Journal
FOOD HYDROCOLLOIDS
Volume 20, Issue 5, Pages 730-739Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.foodhyd.2005.07.002
Keywords
locust bean gum; thixotropy; transient rheological behavior; interchain association
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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.
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