Rheological characterization of tomato concentrates and the effect on uniformity of processing

Rheological characterization of tomato concentrates was performed using MR flow imaging with a 0.6T 1H spectrometer. The experimental design included four concentrations (6,9,12, and 16 degress Brix) and four temperatures (20, 50, 90, and 110 degrees C). The flow profiles were best characterized by a Herschel-Bulkley expression. Apparent viscosity showed Arrhenius-type behavior with temperature. Yield stress values were determined directly from the plug region of the flow profiles and independent pressure drop measurements. Yield stresses ranged from 1.3 to 51 Pa and were a function of both temperature and concentration. In addition, slip velocities, which ranged from 2.3 to 7.8 cm/s, were obtained directly from velocity profiles. The slip velocities were analyzed by ANOVA; the mean values were significantly different with respect to both temperature and concentration. Based on this study, the RTD of tomato concentrates is narrower with increasing temperature and concentration during thermal processing du...