Micelles, frozen

This technique does not, however, overcome the formation of frozen micelles due to the formation of glassy cores at a specific nonselective solvent/selective solvent composition. Polydisperse micelles can also be generated during this preparation process if the starting material is characterized by a composition or MW polydispersity. In this respect, micelles will be first formed by the chains containing the larger insoluble block during the addition of the selective solvent. 

It has been shown that block copolymer micelles are dynamic structures, although they can be kinetically frozen. Unimers can thus escape from micelles and be exchanged with other micelles or be adsorbed on another interface... 

Extent of mixing is related to time since mixing requires sufficient time to allow the polymer chains to mix. Thus, for miscible blends particular structures can be frozen-in by rapid cooling when the desired mixing is achieved. Here, micelles of particular structures can cause the mixture to perform in one manner governed by the particular grouping that may not occur if more total mixing occurs. 

Principal micelle characteristics. The structure of the casein micelles has attracted the attention of scientists for a considerable time. Knowledge of micelle structure is important because the stability and behaviour of the micelles are central to many dairy processing operations, e.g. cheese manufacture, stability of sterilized, sweetened-condensed and reconstituted milks and frozen products. Without knowledge of the structure and properties of the casein micelle, attempts to solve many technological problems faced by the dairy industry will be empirical and not generally applicable. From the academic viewpoint, the casein micelle presents an interesting and complex problem in protein quaternary structure. 

Most food products and food preparations are colloids. They are typically multicomponent and multiphase systems consisting of colloidal species of different kinds, shapes, and sizes and different phases. Ice cream, for example, is a combination of emulsions, foams, particles, and gels since it consists of a frozen aqueous phase containing fat droplets, ice crystals, and very small air pockets (microvoids). Salad dressing, special sauce, and the like are complicated emulsions and may contain small surfactant clusters known as micelles (Chapter 8). The dimensions of the particles in these entities usually cover a rather broad spectrum, ranging from nanometers (typical micellar units) to micrometers (emulsion droplets) or millimeters (foams). Food products may also contain macromolecules (such as proteins) and gels formed from other food particles aggregated by adsorbed protein molecules. The texture (how a food feels to touch or in the mouth) depends on the structure of the food. 

The major defect, which limits exploitation of frozen milk concentrates as consumer products, is the instability of the casein micelle system (Keeney and Kroger 1974 Morr 1975). The casein micelles gradually destabilize during storage of the frozen milk concentrate. 

Several compositional and processing variables affect the physical stability of the casein micelles in frozen milk concentrates. These factors include pH, mineral composition, total solids content, forewarming treatment, homogenization and fat content, freezing rate, storage temperature, and fluctation of storage temperature (Keeney and Kroger 1974 Webb 1970). 

The physical stability of the casein micelle system is closely related to the degree of lactose crystallization from the unfrozen phase of the frozen concentrate. Crystallization of lactose from the unfrozen solution temporarily raises its freezing point, causing additional water to freeze, thus increasing the concentration and promoting destabilization of casein micelles. 

Transmission electron micrography has, remarkably, been successfully used to image micelles formed by block copolymers in dilute solutions. Price and coworkers used two preparation methods. In the first method (Price and Woods 1973), f reeze etching, a drop of solution was rapidly frozen by quenching in liquid nitrogen. Solvent was then allowed to evaporate from a freshly microtomed surface of the droplet. Finally, a replica was made of collapsed micelles raised proud from the frozen surface. In the second method (Booth et al. 1978), a drop of micellar solution was allowed to spread and evaporate on a carbon substrate, and 0s04 was used to selectively stain one of the blocks. 

The relaxation behaviour of water can be quite different from bulk water if it is enclosed in reversed micelles (Wong et al., 1977), or bound to frozen erythrocytes (Zipp et al., 1976), or bound to red-cell membranes (Finch and Schneider, 1975). 

PBS and gently blotted to remove blood and tissue fluids, then suspended over the lip of a small (250 pi) microcentrifuge tube and punctured with a needle to allow the bile to drain into the tube. Store frozen until assay. There is usually enough material to measure lipid composition (bile acids, cholesterol, phospholipids) with standard colorimetric kits (<1 pi needed for each assay). In addition to biliary cholesterol levels, it is important to take note of bile salt concentrations, since these are the detergents which suspend dietary lipids in micelles and deliver them to the intestinal epithelium for absorption by enterocytes. Differences in bile salt concentration alone could lead to differences in cholesterol absorption. 

In cryoelectron microscopy, the micelles can be examined in the frozen hydrated state without staining. Van Bruggen etal. (1986) in a preliminary report, showed micrographs of particles with a type of substructure similar to that seen by other methods (Fig. 12d). 

The resulting micellar aggregates resemble, in most of their aspects, those obtained with classical low molecular weight surfactants, but the nonergodicity of BCs allows the preparation of many different kinetically frozen morphologies. From the initial basic observations of micelle formation by Merret in 1954 [24] to the last structures of living micelles obtained by Winnik and co-workers in 2007... 

Association Structures. The onset of micellization was observed using light-scattering data and confirmed by electron microscopy of carbon replicas from freeze fracturing of samples frozen to — 150°C. The light-scattering unit was a Sophica Photo Gonia Diffusometer, Model... 

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