Preparation of individual galactan oligomers, their prebiotic effects, and use in estimating galactan chain length in pectin-derived polysaccharides

Galactans exhibit many biological activities, including modulation of human gut microbiota. By optimizing hydrolysis conditions and fractionation protocols, we purified a series of galacto-oligosaccharides from potato galactan, with degrees of polymerization (DP) up to 15. These oligosaccharides were characterized by using HPAEC, MALDI-TOF, ¹H¹³C-NMR HSQC and HMBC experiments. Analysis of NMR data allowed chemical shift assignments to be made for oligos up to DP15. We used these NMR data to calculate intensity ratios of resonances from non-terminal to terminal residues, and correlated them with galactan chain length. Using this approach, we were able to estimate the length of galactan side chains in complex rhamnogalacturonan-I polysaccharides. Furthermore, we demonstrate here that prebiotic effects on Lactobacillus bacteria are related to galactan chain length, suggesting a potential application in the study of the human gut microbiome.