Irreversible Shear Thinning and Thickening of Tomato Juice

Tomato juice behaves as a weak gel of pulp network. Shearing of the juice disrupts that pulp network causing an irreversible loss of viscosity, that follows a first order kinetics with a time constant that is shorter the higher the shear rate (e.g. 900, 80 and 15 s for rates of 10, 100 and 1000 s -1 , respectively). However, at a high enough shear rate (e.g., 1000 s -1 ) the disruption of the pulp structure is immediately followed by a counteracting process that partially restores the capability of the suspended particulates to reform a new network and in turn recover a large part of the lost viscosity. Unfortunately, that recovery process requires high enough shear rate and long time, a combination which is rare in common industrial practice. Normally, the mechanical shearing during processing of tomato juice might be a major cause of an irreversible loss of viscosity.