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 η0/η∞, 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.