Texture flow property

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. 

The big difference between normal isotropic liquids and nematic liquids is the effect of anisotropy on the viscous and elastic properties of the material. Liquid crystals of low molecular weight can be Newtonian anisotropic fluids, whereas liquid crystalline polymers can be rate and strain dependent anisotropic non-Newtonian fluids. The anisotropy gives rise to 5 viscosities and 3 elastic constants. In addition, the effective flow properties are determined by the flow dependent and history dependent texture. This all makes the rheology of LCPs extremely complicated. 

Rao, M. A. 1977b. Measurement of flow properties of fluid foods—developments limitations, and interpretation of phenomena, y. Texture Stud. 8 257-282. 

Benezech, T. and Maingonnat, J. F. 1993. Flow properties of stirred yoghurt structured parameter approach in describing time dependency. J. Texture Sud. 24 455-473. 

Figoni, P. I. and Shoemaker, C. F. 1983. Characterization of time dependent flow properties of mayonnaise under steady shear.. 7 Texture Stud. 14 431-442. 

Dannenberg, F., and Kessler, H.G. (1988b). Effect of denaturation of p-lactoglobulin on texture properties of set-style nonfat yoghurt. II. Firmness and flow properties. Milchwissenschaft 43, 700-704. 

Following Scott Blair s (11) classification of instruments for the study of texture, the instruments for measuring the flow properties of fluid foods can be classified into the categories (1) fundamental, (2) empirical, and (3) imitative. Fundamental tests measure well defined properties utilizing geometries that are amenable to analysis of fluid flow. Empirical tests measure parameters that are not clearly defined, but the parameters have been shown to be useful from past experience. Imitative tests measure properties under test conditions similar to those in practice (11) ... 

Many products in the chemical and agrochemical, cosmetic, pharmaceutical, and food industries are emulsion-based. Their internal structure is composed of one or more fluids, with one being flnely dispersed as droplets within the other one. The size distribution of the droplets mainly influences characteristic product properties as color, texture, flow- and spreadability, viscosity, mouth-feel, shelf-life stability, and release of active ingredients. It therefore has to be maintained for the life-time of a product. Due to the extremely high interfacial area in these systems, this microstructure is thermodynamically unstable. By applying emulsiflers and thickeners, emulsions are kinetically stabilized for a certain amount of time. Elowever, shelf-life stability always is a big chal-... 

Although polymers and wormlike micelles are very different in nature, the flow properties of their nematic phases are similar. This property was ascribed to the existence of textures at a mesoscopic scale, and to the fact that the dynamics of the textures dominate the mechanical responses of these fluids [310]. 

Where the support surface is three-dimensional (3D), fibres can be displaced from the projections in the surface to produce local density variations or texture in the fabric that can influence tensile and fluid flow properties, as well as introducing variations in local fibre segment orientation. 

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