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

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.