Structural insights into fatty acid-driven enhancement of digestive resistance in high-amylose maize starch-lipid...

This study evaluated how fatty acid (FA) addition level, chain length, and unsaturation modulate resistant starch (RS) formation in high-amylose maize starch-fatty acid (HAMS-FA) complexes. HAMS was complexed with seven FAs, including saturated FAs with different chain lengths (C10:0-C18:0) and unsaturated C18 FAs (C18:1 and C18:2), at 15% and 20% addition levels. Systematic structural and physicochemical analyses, including complexation index (CI), FTIR, solid-state ¹³C NMR, X-ray diffraction, SEM/AFM, and DSC, were conducted to link multi-scale structural features with in vitro digestibility. Increasing FA addition from 15% to 20% caused only limited changes in CI, relative crystallinity, and RS content, suggesting that HAMS-FA complexation approached a near-saturation state at the 15% addition level. In contrast, FA molecular structure exerted a more pronounced influence on complex formation and digestive resistance. Medium-chain saturated FAs, especially myristic acid (C14:0), showed the highest CI, V-type crystallinity, and RS content, indicating that an appropriate chain length favored amylose-FA inclusion and stabilized V-type crystalline structures. Unsaturated FAs, particularly linoleic acid (C18:2), maintained relatively high RS content despite lower crystallinity, possibly due to steric effects associated with their bent molecular configurations, which may reduce enzyme accessibility. FTIR and solid-state ¹³C NMR supported non-covalent interactions and FA encapsulation within amylose helices, while SEM and AFM revealed denser and smoother surfaces after complexation. DSC further confirmed the presence of thermally stable Form II structures in HAMS-FA complexes. Overall, these findings indicate that RS formation in HAMS-FA systems is jointly regulated by complexation degree, V-type crystalline organization, surface compactness, thermal stability, and FA molecular geometry. This study provides structural insights for the rational design of starch-lipid complexes as potential low-glycemic food ingredients.