Short-chain fatty acid and gut microbiota character following synergistic in vitro fermentation of resistant starch–dietary fiber complexes from tiger nuts

BACKGROUND The coexistence of non-starch polysaccharides and resistant starch (RS) impacts the physiological functions of dietary fiber, especially the availability of dietary fiber with some specific structures (e.g. insoluble dietary fiber, IDF). Therefore, three complexes with different ratios of RS/IDF from tiger nuts were prepared, followed by an investigation of their corresponding physicochemical and structural properties, as well as the regulatory role in gut microbiota. RESULTS The results indicated that the complex with RS/IDF ratio of 5/95 (H-IDF) had the greatest water retention, water swelling and oil retention capacities. All three complexes had a similar amylopectin/amylose ratio, which attenuated the impact on microbial fermentation. However, the complex with RS/IDF ratio of 40/60 (L-IDF) had the greatest potential to promote microbial fermentation demonstrated by severe morphological damage. Furthermore, the fermentation of L-IDF led to the greatest generation of acetate and butyrate, but the lowest generation of isobutyrate. Meanwhile, the fermentation of L-IDF enhanced Prevotella abundance, accompanied by a reduced Firmicutes/Bacteroidetes ratio and pathogenic bacteria in terms of Proteobacteria and Escherichia-Shigella . The increased butyrate levels during 24 h fermentation might be primarily due to the enhanced abundance of Faecalibacterium in the early phases and Bifidobacterium in the later phases. The further analysis of functional prediction consistently supported a significantly up-regulated carbohydrate metabolism and down-regulated amino acid metabolism following L-IDF fermentation. CONCLUSION This study might highlight a new approach for designing complex carbohydrates with targeted intestinal health functions via the regulation of the RS/IDF ratio. © 2026 Society of Chemical Industry.