Structural differences in novel pectic polysaccharides from Rosa roxburghii tratt drive distinct gut microbiota profiles: Evidence from in vitro fecal fermentation

Rosa roxburghii Tratt fruits are rich in polysaccharides. Two novel polysaccharides, RRTP-1 and RRTP-2, were purified and characterized as pectin using HPLC, FTIR, GC-MS, and NMR analysis. RRTP-1 was primarily composed of homogalacturonan (HG), featuring a linear main chain with various branching structures including galactose, glucose, arabinose, and mannose residues. RRTP-2 was also a highly branched HG with significant contributions from galactose, rhamnose and arabinose. Compared to RRTP-2 (262.35 kDa, DE 22.03 %), RRTP-1 exhibited a lower molecular weight (179.05 kDa) and a higher degree of esterification (DE, 41.10 %). Both of them were efficiently utilized by gut microbes to produce butyric acid and lower pH. Their structural differences led to distinct gut microbiota composition. RRTP-1 selectively enriched Phocaeicola, Faecalibacterium, and Bifidobacterium, whereas RRTP-2 selectively enriched Limosilactobacillus, Lachnospira, and Coprococcus. Despite structure differences in RRTP-1 and RRTP-2, the keystone microbes and enzymes involved in their degradation exhibited similarities. Bacteroides and Megamonas emerged as dominant contributors. Glycoside hydrolases and carbohydrate esterases were identified as the primary enzymes facilitating their breakdown. These findings suggest that the fine structure of pectin exerts a selective effect on fermenting consortia. Furthermore, both RRTP-1 and RRTP-2 show promise as effective prebiotics.