Aggregation and gelation of oat β-glucan in aqueous solution probed by NMR relaxometry

Nuclear magnetic resonance was used to study water proton transverse relaxation in oat β-glucan aqueous solutions during storage. The molecular weights of the samples ranged from 112 to 494kDa. The polysaccharide structure was identified by IR, GC-MS, NMR spectroscopy, and high performance anion exchange chromatography. In 1% solutions, 494kDa β-glucan formed stable solution phase. Aggregates were generated in the solution of low molecular weight polysaccharide. The transverse relaxation time of water associated with the aggregate microphase was about 15ms. The majority of the solution was bulk water, with a relaxation time of 800-1600ms. The proton exchange rate was about 10³s^-1, calculated from two-site exchange model. The proportion of β-glucan in the aggregate microphase increased from 0 to over 80% of the total β-glucan during storage of 112kDa samples. In the 4% solutions, the evolution of water proton relaxation associated with the gel network can be explained by the fractal structure theory. The relaxation behavior suggested the growth and syneresis of the gel network during the gelation of the low molecular weight β-glucan solutions.