Unsaturated fatty acid structure governs hierarchical assembly and digestive properties of starch-lipid complexes.

The influence of unsaturated fatty acid molecular geometry on the assembly and digestive properties of starch-lipid complexes remains unclear. Here, five UFAs with distinct chain lengths and configurations were incorporated into gelatinized wheat starch via ultrasound-assisted dynamic high-pressure microfluidization to construct hierarchical complexes. Multiscale analyses showed that UFA geometry governed amylose helix inclusion, V-type crystallinity, and lamellar packing. Monounsaturated UFAs promoted compact ordered assemblies, whereas highly unsaturated UFAs generated looser interfacial structures. These differences were reflected in digestion behavior, with oleic-acid-based complexes exhibiting enhanced digestion resistance and delayed lipid release, while certain highly unsaturated systems such as DHA showed accelerated starch hydrolysis and fatty acid liberation. Notably the linoleic acid-based complex exhibited the highest resistant starch content of 20.77% and the slowest fatty acid release with 29.70% of fatty acids still retained after 120 min of digestion. Correlation analysis and molecular dynamics simulations further indicated that digestive resistance depends on the continuity of hierarchical packing rather than complexation efficiency alone. These findings clarify geometry-dependent structure-digestion relationships in starch-lipid complexes and support structure-guided design of systems with tunable digestive properties.