Plastic fats

Most of the methods used to characterize the rheological behavior of butter are empirical and attempt to imitate certain sensory perceptions. They typically involve penetrometry, extrusion or sectility tests (Prentice, 1972). In these tests, the structure of the material is destroyed in order to probe its response to an applied stress or deformation. These methods mostly serve a quality control function. Their results provide an index of consistency to adjust milk-blending operations or to regulate a step in the butter-making process. While the results have practical significance, they often have no theoretical basis. Therefore, attempts have also been made to study the intrinsic properties of plastic fats. In many such cases, small deformation tests, in which the structure of the sample remains intact have been used to probe milk fat rheology. 

Figure 7.8. Typical creep curve for a plastic fat. A instantaneous deformation upon loading B instantaneous sample recovery upon unloading C time-dependent recovery of sample D permanent sample deformation (adapted from deMan and Beers, 1987).

The typical creep curve for a plastic fat is shown in Figure 7.8 and demonstrates the effect of working on the structure of butter. The softening that occurs in plastic fats is dependent on both the amount of force or deformation applied and also on the testing time (deMan and Beers, 1987). When a force is applied (i.e., when the sample is compressed), there is an initial elastic response (A), which can be represented by a Hookean spring (deMan et al., 1985 deMan and Beers, 1987). If the yield stress is exceeded,... 

For a plastic fat, the yield stress was defined as the stress at the limit of linearity in a small deformation rheological test. Agreement between theory and experiment was found to be good. 

Vasic, I., deMan, J.M. 1967. Measurement of some rheological properties of plastic fats with an extrusion modification of the shear press. J. Am. Oil Chem. Soc. 44, 225-228. 

VandenTempel, M. 1958. Rheology of plastic fats. Rheol. Acta 1 115-118. 

The theory of bond formation between the crystal particles in plastic fats needs revision. Recently, it has been proposed that a process of sintering —the formation of solid bridges between fat crystals—occurs during... 

Many interrelated factors influence the texture of plastic fats. Fatty acid and glyceride composition are basic factors in establishing the properties of a fat. These factors, in turn, are related to solid fat content, crystal size and shape, and polymorphic behavior. Once the crystal network is formed, mechanical treatment and temperature history may influence the texture. 

The network systems in plastic fats differ from those in protein or carbohydrate systems. Fat crystals are embedded in liquid oil and the crystals have no ionized groups. Therefore, the interactive forces in fat crystal networks are low. The minimum concentration of solid particles in a fat to provide a yield value is in the range of 10 to 15 percent. 

DeMan and Beers (1987) have reviewed the factors that influence the formation of three-dimensional fat crystal networks. The fat crystal networks in plastic fats (Figure 8-44) are highly thixotropic, and mechanical action on these products will result in a drastic reduction of hardness. 

Marangoni, A.G., and Rousseau, D. (1996). Is plastic fat rheology governed by the fractal geometry of the fat crystal networks. Journal of American Oil Chemists Society. 73 993-994. 

Fermentation is also used to treat industrial chemical or organic waste. The principle is very similar to the described anaerobic sludge treatment. That means that the organic material is converted to methane. Examples include waste containing cotton, rubber, plastics, fats, explosives, and detergents. The waste can be transferred to special treatment plants or be treated in situ in the open field where the waste was buried. Open-field microbiological treatment of spills or deposits of hazardous chemicals is a potentially attractive and inexpensive remediation method and has attracted a lot of research attention. So far, however, only a few examples have been successful. 

Solid Fat Content and the Fat Crystal Network The solids content of a fat crystal network is of critical importance to the final physical properties of the system. Generally, an increase in SFC leads to an increase in fat firmness. The SFC measurement has been widely used as a determinant quantity for the structural properties of fat systems. Estimations for commercial plastic fats, including butter, predict firmness increases of 10% for every percent increase in SFC (45). As a result, models used to describe the rheological properties of fats incorporate references to SFC values. 

Winterized rice bran oil is an acceptable oil for salad dressing and mayonnaise. The hard fraction of rice bran oU may be used to replace the plastic fats in margarines and shortening. Hydrogenated rice bran oil is adaptable to specialty shortenings and margarines. 

The supercooled stream from the A unit flows directly to the worker unit. There is normally a 5-8°C (10-15°F) temperature rise across the B unit most of which results from latent heat of crystallization mechanical power does not add significantly to the total heat input. The plasticized fat from the B unit is forced through a special extrusion valve that also maintains an internal pressure of 17-20 bar... 

In the past, for reasons related to both history and climate, there were distinct geographical divisions of people by fat- and oil-consuming groups. Inhabitants of central and northern Europe derived most of their lipids from domestic animals. Consequently, the food habits and cuisine of these people developed around the use of plastic fats. On the... 

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