Texture rheological parameters

Texture is a key component of the quality and palatability of potato products. Texture is generally quantified by measuring the resistance of a product to an applied force. A number of different rheological parameters can be used to evaluate a range of tuber characteristics such as firmness, hardness, softness, adhesiveness, fracturability, etc. There is a considerable amount... 

Solomon, W. K., Jindal, V. K. (2003b). Modeling thermal softening kinetics of potatoes using fractional conversion of rheological parameters. J. Texture Stud., 34, 231-247. 

In contrast to the mechanical and rheological properties of materials, which have defined physical meanings, no such definitions exist for the psychophysical assessment of equivalent textural properties of foods. To identify material properties, or combinations of these, which are able to model sensory assessments requires a mixture of theory and experimentation. Scientific studies of food texture began during the twentieth century by the analysis of the rheological properties of liquid or semi-solid foods. In particular Kokini14 combined theoretical and experimental approaches in order to identify appropriate rheological parameters from which to derive mathematical models for textural attributes of liquid and semi-solid foods, namely, thickness, smoothness and creaminess. 

These rheological parameters have been successfully correlated to textural attributes of hardness and spreadabUity and provide information pertaining to the fat crystal network (69). The value of G is useful in assessing the solid-like stmcture of the fat crystal network. Increases in the value of G typically correspond to a stronger network and a harder fat (66). Alternatively, G" represents the fluid-like behavior of the fat system. This value can be related to the spreadability of a fat system, because increases in G" indicate more fluid-like behavior under an applied shear stress. The tan 8 is the ratio of these two values. As the value of 5 approaches 0° (stress wave in phase with stress wave), the G" value approaches zero, and therefore, the sample behaves like an ideal solid and is referred to as perfectly elastic (68). As 8 approaches 90° (stress is completely out of phase relative to the strain). 

There seems to be a correlation between the sensorial texture parameter ( thickness as measured by the spoon test) and the rheological parameters G (the storage modulus, the elastic component) and G" (the loss modulus, the viscous component). One of the most useful parameters to measure is tan S,... 

Jones, D. S., Lawlor, M. S., and Woolfson, A. D. (2002), Examination of the flow rheological and textural properties of polymer gels composed of poly(methylvinylether-co-maleic anhydride) and poly(vinylpyrrolidone) Rheological and mathematical interpretation of textural parameters,/. Pharm. Sci., 91,2090-2101. 

Textural characteristics of butter significantly depend on milkfat composition and the method of manufacture. If the chemical composition of the milkfat is known, it is possible to select the appropriate technological parameters of the buttermaking to improve its texture. To obtain butter with constant rheological characteristics and to control the parameters of the buttermaking process, it is necessary to take into account the difference in the chemical composition and the properties of the milkfat in various seasons. Table 13 shows various compositional changes of milkfat derived from summer and winter mUk (36). 

In the present chapter the effect of sucrose and hydrocolloids (xanthan gum, guar gum, and sodium alginate) on (i) Tg of the freezeconcentrated matrix (7 ), (ii) amylose and amylopectin retrogradation, and (iii) rheological behavior of the system, are analyzed in gelatinized water-starch formulations frozen at different rates and stored at — 18°C. Besides, the importance of Tg as a parameter related to texture quality of starch-sucrose-hydrocolloids-based foods during frozen storage is discussed. 

Two important parameters that describe a foam are texture and stability. Although both are dominant factors in the determination of foam rheology, neither is stipulated but is assumed when designing a foam fluid treatment. 

Texture. Foam texture is an important parameter that affects the rheology of the foam fluid. Texture of a foam is a means of classifying a foam according to its bubble size, shape, and distribution within the foam matrix. Texture is a description of the manner in which the gas bubbles are distributed throughout the liquid phase of the foam. This property not only influences the foam s rheology but also its fluid loss, proppant transport, and cleanup properties. The texture of a foam is a qualitative rather than a quantitative value, and therefore a number cannot be used to describe it a physical description will be used. Factors that effect the texture of foams are quality, pressure, foam generating technique, and chemical composition. 

Doi [23] had already noted that his theory was restricted to a monodomain or textureless sample. The extension by Marucci and Maffettone [68] retains that restriction. This issue was addressed by Larson and Doi [72], who proposed a model for the rheology of textured lyotropic solutions in the tumbling regime. In the linear Larson-Doi polydomain model the response of the material is expressed in terms of a variable / proportional to the defect density. The defect density is proportional to the shear rate, so that texture refinement is a feature of this model. The steady state predictions for the order parameter S are independent of shear rate. 

Most forming processes involve the use of suspensions, sols or gels (pastes). In order to solve hcindling problems or to tailor the rheological properties of these media to suit a particular forming process, one can act on mechanical parameters (choice and operation of equipments), modify the surface chemistry of the suspended or gcJled particles ( ect of pH, additives) or use a binder (colloidal silica, alumina,...). Such actions generally affect the final properties that the catalyst has to meet (textural, mechanical and catalytic requirements). 

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