THE ROLE OF PULP INTERPARTICLE INTERACTION IN DETERMINING TOMATO JUICE VISCOSITY

Pulp interparticle interaction plays a major role in determining the viscosity of tomato juice. Indices of second order and of compounded high order interparticle interaction have been evaluated by diluting tomato juice samples with their own serum, and determining the slope of the reduced viscosity curves at the very dilute and at the original concentration regions, respectively. The second order interaction index, reflecting the behavior of a pair of colliding particles, has practically a similar value for samples having the same process history. On the other hand, tomato juice samples differ markedly in their value of the interaction index describing the effect of high order interparticle interaction on the viscosity at the original juice concentration. The higher that value, the higher the viscosity. The value of this index decreases by concentrating the tomato juice and increases by homogenization. It has a maximum value at pH 4-4.5 and most importantly it is greatly dependent on the mechanical abuse history of the juice. Enzymatic depolymerization of the soluble and especially the insoluble pectin markedly reduces the value of the interaction index, indicating that pectin plays a major role in determining the level of that interparticle interaction.