Rheological studies of barley (1→3)(1→4)-β-glucan in concentrated solution:: mechanistic and kinetic investigation of the gel formation

The gelation of concentrated barley (1-->3)(1-->4)-beta-glucan solutions was investigated. The gelation rate was quantified by a novel parameter called the elasticity increment I-E, accessible via oscillatory time experiments. Decreasing molar mass and increasing concentration proved to raise the gelation rate. Despite a very similar plateau storage modulus G'(p) of the final gels for a given concentration, the mechanical stability increases with increasing molar mass. Oat beta-glucan and lichenan, both (1-->3)(1-->4)-beta-glucans, are also able to form solid gels. The turbidity, syneresis, melting temperature of the gels and the gelation rate increase in the order oat beta-glucan, barley beta-glucan and lichenan, indicating an increasing extent of the junction zones. Examination of the fine structure revealed the most regular chain structure for lichenan, with cellotriose units linked by beta-(1-3) bonds as the main structural feature. From this it was deduced that sections of consecutive cellotriose units constitute the cross-links. A gelation model based on sporadic nucleation similar to crystallization of polymer melts is proposed. (C) 1999 Elsevier Science Ltd. All rights reserved.