Structural characterization and in vitro analysis of the prebiotic activity of oligosaccharides from lotus (Nelumbo nucifera Gaertn.) seeds

In the present study, lotus seed oligosaccharides (LOSs) were isolated from lotus ( Nelumbo nucifera Gaertn.) seeds using preparative liquid chromatography. LOS structures were characterized using fourier transform infrared spectroscopy (FT-IR), acid hydrolysis, tandem   mass spectrometry (MS/MS) and 1D/2D nuclear magnetic resonance (NMR) spectroscopy. Then, Lactobacillus acidophilus was used to evaluate the prebiotic activity of LOSs in vitro. The structural analysis revealed that the monosaccharide components of LOSs included glucose, mannose, fructose and galactose. The MS/MS results indicated that disaccharides, trisaccharides, trisaccharides and tetrasaccharides were the constituents of isolated oligosaccharide polymers LOS2, LOS3-1, LOS3-2, and LOS4, respectively. The FT-IR and 1D/2D NMR data confirmed that LOS3 and LOS4 had a linear structure consisting of (1 → 6)- α - d -mannopyranosyl and glucopyranosyl residues. LOS3-1 and LOS4 effectively and selectively promoted the growth of an L. acidophilus strain, according to the results of the assays of optical density and the short-chain fatty acid (SCFA) content in the culture broth.