MICROENCAPSULATION TECHNOLOGIES

16.2 MICROENCAPSULATION TECHNOLOGIES

Microencapsulation is the most common way to describe the processes used to prepare encapsulated food ingredients, because the particle size range varies from

1 to 2000 μm, depending on the technology applied to produce microcapsules. A wide variety of microencapsulation methods exist and, in addition, smaller, nanoscale particles can be produced using special technologies. Some selected encapsulation methods are listed in Table 16.1. The manufacturing technologies in the food area include spray drying, spray cooling or chilling, extrusion techniques, fluidized bed coating, coacervation, inclusion complexation, centrifugal coextrusion, and rota- tional suspension separation. 1

Spray drying is the oldest and most commonly used method in the food industry. The first encapsulated flavors were produced by spray drying in the 1930s, while

extrusion, the second most popular technique today, was not used in the flavor industry until the early 1960s. 4 The extrusion developed from the original method 5

involves mixing of the encapsulant into a molten carbohydrate, producing continuous filaments in which the encapsulant is entrapped within the shell matrix, similarly as

in spray-dried particles (see Figure 16.1). The difference is that spray drying is a dehydration process, while extrusion is a melting process. The encapsulation meth- ods that produce real coating membranes around the encapsulant are fluidized bed

Potential Use of Carbohydrates as Stabilizers and Delivery Vehicles

TABLE 16.1 Encapsulation Technologies and Size Range of the Product Particles or

the Particles That Can Be Coated 3

Size of the Final Particle or the Particle Encapsulation Method

That Can Be Coated ( μm)

Physical Methods

Centrifugal coextrusion 150–2000 Rotational suspension separation

30–2000 Pan coating

> 500 Fluidized bed

50–500 Spray drying

Chemical Methods

Simple/complex coacervation 1–500 Interfacial polymerization

1–500 Liposome entrapment

0.1–1 Nanoencapsulation

Oxygen dissolvation in the encapsulant

Oxygen Dissolvation A in shell matrix

B Oxygen diffusion across shell matrix C

FIGURE 16.1 Two single-core, one multicore, and one matrix (entrapped) microcapsule. In the case of the matrix microcapsule, the possible mechanism for the oxidation of the encap- sulant in a homogenous shell matrix is oxygen dissolvation from air (C) into the shell matrix (B), oxygen diffusion across the shell matrix, or oxygen dissolvation into the encapsulant droplet (A), which finally causes the oxidation reaction.

Functional Food Carbohydrates

coating, centrifugal coextrusion, coacervation, and rotational suspension separation. The principal difference between spray cooling/chilling and spray drying is the shell material; lipids are used in the former, while carbohydrates and proteins are applied in the latter, which naturally means a difference in the process temperature.

In cosmetic applications, microcapsules have been traditionally prepared by coacervation or by precipitation or polymerization methods. 6 Today, liposomes are also used for improvement of performance of active substances in cosmetics. The pioneer in the field of microencapsulation applications is the pharmaceutical indus- try. In contrast to the food industries, the shell materials used in drug formulations are often synthetic polymers, as is normally the case also in cosmetic applications. Synthetic materials offer much wider functionality than biomaterials, but are not usually approved in food applications and may often be rather expensive for mass- distributed food ingredients.

The most common types of microcapsules are schematically presented in Figure

16.1, together with a schematic description of the challenge of protection of the encapsulant from oxidation. A possible mechanism for the oxidation of the encap- sulant in a homogeneous single-phase shell matrix is also visualized in Figure 16.1. The three steps needed for oxidation are oxygen dissolution from air (C) into the shell matrix (B), oxygen diffusion across the shell matrix, and oxygen dissolution into the encapsulant droplet (A). When targeting both protection against oxidation and prevention of evaporation, control of very complicated transport mechanisms occurring in usually inhomogeneous matrices is required. Detailed research into these processes has only recently started to evolve. 7–9

The general targets for microencapsulation of food ingredients have been (1) better technological performance, such as better flavor survival during baking,

extruding, or deep frying, and (2) better storage stability. The possibilities to control the release of ingredients during processing with the aid of microencapsulation methods has also been of interest. The more recent developments concerning con- trolled release efforts are those dealing with targeted delivery of active agents related to human and animal health. The objective may be to prolong the duration of action of agents, to minimize unwanted reactions, or to maximize efficiency. 1

Encapsulation has been claimed to be today an art that is difficult for the food scientist to master due to lack of available information needed to make choices

concerning the most appropriate shell material and the most feasible encapsulation process. 10 The current progress in the food-related microencapsulation research is delivering new shell materials, such as β-cyclodextrins, into the market. A number of microencapsulated food ingredients exist in the market, but the volume is still relatively small compared with the huge potential that the various technologies offer. 3 The development of delivery vehicles for bioactive substances — whether focusing on improvement of overall storage stability or stability in processing or on more advanced desired release or targeted delivery systems — is inevitably a very chal- lenging area of research, if aiming at feasible technology based on nature’s own raw materials, such as carbohydrates.

Potential Use of Carbohydrates as Stabilizers and Delivery Vehicles