Modification of powders’ properties, such as flowability, wettability, flavour, colour, etc., is very important for many applications. Even more and more biologically active substances are used in various industries because of their beneficial functional properties and effects on the environment and human health.
The coating process of materials can be employed to enhance, time or tune the effect of functional ingredients and additives, or for extended drug release applications.
The process consists of two steps: sprayed coating solution, through a nozzle, on the particles; evaporate the solvent, in order to obtain a coating layer onto particles surface.
During the traditional coating process based on organic solvent, the solvent needs to be recovered due to environmental pollution. Coating processes with aqueous dispersions are time and energy consuming caused by the low concentration of coating polymer and large amounts of water which need to be evaporated.
Dry coating is not really a new technology. It had been applied in chemical, aeronautical, metallic, wood and paper industries mostly for coating or recovering woods, metals or any desired surface by paints, varnishes, different polymers or precious metal to protect them against corrosion or to reinforce them. Its application to food area is quite recent and is still in its infancy.
Dry particle coating, consists in coating relatively large particle size (core material or host) with fine particles (guest). The adhesion of these particles is made using mechano-chemical treatment or using plasticizer. The using of plasticizer is particularly indicated to coat particles that are relatively soft and very sensitive to heat and can be deformed by severe mechanical forces.
Compared to solvent and water based coating the dry coating method is favourable regarding environmental friendliness, safety and cost. It might be a very suitable coating method in order to coat foods and drugs which are sensitive to organic solvents or water.