Rheology foodstuffs

An understanding of non-Newtonian behaviour is important to the chemical engineer from two points of view. Frequently, non-Newtonian properties are desirable in that they can confer desirable properties on the material which are essential if it is to fulfil the purpose for which it is required. The example of paint has already been given. Toothpaste should not flow out of the tube until it is squeezed and should stay in place on the brush until it is applied to the teeth. The texture of foodstuffs is largely attributable to rheology. 

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). 

There are at least two aspects of slip that are of fundamental importance to food rheology as they provide important processing and textural information for foodstuffs. These are ... 

These are early days in the development of extensional rheometers for foods and in our understanding of the extensional rheology of foodstuffs. The lack of commercial availability of extensional rheometers could be stalling the application of extensional rheology in characterizing products and processing operations in the food industry. For industrially important food products, product specific rheometers may need to be developed. 

Davis, S.S. 1973. Rheological properties of semi-solid foodstuffs. J. Text. Stud. 4, 15-40. 

Shama, F., Sherman, P. 1968. An automated parallel-plate viscoelastometer for studying the rheological properties of solid food materials. In Rheology and Texture of Foodstuffs. S.C.I. Monograph No. 27, pp. 77-90, Society of Chemical Industry, London. 

Higgs, S.J., Norrington, R.J. 1971. Rheological properties of selected foodstuffs. Proc. Biochem. 6, 52-54. 

Figure 8-1 Interrelationships in Texture Studies. Source From P. Sherman, A Texture Profile of Foodstuffs Based upon Well-Defined Rheological Properties, J. Food Sci., Vol. 34, pp. 458-462, 1969.

Sherman, P. 1969. A texture profile of foodstuffs based upon well-defined rheological properties. J. Food Sci. 34 458-462. 

Vasic, I., and J.M. deMan. 1968. Effect of mechanical treatment on some rheological properties of butter. In Rheology and texture of foodstuffs, 251-264. London Society of Chemical Industry. 

Suspensions or dispersions of particles in a liquid medium are ubiquitous. Blood, paint, ink, and cement are examples that hint at the diversity and technological importance of suspensions. Suspensions include drilling muds, foodstuffs, pharmaceuticals, ointments and cremes, and abrasive cleansers and are precursors of many manufactured goods, such as composites and ceramics. Control of the structure and flow properties of such suspensions is often vital to the commercial success of the product or of its manufacture. For example, in consumer products, such as toothpaste, the rheology of the suspension can often determine consumer satisfaction. In ceramic processing, dense suspensions are sometimes molded (Lange 1989) and then dried and sintered or fired into optical components, porcelin insulators, turbine blades, fuel cells, and bricks (Rice 1990 Simon 1993). Crucial to the success of the processing is the ability to transform a liquid, moldable suspension into a solid-like one that retains its shape when removed from the mold. These examples could be multiplied many times over. 

De Kee, D. Turcotte, G. Code, R.K. Rheological characterisation of time-dependent foodstuffs. In Rheology Volume 3 Applications Astarita, G., Marrucci, G., Nicolais, L., Eds. Plenum Press New York, 1980 609-614. 

Technologically required functional effects can also be achieved by intentionally employing various food additives — food colors, sweeteners, and a host of other compounds — that are not regarded as foodstuffs per se, but are used to modify the rheological properties or acidity, increase the color stability or shelf life, or act as humectants or flavor enhancers (Rutkowski et al., 1997). 

Prentice, J. H. "Measurements in the Rheology of Foodstuffs", Elsevier Applied... 

The rheological properties of foodstuffe are important in food process engineering since they are the essential parameters in plant design (pumping requirements, pipe and valve dimensions, and mixing operations, etc.) and in the calculation of basic heat, mass, and momentum transfer (Szczesniak, 1977). 

In sensory evaluation consumers estimate fruit firmness on the basis of the deformation resulting from physical pressure applied by the hand and fingers. The toughness or tenderness of meat is subjectively evaluated in terms of the effort required for the teeth to penetrate and masticate the flesh tissues. Therefore, determination of rheological properties of foodstuffs is important in evaluation of consumer-determined quality by correlating rheological measurements with sensory tests. 

The extension of these principles to molecules and macromolecules based on renewable resources has been applied to polymer chemistry and technology, mostly in two areas requiring viscous materials, namely (i) the preparation of liquid polyols to be used in the manufacture of polyurethanes, and (ii) the synthesis of macromol-ecular rheology modifiers. A typical polyol for the synthesis of polyurethane foams is obtained industrially from the oxypropylation of sorbitol, [3] whereas hydroxypropyl cellulose represents a major commodity for the rheological control of paints, foodstuff, cosmetics, etc. [4]. 

Rheology is the study of flow of matter and deformation and these techniques are based on their stress and strain relationship and show behavior intermediate between that of solids and liquids. The rheological measurements of foodstuffs can be based on either empirical or fundamental methods. In the empirical test, the properties of a material are related to a simple system such as Newtonian fluids or Hookian solids. The Warner-Bratzler technique is an empirical test for evaluating the texture of food materials. Empirical tests are easy to perform as any convenient geometry of the sample can be used. The relationship measures the way in which rheological properties (viscosity, elastic modulus) vary under a... 

Almost all agricultural aud industrial products, especially foodstuffs, contain colloidal structures that determine their rheological properties and textures. Manufacturers must control these structures in order to provide their products with... 

Polymers are probably best known for their use as bulk materials, as discussed in the previous section. However, they also play an important role in the control of solution and dispersion rheology. This apphcation includes fields as diverse as fuels, lubricants, water treatment chemicals, foodstuffs, and cosmetic formulations. In these areas polymers affect the flow behavior, and thereby the performance, of a fluid during and after application. When one attempts to dissolve a polymer in solvents selected at random, many, per-... 

Food texture and viscosity. Bourne M.C, 1994, Academic Press, 85 Measurements in the Rheology of foodstuffs, Prentice J. H, Chapman HaU, 1984, 59 Rheological methods in food process engineering, Steffe J. F, Freeman Press, 1992, 65 Rheology of Fluids and Semisolid Foods Principles and Applications, Rao M.A, Aspen Pub., 1999, 125.00... 

Spray drying is the key process step in the production of powdery foodstuffs. For cost reductiOTi and improved yield, it is favorable to decrease the water content of the feed, thereby increasing its sohd fraction. Single- or multiphase feeds may be used, the latter of which often show a complex rheological behavior. At increased viscosity of the feed due to a higher solid content atomization is more difhcult to achieve with COTiventional pressure atomizers. At higher viscosities, the use of pneumatic atomizers would be beneficial however, they are often avoided due to their high gas consumption. 

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