Encapsulation of water sensitive products: effectiveness and assessment of fluid bed dry coating

Today, there is a real interest in the use of products containing some living cells or some other fragile substances in many industries, agriculture, chemical, pharmaceutical and food, because of their beneficial functional properties and effects on the environment and human health. These products are used or processed as dried substances to enhance their stability, viability and activity and they are generally encapsulated or attached to a support (tablet or coated particles) for these purposes. The problem is that with all traditional aqueous coating processes, these products can come in contact with water and can loose all their beneficial characteristics. A new method for encapsulating such material, which consists in coating directly the core material with a fine dry powder, is described here. A comparison with the classical aqueous coating system will show various advantages such as high coating yield and energy saving in addition to the non-wetting of the product. The resulting dried coated particles are very permeable and can be dissolved rapidly in water. The results also show some disadvantages such as the high hygroscopicity and the low strength of the coating film. These disadvantages, along with the water uptake during the process (2%) indicate that this dry coating system, which presents some real potential for industrial application, needs some improvements, especially the suppression or the reduction of water in the fluidising and atomizing air.