Multiscale structure and digestibility of ultrasound-extrusion prepared starch-phenolic complex

This study investigated the preparation of V-type starch-phenolic acid complexes via ultrasound-assisted extrusion, utilizing three distinct starch sources (corn, potato, and pea) and two phenolic acids (ferulic acid, FA; gallic acid, GA). Structurally, the complexation was significantly influenced by the starch botanical source; corn starch-phenolic complexes demonstrated higher relative crystallinity (RC) and short-range molecular order compared to their potato and pea starch counterparts. Furthermore, starch-GA complexes outperformed their FA systems, exhibiting significantly higher complex indices, enhanced RC (peaking at 11.44% for corn starch-GA), and greater short-range order. Functionally, these improvements in complexation efficiency, crystallinity, and short-range order-driven by both the starch botanical source and the phenolic acid type-were associated with superior enzymatic resistance. The corn starch-GA complex (UECG) achieved the lowest overall digestibility, with significantly reduced rapidly digestible starch (RDS, 30.14%) and elevated resistant starch (RS, 48.38%) levels. Microstructural observations indicated the development of compact nanoparticle architectures capable of selectively resisting enzymatic attack, resulting in heterogeneous surface erosion of the particles after digestion. These structural features support a proposed mechanism wherein the complexes arrange into protective structures. These findings highlight how the interplay between starch botanical source and ligand structure synergistically influences complex architecture, providing a scalable pathway for developing digestion-resistant ingredients.