Controlled release

Controlled or targeted release is the most common apphcation of microcapsules. Microencapsulation is an ideal tool to effect and achieve a desired delay of the active core until the correct stimulus is encountered. Most microcapsules are extraordinarily stable and show a great retardation of the encapsulated substances. Fragrances, aromas, drugs, enzymes, cosmetics and even pharmaceutical formulations (vitamins, drugs) are encapsulated for delivery from textiles at a specific time, rate, or situation. The encapsulated substances can either be released at once 

Microcapsules are also used to store volatile or unstable substances on a temporary basis. The active agents in these capsules are usually not suitable for their direct use, due to a variety of reasons including low solubility, reactivity (may be too low or too high) and stability (low). On the other hand, it may be advantageous to optimize the properties of the active agents, for example by using sustained or controlled release functions. 

Microencapsulation for protective purposes is equally important as the controlled release uses, as microcapsules may prevent the possible premature loss of an active ingredients, which is reflected in a decline of its activity. 

Microencapsulation is an effective and longlasting method of protecting unstable or reactive products against external influences such as oxidation, alkalinity, acidity, heat, polluting gases, moisture and evaporation, and in this way it can be used to increase the shelf life of a product. Microencapsulation prevents unwanted 

Little will be said abont controlled release flavorings in this chapter simply because there is limited space. However, there is substantial interest in imparting controlled release properties to encapsulated flavorings. Ideally, the flavoring would be protected from the environment until the final product is ready for consumption. Unfortunately, there are limited opportunities for imparting controlled release to flavorings due to both materials limitations (FDA approved) and cost considerations — cost of both materials and processing. 

Encapsulated flavorings currently made generally use water as a manufacturing vehicle, and thus water (hydration) is the release mechanism. However, coacervation (when cross-linked) produces an insoluble wall, and thus release is via diffusion as opposed to dissolution. In high moisture systems, this slows release but does not stop it. The extrusion process also may provide some controlled release properties in that one may use less soluble matrices thereby reducing release rates. 

A wide array of manufacturing processes is available for the production of dry flavorings. Each of these processes results in a product that has unique strengths and weaknesses. The ultimate choice of process depends upon cost and performance needs. 

Fischetti, F. Workshop in Food Flavors Creation and Mannfactnring, offered at the Dept, of Food Science and Nntrition, University of Minnesota, St. Panl, May 2002. 

Reineccius, Beverage emulsions and the utilization of gum acacia as emulsifier/stahilizer, Perfum. Flavorist, 25, 4, p. 24, 2000. 

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Phospholipid molecules form bilayer films or membranes about 5 nm in thickness as illustrated in Fig. XV-10. Vesicles or liposomes are closed bilayer shells in the 100-1000-nm size range formed on sonication of bilayer forming amphiphiles. Vesicles find use as controlled release and delivery vehicles in cosmetic lotions, agrochemicals, and, potentially, drugs. The advances in cryoelec-tron microscopy (see Section VIII-2A) in recent years have aided their characterization [70-72]. Additional light and x-ray scattering measurements reveal bilayer thickness and phase transitions [70, 71]. Differential thermal analysis... 

CONTROLLED RELEASE TECHNOLOGY - PHARMACEUTICAL] pol 7) Androsta-l,4-diene-3,17-dione [63-05-8]... 

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