To Örebro University

Dietary fibres are key modulators of gut health, including barrier integrity and immune function, yet these effects are not sufficiently characterised. β-Glucans and rhamnogalacturonan-I (RG-I) have been shown to shape microbial composition and immune signalling, but their specific contributions to barrier integrity require further elucidation. Paper I examines how faecal fermentation supernatants (FS) from Pleurotus eryngii (PE) cultivated on distinct substrates influence intestinal barrier integrity in an LPS-stimulated Caco-2 model, revealing substrate-driven variations in tight junction modulation. Paper II describes the comparative effects of whole PE, its digested derivatives and a β-glucan-enriched extract on gut microbiota composition and metabolism in elderly individuals, using an in vitro fermentation model, highlighting the superior modulatory potential of the whole PE. Paper III explores the immunoregulatory properties of PE’s FS in an LPS-stimulated Caco-2 model, demonstrating their role in cytokine signal-ling and barrier’s protection. Paper IV evaluates the capacity of PE FS to mitigate bile acid-induced barrier dysfunction in in vitro and ex vivo colonic models, underscoring their protective effects against hyperpermeability. Paper V investigates the prebiotic potential of carrot RG-I in a human intervention study, showing its ability to enhance bifidobacteria populations, modulate immune responses and support barrier integrity. In conclusion, this thesis advances the understanding of dietary fibre bioactivities beyond conventional microbiota analyses. By demonstrating that β-glucans and RG-I modulate epithelial and immune functions alongside microbial interactions, it establishes a mechanistic foundation for precision nutrition strategies targeting gut health through an integrated, systems-based approach.