Interchain association of locust bean gum in sucrose solutions: An interpretation based on thixotropic behavior

The thixotropic behavior of locust bean gum (LBG) in sucrose solutions after freezing and thawing was investigated using a transient rheological approach. The thixotropy is attributed to the forced association of LBG chains during freezing. The effects of shear rate, shearing temperature, sucrose concentration, and number of freeze-thaw cycles on the transient viscosity profile were studied. A second-order kinetic equation for structure breakdown is found to describe well the transient viscosity profile, showing a rate constant of an order of 0.1 s(-1) in terms of the dimensionless structure parameter for the 2.5% LBG 30% sucrose solution. The rate constant strongly depends on the shear rate, shearing temperature, and number of freeze-thaw cycles, the last dependence indicating its relation to the pore size of LBG network. The ratio of the initial to equilibrium viscosity eta(0)/eta(infinity), reflecting the amount of associations ruptured under shear, appears almost constant throughout the measurement. It is speculated that only part of the associations can be probed at a constant shear rate. For the LBG solutions with sucrose content below 15% or subjected to successive freeze-thaw cycles, transient viscosity profiles cannot be obtained due to elasticity caused by the formation of an infinite polymer network. (c) 2005 Elsevier Ltd. All rights reserved.