Effects of L-glutamic acid on wheat starch structure and functionality: multiscale characterization and molecular...

L-Glutamic acid (L-Glu) is central to carbon-nitrogen metabolism, yet its ability to improve starch quality by regulating grain metabolism and by directly modulating starch structure remains unclear. In this study, we integrated a field experiment with an in vitro experiment and combined untargeted metabolomics, microscopy, structural characterization, physicochemical and processing property analyses, and molecular dynamics simulations. It was found that under drought, L-Glu spraying reprogrammed the grain metabolome, with pathway enrichment in aminoacyl-tRNA biosynthesis and starch/sucrose metabolism. In vitro, L-Glu increased the full width at half maximum of the Raman band at 480 cm^-1 and altered the FTIR absorbance ratio of 1047/1022 cm^-1. L-Glu enhanced in vitro digestibility and reduced swelling power and paste transparency, while decreasing setback viscosity, suggesting a potential inhibition of short-term starch retrogradation; however, freeze-thaw stability was reduced. Microscopy revealed a more disordered gel network after L-Glu addition. Simulations showed that L-Glu formed 1.47-2.18 persistent hydrogen bonds with amylose chain per system and extensive hydrogen bonds with water.