Physical Chemistry of Foods

FIGURE9.1 Example of the structure of (a) ice cream mixþair, and (b) the ice cream made of it (at about
58 C). The fat globules ...

present. This illustrates the other point made: structure and properties depend on the history (process steps applied, storage c ...

distances. The physical building blocks of such a system may be called structural elements, i.e., regions that are bounded by a ...

net result always depends on the distance over which they are acting. This is discussed in Chapter 3 and is further worked out i ...

irreversible, systems. It may further be noted that dispersions are called colloidsif the particles are larger than most molecul ...

interaction forces between the particles; and (c) the possibility of loss of substances by evaporation, etc. An oil-in-water emu ...

TABLE9.2 Approximate Values of Some Physical Constants of Oil (i.e., a Liquid Mixture of Triacylglycerols), Water, a Saturated S ...

Figure 9.1b gives an example of a complicated structure. Ice cream can contain seven or more different structural elements, maki ...

Order. For very small volume fraction j, the particles in a dispersion can be distributed at random. For higherj, there is alway ...

Optical anisotropy. The best known example is that where the refractive index depends on direction. Such a material is said to b ...

FIGURE9.4 Structure of an apple or, more precisely, of some small parts of an apple, at various scales. Highly simplified and sc ...

9.2 IMPORTANCE OF SCALE For homogeneous systems, knowledge of properties and phenomena on a molecular ormicroscopicscale often s ...

9.2.1 Geometric Aspects Thenumberof particles present per unit volume (N) is, for a given volume fraction (j), inversely proport ...

by x¼ d 6 1 j
1 jmax  ð 9 :1bÞ wherejmaxequals, for instance, 0.7. Results for both equations are in Figure 9.6, and it is s ...

transport rates through the system (Section 5.3) and capillary phenomena (Section 10.6). The pore size is governed by the same v ...

small particles, external stresses are unlikely to overcome internal forces, while this may be easy for large particles. Gels ma ...

In most cases, we are interested in the relative refractive indexm, i.e., the ratio of the refractive indices of the materials o ...

dis much smaller than the wavelength (Rayleigh scattering), the amount of light scattered by each particle is about proportional ...

which can thus pass the emulsion almost unscattered. For still larger particles, the dependence of scattering onlis very small, ...

wavelengths, the resulting color can roughly be predicted. Furthermore, the rules of thumb on whiteness given above can be of so ...