Food drying enhancement by ultrasound – A review

• Review of the ultrasonically-assisted drying was done with respect to processes type and apparatus used.
• Positive effect of ultrasound on the drying kinetics, quality of obtained products and energy consumption was found.
• Lack of effective generators of power ultrasound was distinguished as the primary constraint ahead industrial application.
• The necessity for detailed studies on ultrasound application in drying is emphasized.

BackgroundDrying is one of the most popular methods of preserving a wide variety of food and agricultural products. Unfortunately, this unit operation may negatively influence product quality. Moreover, due to the high heat capacity of water, drying is usually a long-lasting and energy-intensive process, thus new drying techniques are continuously being sought.Scope and approachThis review presents the current state of art in ultrasonic-assisted drying. Despite immense knowledge on the principles of ultrasound generation and action, this technology has found no practical application in industrial drying yet. In this paper we tried to find the reasons for this state of affairs. Up-to-date designs of dryers using ultrasound to enhance the drying process and the various possible mechanisms of accelerating the drying process with the application of ultrasonic waves are discussed. The influence of ultrasound on the product's quality (dried food) is judged and described.Key findings and conclusionsThe analysis of the results presented by the researchers here allows to state that applying ultrasound to drying caused a shortening of the drying time and could reduce total energy consumption. Moreover, due to the small “temperature effect”, the quality of the obtained products was noticeably better as compared to the control processes (without ultrasound enhancement). The lack of an effective technology for generating power ultrasound in air was distinguished as the primary constraint for industrial application of this technology. The necessity of conducting detailed studies on ultrasound application in drying was emphasized.