Digestion‐Stage Structural Evolution and In Vitro Colonic Fermentation of Intestinally Undigested Residues From Tiger Nut Starch‐Fatty Acid Complexes

Abstract

Starch‐fatty acid complexes can generate intestinally undigested material that subsequently enters colonic fermentation, but how this material evolves across gastrointestinal digestion and whether different tiger nut starch‐fatty acid systems show distinct fermentation responses remain unclear. In this study, native tiger nut starch (NTS) and complexes prepared with lauric acid (TS‐C12:0), palmitic acid (TS‐C16:0), and oleic acid (TS‐C18:1) were examined at the undigested, oral, gastric, and intestinal stages by SEM, XRD, and FTIR, followed by in vitro fecal fermentation of the intestinally undigested residues. NTS showed progressive morphological erosion across digestion, whereas the complex samples remained heterogeneous and retained V‐type‐like diffraction features to differing extents. In the pooled human fecal inoculum model, the blank produced substantial background SCFAs (1.295 mg/mL at 24 h). Total SCFA concentrations for NTS, TS‐C12:0, TS‐C16:0, and TS‐C18:1 were 1.904, 2.209, 2.087, and 2.120 mg/mL, respectively; only TS‐C12:0 differed significantly from NTS. FOS and the complex‐residue groups were associated with lower relative abundance of Escherichia‐Shigella than the blank and NTS, whereas Bifidobacterium differences were not significant. At the species level, Bifidobacterium longum and Bifidobacterium bifidum showed higher relative abundances in several substrate groups, whereas Dialister sp. Marseille‐P5638 was most abundant in the TS‐C18:1 group. LEfSe distinguished these substrate‐associated communities: TS‐C18:1 by a Negativicutes‐ Dialister lineage, TS‐C12:0 by Segatella , NTS by Bacteroides , and FOS by Bifidobacterium longum and Faecalibacterium , whereas TS‐C16:0 showed no discriminative taxon above the thresholds, and follow‐up tests confirmed the between‐group differences for the selected genera. PERMANOVA and ANOSIM did not support significant beta‐diversity separation. Within the scope of this pooled‐inoculum in vitro model, these findings describe stage‐dependent structural changes and substrate‐associated fermentation and compositional differences among the three systems tested; they do not establish a direct structure‐microbiota mechanism or generalize to individual human gut microbiota responses.