Ultrasonic-Assisted Convective Drying of Apple Slices

Abstract

A promising approach for the application of ultrasound to assist in convective food drying was developed and tested in this study. The application of ultrasound is based on the transmission of ultrasonic energy as a combination of airborne contacts and through a series of solid contacts between the ultrasound element and the product tray as the ultrasonic vibration transmitting surface. A computer-based ultrasonic drying setup was built to allow continuous recording of the process variables in real time and enabled simulation of dehydration to be accomplished under controlled conditions over a range of drying parameters. Apple slices were dried using the drying setup to study the influence of ultrasound in combination with conventional hot air drying on drying kinetics and product quality.

The results from this work indicate that ultrasound can simultaneously be applied to accelerate the processing time (i.e., reduce energy consumption and increase production throughput) in conventional hot air drying without compromising product quality. It appears that the magnitude of influence of ultrasound to enhance the air-drying process depends on the process variables employed. In particular, the ability of ultrasound to improve the efficiency of the convective drying process appears to be maximized when using low temperature and high ultrasonic power level. This finding maybe very useful when there is a need to effectively dehydrate heat-sensitive products or when shorter drying times are required in order to achieve better retention of the functional and nutritional properties of the product.

Keywords:

• Apple
• Dehydration
• Drying
• Drying kinetics
• Microstructure
• Ultrasonic-assisted drying
• Ultrasound

ACKNOWLEDGMENTS

The authors thank Dr. Seong Kang (formerly with CSIRO Food and Nutritional Sciences) for his assistance in carrying out the laboratory experiments, Vicki Eggleston for undertaking the texture analysis, and Dr. Manoj Rout and Katherine Zerdin (formerly with CSIRO Food and Nutritional Sciences) for the CLSM analysis. The authors also thank Dr. Raymond Mawson and Dr. Roman Buckow for reviewing the article and Dr. Lyndon Kurth for his helpful comments.