7. Encapsulation and release

Many food products whose development was thought to be technically unfeasible are possible today because of the wide availability of encapsulated ingredients. Such ingredients are products of a process that totally envelopes the ingredient in a coating or 'capsule' thereby conferring many useful and otherwise unusual properties to the original ingredients.

Encapsulation is a technique that is applied to preserve and/or protect numerous ingredients. In the flavour industry, the encapsulation process is used chiefly to convert liquid flavour materials to free-flowing, dried powdered products. It can also be used effectively to separate and/or isolate reactive materials, provide protection for a compound or formulation, and control the release of material during food application (Bakan, 1978).

In a broad sense, encapsulation technology includes the coating of minute particles of ingredients (e.g., acidulants, fats, and flavours) as well as whole ingredients (raisins, nuts, and confectionery products), that may be accomplished by microencapsulation and macro-coating techniques, respectively.

Microencapsulation is defined as a technology of packaging solids liquids or gaseous materials in miniature, sealed capsules that can release their contents at controlled rates at specific conditions. The miniature packages, called 'microcapsules', may range from sub- micron to several millimetres in size and are ideally spherical; however, their shape is heavily influenced by the structure of the unencapsulated material. In the encapsulate, the active portion is termed the core, internal phase, or fill. The encapsulating material is called the shell, coating, or wall material and may range in both its thickness and number of layers. Flavours are encapsulated for a number of reasons. One of the most important is to retain them in a food product during storage. Flavours are volatile and thus would readily evaporate from a food matrix during storage.

A second reason is to protect the flavour from undesirable interactions with the food. While there are numerous examples in the literature, the most extreme case of flavour/food interaction is chewing gum. Adding liquid flavours to the chewing gum results in substantial losses of flavour of the gum base. This flavour is not recovered during the chewing and is therefore lost. The use of encapsulated flavouring in gums will reduce flavour needs by nearly 50%.

A third reason is to minimise flavour/flavour interactions. If the flavour contains reactive constituents (e.g. aldehydes and amines which would form Schiff's bases), the flavour could be divided in two parts, and containing the aldehydes and the other the amines. Each could then be encapsulated separately and blended into the finished dry food product.

A fourth reason is to guard against either light-induced reactions or oxidation. Oxidation is a major mode of product failure when the flavour contains citrus oils.

A fifth reason, a relative new application of encapsulation techniques, is to effect the controlled release of the flavour. The use of creative encapsulation for the controlled release of flavours will be on the increase.

This chapter discusses microencapsulation from four perspectives. First, it reviews some of the early technical developments, which helped to lay the foundation for the technology, as it exists today. Next, several commercial microencapsulation techniques (spray drying, air suspension coating, extrusion, spray cooling and spray chilling, centrifugal extrusion, rotational suspension separation, coacervation, and inclusion complexing) are discussed. The next section summarises important criteria, which should be considered for encapsulating food ingredients. The last section focuses on some of the commercially available encapsulating ingredient types.