Yashashree Bhagat*, Meemansha Sharma**, Ayon Tarafdar***
Spray-drying is converting slurry or liquid feed into dried particulate form by atomizing the feed into a drying chamber where moisture is evaporated through hot air. The history of spray drying is traceable to a US patent issued in 1872 in the name of its inventor Samuel Percy. The first major application of spray technology was during World War II. During these times there was a major problem in the transportation of bulky milk with low shelf life. Subsequently, the dairy industry employed spray drying technology to produce milk powder for easy distribution. Since then, many advancements have been made to achieve high quality, free-flowing powdered products from a various materials. First nozzle atomizers were introduced, later followed with rotary atomizers. Spray technologies can produce powders with uniform particle size distribution and, is the preferred drying method in many industries such as foods and pharmaceuticals, especially for thermally-sensitive materials for instance, catalysts. If the feed is oxygen-sensitive (such as ethanol) then nitrogen is used instead of hot air.
Spray technologies have a set protocol under which they are operated. For instance, spray drying takes place in five steps: concentration (increase solid content), atomization (particle breakdown to increase surface area), droplet-air contact (counter current interaction of atomized liquid with hot air), and droplet drying (>95% moisture evaporated) and separation (Cyclones, bag filters, and electrostatic precipitators are used). The particles descend to the bottom of the chamber for primary separation, and a small portion of the particles remain trapped with the air and must be retrieved in separation equipment such as cyclone. A carrier material (such as maltodextrin, gum arabic, alginates, carrageenan, waxes, protein isolates, and cellulose derivative) is usually supplied during drying to protect heat sensitive elements.
Spray technology is an essential part of food and beverage manufacturing operations. It is used for everything from cleaning tanks to glazing cakes, and from sanitizing bottles to portioning vitamins. The experience in food processes and the wide range of products for the sector give us the opportunity to improve the quality of the plants, increase operational efficiency and reduce waste. Within the meat processing industry, spray technology applications include carcass washing, screen cleaning, boot cleaning, spray chilling, and sanitizing evisceration tables, while dairy processors use spray technology for apportioning preservatives to cheeses and powder formation. Beverage processors use spray technology to sanitize bottles, clean tanks with caustic solutions and so forth. Further spray technology has been found to be effective in encapsulation. Encapsulation is a process to embed core active agents within a carrier material to improve delivery of bioactive molecules enhancing their stability while decreasing their sensitivity. This technology is widely used for nutraceutical compounds with low stability and heat sensitive substances.
The particles produced range from a few nm to a few millimeters. Encapsulation technology is now well developed and accepted within the pharmaceutical, chemical, cosmetic, foods and printing industries. In food products, fats and oils, aroma compounds and oleoresins, vitamins, minerals, colorants, and enzymes have been encapsulated. Spray chilling is another important application which is used to produce lipid-coated active materials. The core substance could be lipid-soluble, dry particles, or aqueous emulsions. Spray-chilling involves a setup similar to fluidized bed spray granulation, keeping the particles at a low temperature, but the key difference being the melting point of lipids. Unlike spray-drying, there occurs no evaporation in spray chilling. Spray chilling has a temperature range of 34–42°C, whereas it is higher for spray cooling. Spray freeze-drying (SFD) is another method which combines the spray drying and freeze drying and has found major application in probiotic encapsulation and drying volatile compounds to retain their functional properties due to low temperature processing. It is applied in packaging, to spray antimicrobials into vacuum packages before sealing. The antimicrobials are evenly distributed around the product when vacuum-sealed, effectively sterilizing it.
Spray technologies are very economical, scalable and have lower operational costs. The major challenge facing the spray industry today is the development of more efficient nozzles. The use of ultrasonic nozzles is constrained to some applications such as microencapsulation. Ultrasound in spray drying is still not in practice to its full potential majorly due to lack of suitable large-scale reactor, low throughput values and cost of operation of ultrasound. Use of ultrasound in spray drying has been found to be much effective in microencapsulation, drying probiotics to maintain the cell viability, improving the texture of food products, and reducing the microbial contamination as well. There are several areas where the use of ultrasound in spray drying needs to be amended to meet the desired objective.
Kumar, D., Mishra, A., Tarafdar, A., Kumar, Y., Verma, K., Aluko, R., Trajkovska, B., & Badgujar, P. C. (2021). In vitro bioaccessibility and characterisation of spent hen meat hydrolysate powder prepared by spray and freeze-drying techniques. Process Biochemistry, 105, 128-136.
*National Institute of Food Technology Entrepreneurship and Management, Sonipat, Haryana 131 028, India
**Division of Pharmacology and Toxicology, ICAR-Indian Veterinary Research Institute, Izatnagar, Bareilly 243 122, Uttar Pradesh, India
***Livestock Production and Management Section, ICAR-Indian Veterinary Research Institute, Izatnagar, Bareilly 243 122, Uttar Pradesh, India