The three stages that occurs in a spray dryer before drying is accomplished includes:
*Atomization
*Spray air mixing and moisture evaporation
*Dry product separation from the exit air
The process of spray drying consists of the transformation of a product in fluid form to the solid state in the form of powder. The spray-drying process reduces water activity of products, retards bacterial degradation and extends the product’s shelf life. All spray dryers employ atomizer or spray nozzle to disperse the liquid or slurry into a controlled drop size spray.
The process is done through the dispersion of droplets from the product inside a chamber, in contact with hot air. When the droplets and the heated gas come into contact, the solvent in the droplets evaporate, leaving a dry powdered product.
In this process, substances known as carriers or encapsulating agents can be added. Starch, modified starch, maltodextrin, solid corn syrup and gum Arabic etc., are kinds of high molecular weight carbohydrates commonly used as spray-drying carriers. The main functions of spray-drying carriers are to increase glass transition temperature of product, and reduce stickiness and wall deposition during spray-drying.
Spray drying results from application of energy, which acts on the liquid to the point of causing its rupture and disintegration, in order to divide it into millions of individual particles, thereby creating a mist or spray of droplets.
The development of spray drying equipment and techniques started in the 1870s. Spray drying has come of age ever since the technique was used during the World War II, because the idea to reduce the transport weight of foods and other materials became important.
Recently, the spray drying technique has been applied extensively for the production of functional foods, pharmaceuticals and nutraceuticals. Encapsulation using spray drying is highly preferred due to economic advantages compared to other encapsulation methods.
Food powder production by spray drying
