The production of dried flavourings is mainly based on the technique known since many years: the microincapsulation by spray dry. Shortly that method can be described as follows (Di Giacomo and Mincione, 1994):
• formation of an emulsion or dispersion, enough stable and with small particles, formed between the essential oil and the material the forms the external coating of the microcapsules;
• successive spraying for the formation of the microencapsulated material.
Among the materials commonly used are different starch types, gums, organic polymers, and introduced more recently, also some modified gels. The choice of these materials is limited by the instrumentation available to spray and by the specifications necessary for the good dispersion, the viscosity and a commercially profitable concentration. Moreover, if the product is used in the food industry, the encapsulating material must be accepted as food additive.
Usually the amount of dry material in the emulsion can vary between 25 and 50 per cent. The dispersion can be obtained above or below room temperature depending on the essential oil character and on the material used for the dispersion: the product obtained is usually water soluble. The water resistant capsules can be obtained by using some modified starches.
The spray drying procedure is usually performed by atomisarion of the dispersion, or of the emulsion, in a large drying chamber; initially is formed a fine dust made of essential oil particles contained in a film of the solvated coating material. The solvent is rapidly eliminated from the liquid film, leaving the solid dry coating of the capsule that contains the essential oil.
In the plant the emulsion is transferred to the spray chamber by a pump, and successively to the dryer chamber. The air used during the process, pre-filtered and pre-heated, is introduced by a flow regulator in the same chamber (temperature 200-280 °C), and mixed with the fluid drops.
The time of permanence in the chamber can be adjusted depending on the system of ventilation.
Most of the water evaporates almost instantaneously. The humid air is introduced in a twister (90-120 °C) where a further amount of powder is carried and recovered by a venting system.
The dry powder is collected on the bottom of the main chamber, cooled with cold air and added with the recycled powder, then sent to the last twister.
The final product is sieved and stocked in containers. The amount of water in the powder is between 3—5 per cent. The size of the particles can vary between 5—2000 pm, but generally ranges from 5—400 pm.
The encapsulation can also be obtained by cryo-drying.
Numerous are the proposed applications for the microencapsulated products in the food and flavour industries. The most important could be the essential oil microencapsulation for bakery products. The micro-encapsulation of essential oils with a coating the is resistant to the high temperatures of the oven during the initial stage of cooking, allows the reduction of the amount of aroma used, without loss of the flavour.
The advantages offered by using encapsulated products as flavours are summarised below:
• the strength and the quality of the aroma are totally protected against evaporation, oxidation and can be maintained at high temperatures and for periods of time higher than 12 months;
• the microencapsulated product can be completely introduced in powder mixtures by using simple mixing procedures, obtaining a fine and uniform dispersion;
• the powders, that are bacteria free, usually present excellent hygienic properties. They contain a reduced amount of water, and can be easily mixed to different dry food products.
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