Flow Properties of Tomato Concentrates: Effect of Serum Viscosity and Pulp Content

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Abstract
Shear rate‐shear stress data were obtained on tomato serum samples at 5.6, 10, 15, and 20° Brix, and on 28 concentrates prepared from the serum samples and containing different amounts of pulp: +30%, +20%, +10%, normal, −10%, −20%, and −30%. Serum samples were Newtonian fluids while concentrates were shear‐thinning non‐Newtonian fluids. Apparent viscosities of concentrates increased linearly with pulp content expressed as weight %, volume %, or the weight ratio of pulp to serum. Apparent viscosity of the concentrates (η100 conc) was related to the viscosity of serum (η serum) and pulp content (P) by the expression: η100 cone =η serum + A * P ** B. The contribution of pulp content to η100 cone was much more than that of serum. η serum was well correlated with pectin content by the expression: η serum = A1+ B1 (Pectin) ** C1.