Creaming fraction

Concentration. Tea extracts are generally concentrated under vacuum to the soHds content desired for drying. Ereeze concentration has been described (99), as has reverse osmosis (qv) (100). Preserved aroma and the solubiHzed cream fraction may be added before drying. 

Sundheim, G., Bengtsson-Olivecrona, G. 1985. Lipolysis in milk induced by cooling or by heparin comparisons of amount of lipoprotein lipase in the cream fraction and degree of lipolysis. 1. Dairy Sci. 68, 589-593. 

Milk Products. Cardboardy or metallic or tallowy flavors resulting from oxidative changes in the cream fraction of cows milk are distasteful in fluid milk and dairy products. These flavors develop more intensely in certain lots of fluid milk when the cows are fed dry rations. 

As shown in Table 3.2, neutral lipids form the major groups of natural rubber lipids. Typically, a whole natural rubber latex contains 54% neutral lipids, 33% glycolipids, and 14% phospholipids. The lipids, such as phospholipids, adsorbed on the surface of rubber particles are normally found in the cream fraction. The rubber particles in the skim latex, on the other hand, have a very low level of adsorbed lipids. " Smoking, a process used to dry natural rubber, has been found to increase the amount of lipid extract significantly but to decrease the free fatty acid content. ... 

Although it is hard to draw a sharp distinction, emulsions and foams are somewhat different from systems normally referred to as colloidal. Thus, whereas ordinary cream is an oil-in-water emulsion, the very fine aqueous suspension of oil droplets that results from the condensation of oily steam is essentially colloidal and is called an oil hydrosol. In this case the oil occupies only a small fraction of the volume of the system, and the particles of oil are small enough that their natural sedimentation rate is so slow that even small thermal convection currents suffice to keep them suspended for a cream, on the other hand, as also is the case for foams, the inner phase constitutes a sizable fraction of the total volume, and the system consists of a network of interfaces that are prevented from collapsing or coalescing by virtue of adsorbed films or electrical repulsions. 

Fig. 4.5.16 Schematic drawing of a boundary layer mixing mechanism. It is proposed that a thin layer with thickness 8 has a linear velocity profile with average velocity V/2. Material with bulk droplet volume fraction ( >in is drawn into the creamed layer (area Ac) and material with average creamed layer volume fraction (j)ou, is swept out. The remainder of the emulsion (inside the dashed circle) is stagnant.

Instant tea produced as described above will dissolve completely in hot water but not in cold water, as the caffeine-polyphenol complexes are insoluble under those conditions. Since virtually all instant tea manufacture in the U.S. is for iced tea preparation, process modification is required. This initial extract may be cooled to 5 to 10°C and the cold water insoluble material or cream be allowed to precipitate. Under these conditions, 20 to 35% of the extract solids may be separated by centrifugation. The supernatant solids will reconstitute in cold water after concentration and drying.105 It is also possible to process the cream to make a portion of it compatible with the product and thereby retain the caffeine and some polyphenolic components that are present in this fraction.106 Commercial use of the enzyme Tannase, which removes gallic acid from gallated tea polyphenols107 and reduces cream formation108 can be used to reduce cream losses and manufacture instant teas retaining more of the natural polyphenol content. 

Formulators can use the tendency of creams, gels, and other systems to evaporatively concentrate to advantage. Solvents are chosen and blended so that the drug remains soluble in the formed film long after application is made. This can be accomplished by replacing a fraction of the water or other highly volatile solvent found in these systems with solvents of far lower volatility. As previously pointed out, 5-15% propylene glycol is found in many topical corticosteroid creams and lotions just for this reason. 

The most widely studied deformable systems are emulsions. These can come in many forms, with oil in water (O/W) and water in oil (W/O) the most commonly encountered. However, there are multiple emulsions where oil or water droplets become trapped inside another drop such that they are W/O/W or O/W/O. Silicone oils can become incompatible at certain molecular weights and with different chemical substitutions and this can lead to oil in oil emulsions O/O. At high concentrations, typical of some pharmaceutical creams, cosmetics and foodstuffs the droplets are in contact and deform. Volume fractions in excess of 0.90 can be achieved. The drops are separated by thin surfactant films. Selfbodied systems are multicomponent systems in which the dispersion is a mixture of droplets and precipitated organic species such as a long chain alcohol. The solids can form part of the stabilising layer - these are called Pickering emulsions. 

Therein lies the secret of the diversity of protein functions. There are so many possible protein structures that nature, through the process of evolution, has been able to pick and choose among this cornucopia of possibilities to find the cream of the cream for each function. The number of different proteins in the human body— perhaps 100,000—is an incredibly small fraction of all the proteins that one can construct using 20 natural amino acids linked in chains, say, 100 units long (1 part in 10 ). 

Another technique consists of submitting the emulsion to centrifugation and determining the droplet volume fraction < / at the top (bottom) of the cream (sediment). The centrifugation typically takes several hours until the equilibrium volume fraction is achieved. After equilibration, if the droplets occupy a distance much less than that of the centrifuge lever arm, the spatial gradient in the acceleration can be neglected, and the osmotic pressure can be determined (see Fig. 4.1) ... 

H.M. Princen, M.P Aronson, and J.C. Moser Highly Concentrated Emulsions. II Real Systems. The Effect of Film Thickness and Contact Angle on the Volume Fraction in Creamed Emulsions. J. CoUoid Interface Sci. 75, 246 (1980). 

The crysts of TNT in cast expls may vary from microscopic size to a substantial fraction of the size of the charge, depending upon casting conditions and procedure. The approach known as cream casting results in very fine crysts. In mixed expls, which usually are cast in the form of slurries, the solid particles tend to inhibit cryst growth, although TNT crysts sometimes apparently grow around the particles of the slurry. The effects of particle size on initiation sensitivity, failure diameter, and performance characteristics also have been observed to apply to crystal size in cast TNT... 

An experimental study was performed to determine the applicability of the theory. Oil-in-water (o/w) emulsions, stabilised with anionic surfactants, were prepared, with known quantities of added electrolyte, and were creamed by either gravitation or centrifugation. The results can be summarised as follows at low electrolyte concentrations, where h would have a finite value, <(> was less than 0.74. Over a range of concentrations, where it was assumed that both 0 and h were negligible, = 0.74 ( 0.02). The emulsions were found to be polydis-perse, so this did not appear to affect the volume fraction to a great extent. In addition, < > was found to be independent of the method of cream formation. 

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