Viscometric Behavior of Reconstituted Tomato Concentrate

Abstract

The rheological properties of tomato concen- trates produced by hot and cold break have been exten- sively studied by many authors. Only a few studies, however, focus specifically with the rheology of reconsti- tuted concentrates from tomato powders. In this study, the rheological properties of reconstituted tomato concentrate from lyophilized freeze-dried tomato juice were evaluated using rotational viscometer at temperatures 20°C, 30°C, 40°C, 50°C, and 60°C and at concentrations of 9.7%, 12.9%, 20.5%, and 26.8% total soluble solids. Using power law model, both flow behavior index (n) and consistency coefficient (k) were determined. The calculated values of flow behavior index (n) were less than unity (0.03-0.28) at all temperatures and concentrations indicating the shear- thinning characteristic of the concentrate. The effect of temperature and concentration on the consistency coeffi- cient (k) was studied. Positive correlation between k in the range of 1.57 and 38.33 Pa s n and inverse absolute temperature (1/T) has been shown by Arrhenius model. Additionally, linear correlation between consistency coeffi- cient (k) and concentration (C )w as determined. The activation energies were found in the range of 3.63 and 7.36 kJ/mol K depending on concentration. The results of this study might be useful to improve the design of processing operations dealing with tomato powder reconstitution.