Microencapsulation of essential oils A matter of gas flow management

Author / Editor: Dipl.-Ing. Arne Teiwes* / M.A. Manja Wühr

Essential oils contain the power of nature. To use this power companies aspire to modern process technology. Because the Microencapsulation in closed cycle mode ensure high-quality products as well as efficient production process.

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Microencapsulation of essential oils by spray granulation using spouted bed technology
Microencapsulation of essential oils by spray granulation using spouted bed technology
(Picture: Glatt Ingenieurtechnik; © silencefoto; © mnimage - Fotolia)

Essential oils are volatile substances that are susceptible to oxidation and light. They change or can even lose their properties when coming into direct contact with the environment. Up to now, these phytochemicals have found numerous uses and applications. In the field of food and feed technology and in the cosmetics industry, these odor-intensive and flavorful substances are used, amongst others, for improving the sensory or functional properties of products. Moreover, due to their various pharmacological effects, the pharmaceutical industry makes multifunctional use of the natural substances. For protection and easier handling, as well as for better dosing and targeted release properties, these substances are increasingly offered and used by various industries in an encapsulated and often free-flowing form.

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Several chemical and physical processes are available for encapsulation. One key physical method is the microencapsulation by spray granulation in a spouted bed process. Using a matrix containing oil-in-water emulsion as a starting material, the spray granulation yields solid particles of defined size in which the oil has been very finely distributed in an optimal way. The inclusion of a liquid within a solid matrix inevitably increases the moisture of the particles and with that their tendency to agglomerate. This makes a trouble-free application of traditional fluidized bed processes difficult.

Continuous Spouted Bed Technology

These encapsulation problems can be avoided with the continuous spouted bed technology developed by Glatt Ingenieurtechnik. Furthermore, due to the thermodynamic equilibrium conditions present in a spray granulation process, a certain part of the oil to be encapsulated escapes from the granulation zone along with the fluidizing air. This has two drawbacks; firstly, a considerable part of the active substances is lost in the production process and secondly, the permissible legal limits for volatile organic substances in industrial exhaust gases will be exceeded.

Usually, oil-containing granules are produced in a commonly used single-pass system. For different volatile oils, the processing parameters with the highest impact were determined by sensitivity analysis for those systems. Adjustments of the formulation, rate of spraying and layer temperature resulted in optimal encapsulation conditions for this mode of operation and yielded a maximum possible oil recovery rate in the granules. Nevertheless, depending on the material system used, up to 20 % of the active substances will still be lost in such a system.

Consequently, a higher oil recovery rate of the granules can only be achieved with a different processing gas flow management. Performing the encapsulation in a closed cycle mode offers the possibility of reducing the decisive partial density ratio of particle to gas. The recirculation of the exhaust air allows selective adjustment of the oil concentration in the supply air. The resulting increase of the partial pressure of the oil in the supply air has an immediate effect on the transport of liquid in the granules during the encapsulation process. Thus, the reduced partial pressure gradient of the oil between the particle and the ambient gas leads to reduced oil loss in the granulation process.

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