From Phosphorus Nutrition to Starch Functionality: Effects of Phosphorus Fertilization on Sorghum Starch Biosynthesis, Multiscale Structure, and Processing Properties

Phosphorus fertilization can regulate starch accumulation and quality in cereal grains, but its effects on sorghum starch remain insufficiently understood. This study investigated sorghum cultivar Liaoza 82 under four phosphorus levels: 0, 40, 80, and 160 kg P2O5 ha−1. Phosphorus application significantly affected starch accumulation and the activities of starch biosynthesis-related enzymes, including AGPase, GBSS, SSS, and SBE. Moderate phosphorus, particularly 80 kg P2O5 ha−1, increased amylose content, granule size, molecular weight, amylopectin branching degree, and medium-to-long amylopectin chains, whereas the highest phosphorus treatment weakened these effects and caused granule surface depressions. Although the A-type crystalline pattern was unchanged, phosphorus modified crystallinity, short-range order, thermal properties, solubility, swelling power, and pasting behavior. Within the phosphorus range investigated, P2 produced a favorable combination of selected structural and thermal characteristics, including lower crystalline order and lower gelatinization temperature and enthalpy, whereas some pasting parameters were highest under P3. These findings indicate that phosphorus fertilization alters sorghum starch structure and functionality, with the response depending on the specific starch characteristic evaluated.