Structural analyses and immunomodulatory properties of fructo-oligosaccharides from onion (Allium cepa)

• Published in: Carbohydrate polymers 2015-03, Vol.117, p.115-122
• Main Authors: Kumar, V. Prasanna, Prashanth, K.V. Harish, Venkatesh, Y.P.
• Format: Article
• Language: English
• Subjects: Allium cepa; Animals; Cell Proliferation - drug effects; Ethanol - chemistry; Free Radicals - metabolism; Fructans - chemistry; Fructans - isolation & purification; Fructans - pharmacology; Fructo-oligosaccharides; Immunologic Factors - chemistry; Immunologic Factors - isolation & purification; Immunologic Factors - pharmacology; Immunomodulation; Intracellular Space - drug effects; Intracellular Space - metabolism; Inulin; Lymphocytes - drug effects; Lymphocytes - immunology; Macrophages, Peritoneal - drug effects; Macrophages, Peritoneal - metabolism; Male; Mice; Mitogenicity; Nitric Oxide - metabolism; Oligosaccharides - chemistry; Onion; Onions - chemistry; Phagocytosis; Phagocytosis - drug effects; Rats; Spleen - cytology
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/j.carbpol.2014.09.039

•Fructo-oligosaccharides (FOS) isolated from hot 80% ethanol extract of onion bulbs.•FOS (3–6 saccharide units analyzed by NMR and ESI–MS) used as a pool in this study.•Onion FOS (1.7% yield) are inulin-type fructans with β-d-Glc at the non-reducing end.•They display significant mitogenic activity towards murine thymocytes/splenocytes.•Onion FOS enhance innate immunity by activating murine peritoneal macrophages. Onion (Allium cepa) is an immune-boosting food rich in fructans. The major aim of this study is to characterize and investigate the immunomodulatory properties of onion fructo-oligosaccharides (FOS). FOS was isolated from onion bulbs by hot 80% ethanol extraction (yield: ∼4.5g/100g fw) followed by gel permeation chromatography. NMR of onion FOS revealed unusual β-d-Glc terminal residue at the non-reducing end. TLC and ESI–MS analyses showed that onion FOS ranged from trisaccharides to hexasaccharides. Onion FOS (50μg/mL) significantly increased (∼3-fold) the proliferation of mouse splenocytes/thymocytes vs. control. Further, onion FOS enhanced (∼2.5-fold) the production of nitric oxide by peritoneal exudates cells (PECs) from Wistar rats; intracellular free radicals production and phagocytic activity of isolated murine PECs were also augmented. Our structural and in vitro results indicate that onion FOS comprising of tri- to hexasaccharide units belongs to inulin-type fructans, and possess immunostimulatory activities towards murine lymphocytes and macrophages.