS: Glyphosate is the most commonly used herbicide in the world, and it is sometimes used pre-harvest during wheat cultivation. The recommended time of application is 7 days prior to harvest when the crops are in the ripe stage of physiological maturity. However, some crops may not be at this stage during application due to non-uniform maturation in the field. The goal of this work was to determine the effect of glyphosate application time (recommended/ripe stage vs. early/soft dough stage) on wheat starch chemistry. The results show that the starch chain length characteristics and thermal behavior are impacted, especially if applied early. Thus, this study shows the importance of timely application to avoid effects on starch chemical properties, which in return could impact starch functionality in food systems. This information is critical in the field of agriculture and to our knowledge this study is one of the first in this area.