Visualization of Single and Aggregated Hulless Oat (<i>Avena nuda</i> L.) (1→3),(1→4)-β-d-Glucan Molecules by Atomic Force Microscopy and Confocal Scanning Laser Microscopy

Surfactants were used to disperse oat β-glucan. Atomic force microscopy (AFM) images of the resulting samples revealed a distribution of extended chainlike molecules and allowed, for the first time, direct visualization of single oat β-glucan molecules with cross-sectional heights of about 0.44 nm. The number-average contour length (<i>L</i><sub>n</sub>) and root-mean-square end-to-end distance (〈<i>R</i><sub>ee</sub><sup>2</sup>〉<sup>1/2</sup>) measured from the AFM images were 938 and 912 nm, respectively. The calculated persistence length (<i>L</i><sub>p</sub>) was 526 nm. The weight-average molecular weight (<i>M</i><sub>w</sub>) calculated from single β-glucan molecules was 4.43 × 10<sup>5</sup>. Samples without surfactant showed a strong tendency to form aggregates. The sample concentration, reserving time, and calcofluor as well as freezing could affect the formation of aggregates. These aggregates were visualized by both AFM and confocal scanning laser microscopy. The shape of the aggregates changed from small dots with diameters of approximately 20−50 nm to microfibrils over 3 μm long with the increasing of the concentration of oat β-glucan from 10 to 100 μg/mL. The particle size distribution obtained by a laser particle size analyzer was 926 nm, which confirmed the size of oat β-glucan molecules obtained from AFM images. Keywords: Oat; β-glucan; atomic force microscope; confocal scanning laser microscopy; sodium dodecyl sulfate; particle size