Elimination of aggregates of (1→3) (1→4)-β-D-glucan in dilute solutions for light scattering and size exclusion chromatography study

Abstract

Methods for eliminating aggregates of cereal (1→3) (1→4)-β-D-glucan in dilute solutions were investigated using dynamic light scattering and size exclusion chromatography. Wheat β-D-glucan samples were selected and dissolved in various solvents under different preparation conditions. The molecular size distribution was monitored by dynamic light scattering measurement. In most of the solutions, there were two well separated species of different average sizes. It appeared that the specie with smaller average size represented the un-aggregated molecules (unimers) and the specie with larger particle size corresponded to the aggregates. The results showed that heat treatment, filtration, ultrasonication, and the use of urea solution (up to 6 M) could not eliminate aggregates completely. However, the percentage of aggregates in aqueous NaOH solution decreased significantly with the increase of NaOH concentration. In 0.5 M NaOH solution, no aggregation was detectable by dynamic light scattering measurement. Both dynamic light scattering and HPSEC data showed that wheat β-D-glucan was stable in 0.5 M NaOH solution without any noticeable degradation when stored at 25 °C for 12 h. The results of present study suggested that 0.5 M NaOH solution is a suitable solvent for cereal β-D-glucans. Using this solvent, the molecular characteristics of wheat β-D-glucan was studied by both dynamic and static light scattering. The weight average molecular weight ( M w), radius of gyration ( R g), hydrodynamic radius ( R h), and the second virial coefficient ( A 2) were obtained with the values of 3.29×10 5 g/mol, 45.6 nm, 26.2 nm, and 1.04×10 −3 cm 3 mol/g 2 respectively. This study also confirmed that wheat β-glucan in solution exhibited a random coil conformation.