Rheological studies of barley (1→3)(1→4)-β-glucan in concentrated solution:: investigation of the viscoelastic flow behaviour in the sol-state

A (1 --> 3)(1 --> 4)-beta-D-glucan isolated from barley by a set of commercial beta-glucans differing in molecular size was characterized by means of viscometry and size exclusion chromatography coupled with multi-angle laser light scattering. A eta(0)-M-w-c relationship (eta(0) = 10(-3) + 6.04 x 10(-5) cM(w)(0.71) + 2.56 x 10(-6)c(2)M(w)(1.42) + 2.70 x 10(-15)c(5.18)M(w)(3.68)) did not reveal any evidence of association tendencies in the concentrated fresh solution either. However, rheological measurements showed a transition from typical viscoelastic behaviour to gel-like properties over a period of several hours, with a long induction period which allows rheological measurements in the sol state. In shear experiments the concentrated beta-glucan solutions showed flow irregularities correlating with a Weissenberg number (N-1/tau) in the range 1-3. Repeated cycles of short-term steady shear and rest periods accelerated the sol-gel transition, whereas steady shear did not induce gelation. Barley beta-glucan in freshly prepared aqueous solution behaves like a viscoelastic liquid, without any associated structures being detected even over a period of several hours, despite its ability to form solid gels. (C) 1999 Elsevier Science Ltd. All rights reserved.