Effect of concentration of porang flour and temperature on rheological properties of tomato ketchup

Abstract

The rheological properties of fluid and semisolid foodstuffs is important in the design of flow processes in the quality control, storage stability, and in understanding and designing texture of the product. The viscosity of tomato ketchup is one of the major quality components for consumer acceptance. The tomato ketchup is a semisolid material, which obtain its viscosity from naturally occurring pectic substances in fruits. Enzymatic degradation, pectic/protein interaction, pulp content, and homogenization process may affect the consistency of tomato product. These inconsistencies may be diminished by the addition of hydrocolloids. In this study, the flow properties of tomato ketchup were evaluated upon addition of different concentrations of porang flour (0.25%, 0.50% and 0.75%) and in various temperatures (25, 35, 45 and 55 °C). The flow behaviour was characterized by fitting the experimental data of each formulations to the power-law and Herschel-Bulkley model. The Arrhenius equation was used to describe the effects of temperature on the apparent viscosity of the tomato ketchup formulations. The temperature dependency was assessed to evaluate the stabilizing effect of different concentrations of porang flour on tomato ketchup. Increasing porang flour concentration in tomato ketchup resulted in a decline of the activation energy.