Physicochemical and Multiscale Structural Characterization of Sorghum Cultivars and Their Associations with Anti-Digestion Properties

Sorghum is recognized as a potential functional ingredient with high resistance to digestion. Therefore, this study investigates the anti-digestive properties of eight different types of sorghum cultivars with distinct compositional differences. The results confirmed that the whole sorghum flours exhibit stronger anti-digestive properties compared to its isolated starch, indicating that non-starch components play a role in inhibiting starch digestion. However, there was no significant correlation between the differences in individual components among sorghum varieties and their resistance to digestion. Analysis of sorghum starch structure demonstrated that relative crystallinity and double-helix degree in the long-range ordered architecture show a significant positive correlation with resistant starch (RS). Small-angle X-ray scattering (SAXS) revealed that the relatively thick and dense layered structure of sorghum starch is associated with a lower degree of enzymatic hydrolysis. Gel permeation chromatography (GPC) analysis showed that higher weight-average molecular weight is associated with a higher RS content to a certain extent, while a higher PDI is unfavorable for the formation of digestion-RS structures due to its association with a reduction in the onset gelatinization temperature. Cultivars AH-3, AH-5, and AH-2 with higher molecular weight, narrower molecular weight distribution and denser nanoscale lamellar structures exhibit superior digestion resistance. This research provides a reference for the screening of low-glycemic-index sorghum varieties and their application in functional foods.