Humectant system

Toothpaste contains an abrasive (qv), flavor, a humectant system, a surfactant, a binding and thickening agent, color, and one or more therapeutic or cosmetic agents. 

Gels. Amorphous hydrated silicas of a purity and stmcture typical of those used ia type 1 dentifrices and the liquid portion (humectant system) of type 1 dentifrices both have approximately the same refractive iadex, ie, about 1.47. As a result, the type 1 dentifrices represented ia Table 1 are inherently transparent or translucent. In the marketplace it has become popular to refer to such dentifrices as gels. For marketing reasons some companies have chosen to opacify these products, with titanium dioxide, for example. The opacified products are identical ia functionality, stmcture, and all other ways, except opacity, to their translucent or transparent counterparts. 

Humectant System The humectant system comprises one or more liquids in which the other toothpaste ingredients are dispersed to provide a stable paste. The liquids are usually glycerol and 70% aqueous sorbitol. Propylene glycol [57-55-6] and polyethylene glycols are used occasionally. The liquids are used alone or in combination. Their water activity is such that they do not support bacteriological growth. The humectant system does not crystallize, and thus the final formulation does not dry out or cause the tube cap to lock to the nozzle. 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Propylene glycol is also an effective humectant, preservative, and stabilizer and is found in such diverse apphcations as semimoist pet food, bakery goods, food flavorings, salad dressings, and shave creams. Humectancy, or the capabiUty of retaining moisture in a product, is a result of the vapor—Hquid equihbria of the glycol—water system and can be estimated from tables provided by suppHers (27). 

During the last lew years, important research has gone into the addition of multiple humectants and water to food systems. Studies have shown that a hysteresis effect may occur with certain humectants. i.e, a different rate of moisture absorption than the rate for moisture desorption. Multiple humectants tend to compensate these hysteresis effects, giving uniform rates in both directions. 

The effect of several humectants is for each to sequester an amount of water independently of the other humectants that may be present in the food. Each thus lowers the water activity of the system according to the equation of Ross (1975) ... 

NEB and almost all chemical reactions in foods are thought to cease in systems that are below a of 0.23 to 0.43, the typical range of the moisture monolayer value (Labuza et al., 1969 Rockland and Nishi, 1980). In Figure 20.5b, this trend appeared as expected for the control formulation, which contained no humectant. However, upon the addition of hydrophilic glycols as humectants (which were liquids at the test temperature and thus miscible in water), the at which the maximum reaction rate occurred shifted to a much lower value. Propylene glycol showed a maximum rate at a of about 0.2, with a rate equal to the maximum rate of the control at a a of 0.8. 

The effects of water on the destruction of the protective food structure in some specific dehydrated foods is probably involved in prevention of lipid oxidation in heated meat systems (Karel, 1986). In systems in which there are both surface lipids and lipids encapsulated within a carbohydrate, polysaccharide, or protein matrix, the surface lipids oxidize readily when exposed to air. The encapsulated lipids, however, do not oxidize until the structure of the encapsulated matrix is modified and/or destroyed by adsorption of water as shown by Simatos and Karel (1988). In some IM meats, muscle may be considered as being encased in or surrounded by a humectant matrix. However, free lipid may be left on the surfaces. The unwarranted overuse of lipids, which often happens in the indirect drying process to improve heat transfer and to prevent burning, is detrimental to the products. Prevention of this structural change is of considerable... 

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