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)-β-d-glucan isolated from barley by a set of commercial β-glucans differing in molecular size was characterized by means of viscometry and size exclusion chromatography coupled with multi-angle laser light scattering. A η0–Mw–c relationship (η0=10−3+6.04×10−5cMw0.71+2.56×10−6c2Mw1.42+2.70×10−15c5.18Mw3.68) 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 β-glucan solutions showed flow irregularities correlating with a Weissenberg number (N1/τ) 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 β-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.