Powder production by Spray Drying
Drying Several drying techniques (spray drying, vacuum drying, freeze drying and spouted bed drying) have been proposed for the production of powder dry extracts. Amnog them spray drying has been widely utilized for the preparation of herbal powders due to the high stability of powders or granules obtained from liquid feed in a single step (Senna et al., 1997 and Oliviera et al., 2000). By decreasing water content and water activity, spray-drying is generally used in food industry to ensure a microbiological stability of products, avoid the risk of chemical and/or biological degradations, reduce the storage and transport costs, and finally obtain a product with specific properties like instantaneous solubility for example (Gharsallaoui et al., 2007). Spray drying consists of atomization of feed, spray-air contact, drying, and separation of the dried product from the drying air (Deis, 1997). Atomization of liquid feed provides formation of droplets which pass through hot-air stream. The drying process of such droplets is very rapid with intensive moisture evaporation at the surface of the droplets, which keeps the droplets cool until the dry state is reached (Masters, 1991). The drying process can be completed within a short period of time, thus enabling to prepare powder without heat degradation even at comparatively high air temperatures (Mani et al., 2002).
For the improvement of spray drying process efficiency, and for the improvement of produced powder properties, various excipients (drying additives) were used. Addition of drying additives affects: efficiency and cost of drying process, physical properties of liquid feed, physical properties of produced powder, and chemical properties of powders, shelf life and stability, as well as sensory characteristics of obtained products. Therefore, the selection of adequate excipients and adequate quantity of excipients is necessary. Most commonly used excipients in spray drying of herbal products are high molecular weight carbohydrates, such as starch, modified starch, dextran, maltodextrins (MD), solid corn syrups, gum arabicum, cyclodextrins, etc. (Oliviera et al., 2000). Currently, MD has been most frequently used as excipients.