The effects of exogenous spermidine on starch development, multi-scale structure, and in vitro digestibility in wheat were investigated under drought stress

Spermidine (Spd) is a naturally occurring polyamine widely present in cereal grains. Despite its well-documented physiological activity in stress responses, whether Spd can directly regulate the multi-scale structure and digestive properties of wheat starch under drought conditions remains unclear. Therefore, this study applied drought stress (DR) during the early grain filling stage (1–10 days after anthesis), combined with exogenous spermidine spraying and spermidine inhibitor (Mitoguazone, MGBG), to investigate the effects of Spd on wheat starch formation, accumulation, multi-scale structure, and in vitro digestibility under DR treatment. The results showed that exogenous Spd enhanced starch synthase activity under DR treatment, promoted starch development and accumulation, and thereby increased wheat yield. Additionally, Spd increased the proportion of B-type starch granules, solubility, and swelling power under DR conditions. By reducing the proportion of long branched-chains, Spd decreased starch crystallinity and ordered structure, leading to lower gelatinization enthalpy and gelatinization temperature, while increasing the contents of rapidly digestible starch (RDS) and resistant starch (RS). In contrast, MGBG exhibited the opposite trends. This study reveals a novel function of polyamine compounds as starch structure modifiers, providing a chemical perspective for the quality regulation of food raw materials.