Characterization and biological activities of cyclic (1 → 3, 1 → 6)-β-glucans from Bradyrhizobium japonicum

Objective: To isolate cyclic (1 → 3, 1 → 6)-β-glucan from Bradyrhizobium japonicum MTCC120, to characterize its structure and to study its biological activities. Results: The degree of polymerization of cyclic (1 → 3, 1 → 6)-β-glucan varied between 10 and 13 and with substituents acetyl, succinyl and phosphocholine. The cyclic glucans showed bimodal particle size distribution, with hydrodynamic diameters of 1.92 and 231 nm corresponding to monomeric and aggregated cyclic glucans, respectively. SEM and TEM images showed that the glucans formed aggregates of nanorods. The glucans were biocompatible, exhibited good antioxidant activity and had the abilities to bind to Aniline Blue dye to form a fluorescence complex which was concentration dependent. Conclusion: The glucans isolated are cyclic and have good antioxidant activities, hence have potential application in food and pharmaceutical industries. Their dye binding ability could be exploited in medical imaging to reduce the cytotoxicity of the dyes.