Definition And Technology Development

Encapsulate is most commonly defined in its verb form as the act of enclosing or when used as a noun, it is synonymous with capsule. Microencapsulate applies to enclosure, or encasement in microcapsules.

Terms that are often used interchangeably with encapsulate are coated, or protected, eg, coated leavening, protected salt, and coated acids. All three terms are used when referring to practically any core material that is encased or enclosed in an outer shell. However, there are subtle distinctions that often dictate which term is more properly used. Very small capsules, perhaps 100 fi and less, are practically always called capsules or microcapsules. The adjectives coated or protected usually imply a cheaper, more crudely manufactured capsule. Coated or protected particles are generally larger than 100 //.

In the late 1800s a pharmacist named Upjohn patented a process still referred to as pan coating (1). Relatively large solid particles were tumbled in a cylindrically shaped mixer as liquid coating material was sprayed on. Typically a sugar in water solution was the liquid used and the process involved alternately spraying and evaporating water, until through deposition of sugar, the rounded polished capsules achieved the desired size, shape, and shell thickness. The process was originally applied to drugs and pharmaceuticals for the purpose of taste masking—sugar coated pills—and is still being used extensively. Its application has expanded into several well-known brands of candies and confections.

Most texts establish pioneer work in microencapsulation as having been done in the 1930s by the National Cash Register Company (Dayton, Ohio) (2). Using a chemical process often termed coacervation, National Cash Register developed a means of occluding a colorless dye in a cross-linked gelatin shell. The particles were deposited (less than 20 fi in a cross section) in a thin layer on the underside of a sheet of paper in contact with a second sheet impregnated with a colorless reagent. Pressure exerted on the laminate by the point of a pen or pencil fractured the microencapsulate releasing the reagent-sensitive dye, producing a colored image. The process, which became commercial in 1954, produced the world's first carbonless duplicating paper. In 1981 production of carbonless copy business forms exceeded 500,000 tons per year (3,4).

The National Cash Register invention and the new coacervation process created interest during the mid-1950s in encapsulation in a wide variety of fields from agriculture to cosmetics and toiletries, from electronic parts to food processing (5). The coacervation process itself was examined and, for some applications, was found technically suitable and economical. For many others, of the myriad potential uses that were conceived, coacervation had technical limitations and was much too costly. However, the interest in coacervation spawned development of new encapsulation technologies; some of which have been found entirely suitable for food ingredient applications.

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