Abstract
Beta 1–3, 1–4 glucans (“beta-glucans”) are one of the key components of the cell wall of cereals, complementing the main structural component cellulose. Beta-glucans are also an important source of soluble fibre in foods containing oats with claims of other beneficial nutritional properties such as plasma cholesterol lowering in humans. Key to the function of beta-glucans is their molecular weight and because of their high polydispersity - molecular weight distribution. Analytical ultracentrifugation provides a matrix-free approach (not requiring separation columns or media) to polymer molecular weight distribution determination. The sedimentation coefficient distribution is converted to a molecular weight distribution via a power law relation using an established procedure known as the Extended Fujita approach. We establish and apply the power law relation and Extended Fujita method for the first time to a series of native and processed oat beta-glucans. The application of this approach to beta-glucans from other sources is considered.
Highlights
Beta 1–3, 1–4 glucans, “beta-glucans”, are one of the key polysaccharides of the cell walls of oats and other cereals, complementing the main structural component cellulose[1,2,3]
S = κsMwb where s is the sedimentation coefficient, Mw is the weight average molecular weight and κs and b are characteristic coefficients related to conformation
The sedimentation coefficient s depends on the size and shape of the macromolecule[12] but if κs and b are known Mw can be found from: Mw = (s/κs)1/b
Summary
The inherent fractionation ability of the sedimentation velocity method without the need for columns or membranes, together with the automatic removal of supramolecular impurities appears to be useful for impure or incompletely soluble materials. The Calcofluor fluorescence-labelled chromatography method7,29 – specific for β(1–4) bonds - has proved useful for the analysis of the molecular weight of beta-glucans in the presence of non β(1–4) containing impurities, for distributions containing substantial amounts of high molar mass material >500,000 g/mol the Calcofluor method results in an increasing underestimation of the molecular weight[7,29]. For such systems the Extended Fujita method provides a useful complementary approach. We are exploring the extension of our approach to other beta-glucans, most notably from barley and wheat
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