PHYSICAL AND STRUCTURAL-PROPERTIES OF BARLEY (1-]3),(1-]4)-BETA-D-GLUCAN .1. DETERMINATION OF MOLECULAR-WEIGHT AND MACROMOLECULAR RADIUS BYLIGHT-SCATTERING

(1-->3),(1-->4)-beta-D-Glucan purified from the 65 degrees C water ext ract of barley flour, commercial beta-glucans and samples obtained by controlled depolymerisation of the former, covering a range from 9 x 1 0(3) to 6 x 10(5) dalton, were characterised by size exclusion chromat ography and light scattering. The on-line measurement of molecular wei ght with a multiangle laser-light scattering photometer gave reproduci ble and consistent values according to: (a:) the process followed in s ample preparation; (b) their chromatographic elution in terms of hydro dynamic volume; and (c) the kinetics of depolymerization. However, bat ch light scattering measurements of beta-glucan molecular weights did not give concordant and reproducible results. These last data, togethe r with the study of the very early stages of enzymatic degradation of high molecular weight beta-glucans by barley endo-beta-glucanases as m onitored by the Cclcofluor-F.I.A. method, seem to suggest the formatio n of very labile molecular aggregates. (C) 1997 Elsevier Science Ltd.