Particles in homogenized milk

Michalski et al. (2002) studied the types of particles in homogenized milk and identified three classes ... 

The particles in homogenized milk showed similar electrophoretic properties to casein micelles despite the... 

The functional properties of the particles in homogenized milk also require better definition. It is only partly evident how instability develops in the larger particles, but the problem of the conformation of the stabilizing entities in the particles remains. Definition of an adequate model of the complex fat/casein particles in the milk is still to be achieved, and until this is done there seems to be little chance of understanding the complex behaviour of this material. 

Figure 3 Average diameters of particles in homogenized milk, as a function of the number of passes through the homogenizer (Mi-crofluidizer), and the pressure. Diamonds and filled line homogenization pressure of 14 MPa squares and broken line pressme of 21 MPa triangles and full Une pressure of 28 MPa circles and broken hne pressure of 35 MPa.

The structure of the interfacial layers in food colloids can be quite complex as these are usually comprised of mixtures of a variety of surfactants and all are probably at least partly adsorbed at interfaces which even individually, can form complex adsorption layers. The layers can be viscoelastic. Phospholipids form multi-lamellar structures at the interface and proteins, such as casein, can adsorb in a variety of conformations [78]. Lecithins not only adsorb also at interfaces, but can affect the conformations of adsorbed casein. The situation in food emulsions can be complicated further by the additional presence of solid particles. For example, the fat droplets in homogenized milk are surrounded by a membrane that contains phospholipid, protein and semi-solid casein micelles [78,816], Similarly, the oil droplets in mayonnaise are partly coated with granular particles formed from the phospho and lipo-protein components of egg yolk [78]. Finally, the phospholipids can also interact with proteins and lecithins to form independent vesicles [78], thus creating an additional dispersed phase. 

HOMOGENIZING. A pr. icess fur teducing the size of particles in u liquid and useful in the preparation of numerous fond substances, including milk, ice cream, salad dressings, various fruit juices. Ilavor concentrates, infant foods, among others. 

Particles in a suspension are much larger than atoms. In contrast, particles in a solution are atomic-scale in size. A heterogeneous mixture of intermediate size particles (between the size of solution particles and suspension particles) is a colloid. Colloid particles are between 1 nm and 1000 nm in diameter. The most abundant substance in the mixture is the dispersion medium. Milk is a colloid. Although homogenized milk resembles the cornstarch mixture in Figure 15-19a, you cannot separate its components by settling or by filtration. 

Martin also has a word about the harm from the use of homogenized milk, as per the work of cardiologist Kurt Oster, M.D., of Fairfield University. Thus, natural milk contains xanthine oxidase, an oxidizing enzyme, in large particles, which, consequently, do not get into the bloodstream. Homogenization reduces the particle size, allowing entry into the bloodstream, which Oster claims is harmful to the vascular system. 

Two forms of the casein proteins are used to stabilize oil/Water emulsions. Most siirply, a mixture of the proteins (as in sodium caseinate), or the individual proteins themselves, allows the formation thin layers, if not monolayers, of protein at fat/Water interfaces (1). By contrast, in preparations such as homogenized milk, the entities which bind to and stabilize the fat/Water interface are much larger and more complex, and may be considered as intact or semi-intact casein micelles (2). These particles are highly aggregated complexes of the four caseins ... 

Colloids are characterized according to the state (solid, liquid, or gas) of the dispersed phase and of the continuous phase. Table 12.4 lists various types of colloids and some examples of each. Fog and smoke are aerosols, which are liquid droplets or solid particles dispersed throughout a gas. An emulsion consists of liquid droplets dispersed throughout another liquid (as particles of buttofat are dispersed through homogenized milk). A sol consists of solid particles dispersed in a liquid. 

Size of the Particles. — The suspended globules of caoutchouc found in the latex vary in rize within comparatively wide limits. Those of Hevea have been found by Fickendey to have a diameter of 0.5-2.5iu. On the other hand, few particles in the latex of Funtumia have a diameter as great as O.Im, and the milk appears almost homogeneous under the most powerful microscope. 

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