A Comparative Study of Physicochemical and Rheological Properties of Iranian Tomato Pastes

In this study, the physicochemical properties and rheological behavior of a number of tomato pastes manufactured by Iranian food processors were compared. Chemical composition tests, color measurement, consistency and rotational viscometry were performed. There were significant differences among the samples in terms of Brix, salt level, vitamin C and Hunter color parameters (L and a/b). Some of the parameters did not pass the standard requirements set by the Institute of Standards and Industrial Research of Iran (ISIRI), e.g. Brix, color and salt. The rotational viscometry tests and shear stress–shear rate curves at 30, 45 and 60°C indicated the existence of variations among the samples in terms of apparent viscosity and yield stress. All tomato paste samples in this study were non-Newtonian fluids and the apparent viscosity of the pastes decreased with temperature increase. The rheological data obtained were fitted using a Power Law equation. The differences were attributed to raw material variations and processing conditions.