Viscosity, tomato juice

PE + - High viscosity tomato juices and pastes (hot PG break)... 

The observed increase in serum and efflux viscosity of juice from transgenic tomato fruits was most likely due to changes in pectin chemistry as a result of reduced levels of PME activity. Since viscosity is affected by the volume occupied by the molecule or the extent of molecular association in solution, both molecular weight and DOM will enhance the viscosity of the juice [26]. Since juice from... 

Takada and Nelson [25] reported a correlation between PPT value and Bostwick and efflux viscosity of tomato products. Thakur et al. [22] also showed a correlation between Bostwick and efflux viscosity and PPT value. They also reported a linear relationship between PPT value and serum viscosity (r =0.979), described by the equation, Y = 33 X-255 (X, PPT value Y, serum viscosity). As juice from transgenic fruits contained higher PPT value, its higher viscosity values are in line with the reported literature. 

Kalamaki, M.S., Harpster, M.H., Palys, J.M., Labavitch, J.M., Reid, D.S., Brummell, DA. (2003). Transgenic overexpression of expansin influences particle size distribution and improves viscosity of tomato juice and paste. J. Agric. FoodChem. 51, 7456-7464. 

However, they may not indicate the true bulk viscosity of a suspension that forms a thin layer of the continuous phase (e.g., serum of tomato juice) around the immersed probe or when the probe is covered by a higher viscosity gel due to fouling. Vibrational viscometers are suitable for measuring viscosities of Newtonian fluids, but not the shear-dependent rheological behavior of a non-Newtonian fluid (e.g., to calculate values of the power law parameters). 

Measurement and analysis. The viscosity of tomato juice was measured using Tokyokelkl BH type disc rotating viscosimeter. 

Water flux. Secondly, the effects of factors which were anticipated to influence the membrane performance and the system efficiency were evaluated. They were the osmotic pressure and the viscosity of tomato juice as the function of juice concentration and feed velocity, and operating pressure. It was observed that the rise in temperature increases water flux. 

Figure 6 represents the relationship between tomato juice viscosity and flow velocity. The measurement was done with the juice prepared from canned paste, using a disc rotating viscosimeter. The value, viscosity multiplied by velocity was nearly Independent of the velocity. This suggests that the effect of flow velocity on the pressure drop would be small. This allows the variation of juice feed velocity in a wide range without significant change in pressure drop. 

In Figure 7, the viscosity of tomato juice Increases nearly exponentially with juice concentration. As anticipated from the results shown in Figure 7, pressure drop rises almost exponentially with increase in concentration when fresh tomato juice was fed in a thin tube of 0.4 cm inner diameter (Figure 8). 

Figure 7. The effect of tomato juice concentration on the viscosity observed at 20°C by using a disc-rotating viscosimeter...

Tanglertpaibul and Rao (AS) found that in the range of finisher screen openings (FSO) 0.508 to 1.143 mm, smaller FSO yielded lower apparent viscosities evaluated at a shear rate of 100 sec-1 (T ioo) However, concentrates from 0.686 mm screen had the highest apparent viscosity. Similar results were found for tomato juice also. This phenomena can be explained in that small screens reduced the size of solid particles and at the same time remove some of the large particles. The net result is that one obtains finished products with narrow particle size distribution and a small amount of large particles. 

Heat alters the structure of pectic substances by means of hydrolysis. Colloidal properties of serum may be altered by heat resulting in lower apparent viscosity of reconstituted tomato concentrates with unheated pulp. Caradec and Nelson (53.) also reported that viscosity of tomato juice serum decreased with heat treatment. 

The rheological properties of fluid tomato sauce products are important quality parameters. The flow properties of the juice, i.e viscosity and consistency, are determined primarily by the insoluble components [180-186]. The viscosity of the serum, the soluble fraction of the tomato juice after removal of insoluble material, is mainly determined by the polymeric substances, mostly pectin, i.e., the flow... 

Inosine monophosphate (IMP, disodium salt) and 5 -guanosine monophosphate (GMP, disodium salt) have properties similar to MSG but heightened by a factor of 10-20. Their flavor enhancing ability at 75-500 ppm is good in all food (e. g. soups, sauces, canned meat or tomato juice). However, some other specific effects, besides the MSG effect , have been described for nucleotides. For example, they imprint a sensation of higher viscosity in liquid food. The sensation is often expressed as freshness or naturalness , the expressions body and mouthfeel being more appropriate for soups. 

Chapter HI relates to measurement of flow properties of foods that are primarily fluid in nature, unithi.i surveys the nature of viscosity and its relationship to foods. An overview of the various flow behaviors found in different fluid foods is presented. The concept of non-Newtonian foods is developed, along with methods for measurement of the complete flow curve. The quantitative or fundamental measurement of apparent shear viscosity of fluid foods with rotational viscometers or rheometers is described, unithi.2 describes two protocols for the measurement of non-Newtonian fluids. The first is for time-independent fluids, and the second is for time-dependent fluids. Both protocols use rotational rheometers, unit hi.3 describes a protocol for simple Newtonian fluids, which include aqueous solutions or oils. As rotational rheometers are new and expensive, many evaluations of fluid foods have been made with empirical methods. Such methods yield data that are not fundamental but are useful in comparing variations in consistency or texture of a food product, unit hi.4 describes a popular empirical method, the Bostwick Consistometer, which has been used to measure the consistency of tomato paste. It is a well-known method in the food industry and has also been used to evaluate other fruit pastes and juices as well. 

F re 5-13 Log-log Plot of the Apparent Viscosity at 100 s versus Total Solids of Tomato Concentrates from 475 and New Yorker Tomatoes Using Hot-Break Juice the Slopes of the Lines were 2.4 and 2.5, Respectively. 

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. 

When tomato concentrates are diluted to lower concentration, the diluted products have lower viscosity than if they are concentrated straight from the juice. 

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