Texture rheological properties

Much progress has been made in recent years in understanding the texture, rheological properties, and microstructures of food colloids using new and ad-... 

The aim of every technologist working with food dispersions or food colloids is to be able to select the proper amphiphile for a desired application or, even better, to be able, to design a good blend of emulsifiers and/or stabilizers to achieve the desired stability, texture, rheological properties, and other important characteristics. The aim of the scientists is to provide a good understanding of surfactant activities and capabilities and to be able to predict chemical structure and correlate with surface reactivity. 

Eliasson, A. C, Kim, H. R. (1992). Changes in rheological properties of hydroxypropyl potato starch pastes during freeze-thaw treatments I. A rheological approach for evaluation of freeze-thaw stability. J. Texture Stud, 23, 279-295. 

Kaur, L., Singh, N., Sodhi, N. S., Gujral, H. S. (2002). Some properties of potatoes and their starches I. Cooking, textural and rheological properties of potatoes. Food Chem., 79, 177-181. 

Leung, H. K., Barron, F. M., Davis, D. C. (1983). Textural and rheological properties of cooked potatoes. J. Food... 

The term food colloids can be applied to all edible multi-phase systems such as foams, gels, dispersions and emulsions. Therefore, most manufactured foodstuffs can be classified as food colloids, and some natural ones also (notably milk). One of the key features of such systems is that they require the addition of a combination of surface-active molecules and thickeners for control of their texture and shelf-life. To achieve the requirements of consumers and food technologists, various combinations of proteins and polysaccharides are routinely used. The structures formed by these biopolymers in the bulk aqueous phase and at the surface of droplets and bubbles determine the long-term stability and rheological properties of food colloids. These structures are determined by the nature of the various kinds of biopolymer-biopolymer interactions, as well as by the interactions of the biopolymers with other food ingredients such as low-molecular-weight surfactants (emulsifiers). 

An Instron Testing System (Model 1122), fitted with a 10 cm six-wire grid (Ottawa Texture measuring system, OTMS cell) was used to determine rheological properties. A loading rate of 50 mm/min and a chart speed of 500 mm/min resulted in a well defined force-deformation curve. Force at the bioyield point and the area under the curve were calculated. These values were then converted into maximum stress, work and specific work values ... 

TABLE I. Selected Physical and Rheological Properties of Extrusion Texturized Soy... 

Figure 21. Rheological properties of nonextrusion textured (A) soy flour, (B) 25.5% succinylated soy flour, (C) 61.7% succinylated soy flour, and (D) 83% succinylated soy flour. The bars, indicating standard error, that do not overlap indicate a significant difference between the respective means atP 0.05.

Rheology is the science of deformation and flow of matter. In food rheology, the matter of interest is food, and the importance of its deformation and flow relate to several important properties. Of these, texture is the most important. Texture is one of four quality factors of foods the others are flavor, appearance, and nutrition. In the food industry, there are other properties and processes in which rheology has an important role. They include formulation, manufacturing, transportation, and shelf stability. The measurement of the rheological properties of foods provides the food scientist and engineer with critical information necessary for the successful development and delivery of formulated foods to the consumer. 

As yield stress is a very important rheological property of many foods, the slip phenomenon has many important textural and practical processing implications for food products. 

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. 

Clearly, it may be possible to define and accurately measure many aspects of the mechanical and rheological properties of foods, but to try and relate these measures to consumer perceptions of the texture of the foods, is fraught with difficulties. Conversely, it is possible to train human subjects to assess textural characteristics of foods in defined and consistent ways (training them to mimic an instrumental response), however this may be missing the diversity of perceptions of food texture experienced by normal consumers. 

Marshall, R.J. (1989). Composition, structure, rheological properties and sensory texture of processed cheese analogues. J. Sci. Food Agric. 50, 237-252. 

Since sensory and mechanical properties of a food depend on its microstructure, the knowledge of microstructure must precede any operation aimed to the attainment of a specific texture (Ding and Gunasekaran, 1998). The instrumental measurements of mechanical and rheological properties represent the food responses to the forces acting on the food structure and, for this reason, are affected by the way in which these analyses are performed. Furthermore, mechanical and rheological tests are always destructive and make impossible the execution of other analyses. 

Food products must have appropriate texture properties. For example, it is important that mayonnaise products have thick and creamy textures, but not too high a viscosity. The rheological properties depend on their composition, such as the concentration of oil droplets or the concentration of thickening agents. 

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