Aggregative and structural properties of wheat gluten during post-harvest maturation

Wheat post-harvest maturation induced baking and technological quality improvement through a series of biochemical and colloidal changes. Weak-, middle-, and strong-gluten wheat displayed varying gluten network structures that determined the flour ingredient formulations and processing conditions. However, the aggregation and structural properties of wheat with different gluten strengths post-harvest remain largely unexplored. In this study, we investigated changes in the aggregative properties of gluten protein, gluten composition, S-S content, network structure, and secondary structures of weak-, middle-, and strong-gluten wheat during postharvest maturation. The results indicated that the macromolecular aggregation of gluten proteins was impaired in weak-gluten wheat, while it was enhanced for middle- and strong-gluten wheat during storage. Postharvest maturation resulted in an increase in glutenin content and a decline in the gliadin and gliadin/glutenin ratio in middle- and strong-gluten wheat as well as a decreased glutenin content in weak-gluten wheat. Moreover, additional gluten subunits were observed in middle- and strong-gluten wheat, but no substantial change was observed in weak-gluten wheat with long storage times. The disulfide bond content of gluten protein for middle-gluten and strong-gluten gradually increased but declined for weak-gluten wheat. Secondary structure analysis of gluten indicated that post-harvest maturation caused the conversion of alpha-helix to random coil for weak-gluten wheat, 8-turn and random coil to alpha-helix for middle-gluten wheat, and 8-turns to alpha-helix for stronggluten wheat, which led to a disordered structure for weak gluten and an ordered stable gluten network for middle- and strong-gluten. Thus, the increased S-S and alpha-helix content induced by post-harvest maturation enhanced the aggregation of gluten proteins for middle- and strong-gluten wheat, resulting in a denser network structure. Conversely, the decrease in the content of alpha-helix resulted in the existence of a looser gluten network structure for weak-gluten wheat during post-harvest maturation.