Food is perishable in nature so the preservation of food is needed to prevent its damage or decay or spoilage under normal environmental conditions. The main aim of food preservation is to prevent or delay the growth of microorganisms such as bacteria, yeast and moulds as well as it prevents the oxidation of fats. Preservation maintains the quality and nutritive value of food as well as extends their shelf-life too. However, there is a preservation method that changes the phase of liquid food in powder form, i.e. spray drying.
Spray drying is the process where a mixture of compounds is made in its liquid or slurry form that is finally converted into dry powder form. This drying technique emerged way back in 1860s and was used during World War II. It helped to make easy shipment of larger quantities of food within limited storage area. In this spray drying process, the moisture is removed from the liquid slurry through a hot gas. As per the food safety aspect, this is the best preservation method.
Brief of spray-drying process:
The process proceeds with the spraying of liquid in the form of mist inside the spray dryer. These droplets are readily evaporated and get converted into solid particles. When the liquid gets sprayed through the atomizer or nozzle, heated gas of the chamber quickly binds with it in high surface-to-mass droplets within the drying chamber. It results in the evaporation of the solvent from the liquid. The solid particles or the dry powder is collected from the bottom of the drying chamber. Mostly rotary atomizers are used in spray dryers to avoid the problem of blocking due to any minute coarse particle. Air is used as the heating medium; but in some cases nitrogen may be used (if the liquid contains flammable solvent). The flow of air remains in co-current direction for the easy and efficient drying process.
These spray dried powders have an excellent agglomeration or reconstitution property. It means that these powders would dissolve easily in solvent for the consumption purpose. The process gets completed within 3 to 30seconds. The size of particles ranges between 2 to 500mm. The safety of the product’s quality and nutritive values remains maintained.
One of the best examples for preservation by spray drying is milk. Milk is a perishable food product, i.e. it is prone to quick spoilage if it is not stored within proper temperature conditions. Milk gets spoiled within 24 hrs in summer. Therefore, to extend the shelf-life of milk; spray drying is being used now days on a huge scale. Milk contains 80-90% water, thus spay drying reduces its bulk weight and increases its shelf-life, for example; powdered milk can be kept for six months without any sign of spoilage. The nutritional content of powdered milk remains well maintained. Skim milk is produced largely worldwide by spray drying process. Moreover, the transportation costs get reduced. In case of food scarcity or any emergency spray dried instantinized milk powder can prove to be the best survival medium.
List of food products that can be spray dried:
- Egg products
- Fruit juices
- Starch and derivatives
- Tea and coffee
- Cereals and spices
- Flavors and colors
- Plant extracts
- Fat Soluble Vitamins
- It is a complete and continuous process.
- Drying is done very quickly and rapidly.
- Cost effective
- Uniform and controlled sized particles are formed (also makes easy the tabletting process).
- The heat and mass transfer ratio is larger for particles; thereby it provides excellent solubility of the product.
- Spray drying is better as compared to other methods of drying such as, ovens, freeze dryers, etc. The other methods produce irregular shaped and sized particles with low solubility index.
- Reconstitution makes the spray dried product look as fresh as the fresh one.
- Spray dried products can be easily packaged and transported.