Tomato concentrates, rheological properties

Because of the compressible nature of food dispersions, the direct determination of the magnitude of centrifugal force employed in the separation of the phases. Therefore, rheological properties of plant food dispersions, such tomato concentrates and concentrated orange juice, are based on the mass of pulp. In starch dispersions, they are based on the mass fraction of starch granules, denoted as cQ, as described in Chapter 4. 

Somsrivichai, T. 1986. A study on rheological properties of tomato concentrates as affected by concentration methods, processing conditions, and pulp content, Ph.D. thesis, Cornell University, Ithaca, NY. 

Tanglertpaibul, T. and Rao, M. A. 1987a. Rheological properties of tomato concentrates as affected by particle size and methods of concentration. J. Food Sci. 52 141-145. 

The effect of different flow properties on heat transfer to canned dispersions undergoing intermittent axial rotation was studied by Tattiyakul et al. (2002b). In addition to the 3.5% cornstarch dispersion discussed above, a 5% CWM dispersion whose rheological data are shown in Figure 8-9 and a tomato concentrate that followed a simpler thermo-rheological behavior were studied. Because of the high apparent viscosity over a wide temperature range of the CWM dispersion, it had the slowest time-temperature profile (not shown here). Results on the effect of continuous axial rotation on heat transfer to a canned starch dispersion can be found in Tattiyakul (2001). 

Plant food dispersions such as tomato concentrates and concentrated orange juice are important items of commerce. The viscosity function and the yield stress are two important rheological properties that have received considerable attention. Corrections for slip, due to the formation of a thin layer of fluid next to solid surfaces, in a concentric cylinder viscometer depended on the magnitudes of applied torque and on the shear-thinning characteristics of the dispersion. Mixer viscometers were used for obtaining shear rate-shear stress and yield stress data, but the latter were higher in magnitude than those obtained by extrapolation of flow data. 

Finisher screen openings and concentration methods, were found to affect the rheological properties of tomato concentrates. The apparent viscosity of 65 °Brix concentrated orange juice was strongly influenced by temperature. The dispersed phase plays a major role in the magnitude of apparent viscosity and yield stress, and functional relationships for predicting the properties were developed. 

Thus far, recent developments in the measurement of rheological properties were discussed. Next, we consider the rheological properties of important PFDs, such as, tomato concentrates and concentrated orange juice. 

In addition to tomato concentrates and COJ, significant studies have been conducted on the factors affecting the rheological properties of apple sauce and apricot puree. Rao et al. ( 1) found that the consistency index (K) of... 

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