Divergent and shared gut microbiota responses to repeated intervention with structurally distinct pectic...

This study investigated how gut microbiota responds to repeated interventions with two structurally distinct pectic polysaccharides (ALRP3 and USRP2) isolated from red raspberries and how structural variations influence fermentation outcomes. The low-molecular-weight and less branched ALRP3 was rapidly fermentable, while high-molecular-weight and more branched USRP2 was slowly fermentable. Both pectic polysaccharides modulated gut microbiota and promoted SCFA levels, and these effects were significantly influenced by polysaccharide structure, dosing cycles, and their interaction. During fed-batch fermentation, the substrates were initially added at 0 h and subsequently supplemented at 12, 24, and 36 h, resulting in four substrate additions in total. Following repeated supplementation, the fecal microbiota gradually formed new stable community structures, and SCFAs steadily accumulated, with both pectic polysaccharides reaching the peak total SCFA production after the third supplementation. They enriched similar beneficial bacteria but also induced distinct flora. ALRP3 specifically boosted butyrate-producing bacteria and butyrate production, while USRP2 enriched specific Bifidobacterium strains. These results support the targeted design of pectic polysaccharide-based microbiota regulation strategies.