Structural characterization of six new Lepidium meyenii polysaccharides and their effects on gut microbiota in vitro

Lepidium meyenii Walp. (maca) is known for its bioactive polysaccharides but has limited research. In this study, six new polysaccharides including one α-glucan (MCP-3) and five (un)saturated homogalacturonan (MCP-4a, MCP-4b, MCP-4c, MCP-5a, and MCP-5b) were isolated from maca. The structural analysis revealed that the molecular weight of MCP-3 was 1950.99 kDa and its main chain contained both 1,6-α-D-Glcp and 1,3,6-α-D-Glcp units with trace amounts of T-α-D-Glcp as branches linked at the O-3. Five homogalacturonans had a similar structure, composed of GalpAOMe and GalpA with molecular weights ranging from 6.48 kDa to 36.10 kDa. Among them, the structure of MCP-4c was characterized, revealing T-α/β-D-GalpA, T-α-D-Δ^4,5-GalpA, 1,4-α-D-GalpA-(6-OMe), 1,4-α-D-GalpA-(3-OAc), 1,4-α-D-GalpA-(2-OAc), and 1,4-α-D-GalpA residues. Furthermore, the influence of MCP-3, MCP-4 (4a, 4b, 4c), and MCP-5 (5a, 5b) on human gut microbiota was evaluated by the in vitro fermentation experiment. The dynamic changes suggested that these samples were effectively degraded and transformed into short-chain fatty acids during the fermentation process. Additionally, 16S rRNA sequencing revealed that maca polysaccharides significantly increased the relative abundance of probiotics Bacteroidetes, while the growth of harmful Escherichia-Shigella was inhibited. These findings suggest that glucans and homogalacturonans from maca could play a significant role in improving gut health.