Drying process and quality characteristics of contact ultrasound reinforced heat pump drying on kiwifruit slices

Abstract

Contact ultrasound reinforced heat pump drying (CUHPD) experiments of kiwifruit slices were performed to investigate the effect of ultrasound application on drying process, microstructure, and several nutrient components of kiwifruit slices. The results showed that the CUHPD of kiwifruit slices was an internal diffusion-controlled process, in which ultrasound application could improve the dehydration rate significantly, and higher ultrasonic power led to shorter drying time. Scanning electric microscopy results illustrated that the ultrasound treatment could produce more micropores and larger microchannels inside kiwifruit slices, and thus reduce the hardness and brittleness values. Both ultrasonic power and drying temperature could significantly affect the total phenolic content, VC content, and total sugar content. Contact ultrasound application in the heat pump drying (HPD) process was conducive to improve the nutrient contents at all drying temperatures. Hence, contact ultrasound application is a promising way to effectively promote the dehydration rate and to improve the product quality of HPD on kiwifruit slices. Practical applications Heat pump drying (HPD) is one of the modern drying methods and has some excellent advantages such as energy-saving and easy operation. However, it has a certain disadvantage like long drying time for those agricultural materials with great internal mass transfer resistance. In this study, the contact ultrasound reinforcing technology was applied to accelerate internal water transfer and improve the drying rate of HPD on kiwifruits. The results showed that the contact ultrasound application could produce a significant reinforcing effect on internal moisture diffusion and dehydration rate, and then reduce the drying time. The increase in ultrasonic power was conducive to improve dried kiwifruit's quality and protect nutrient components in kiwifruit slices compared with single HPD. Therefore, CUHPD is a promising drying method for kiwifruits and can even be effectively applied for other agricultural product drying.