Combined Effect of Airborne Ultrasound and Temperature On the Drying Kinetics and Quality Properties of Kiwifruit (Actinidia Deliciosa)

Abstract

Drying is one of the most used options for the stabilization of the surpluses resulting from kiwifruit industrialization for their upcycling. However, drying conditions, such as drying temperature or ultrasound application during drying to intensify the process, can highly affect its final quality. Thus, with the aim to assess the combined influence of temperature and ultrasound application in the drying process of kiwifruit, ultrasonically assisted drying experiments were performed at 40, 50, 60 and 70 ºC. The process kinetics was greatly dependent on the temperature, as shown by the activation energy value obtained, 30.95 kJ/mol. Ultrasound application increased the drying kinetics, with its influence being more marked at the lowest temperatures tested. The increase in effective diffusivity and the mass transfer coefficient induced by ultrasound application was similar to the increase induced by an increase of drying temperature of 10 ºC. Drying caused a significant change in the color although the use of ultrasound helped to preserve it at the higher temperatures. Antioxidant capacity and vitamin C content decreased after drying, but the total phenolic content increased. The greatest retention of the antioxidant properties was observed in ultrasonically assisted samples dried at the highest temperatures. In the case of fiber properties, the best results were obtained at intermediate ones. Drying kiwifruit at 60 ºC with ultrasound application could serve as a means of balancing a fast drying process and good final quality.