Ultrasound-assisted drying of apples – process kinetics, energy consumption, and product quality

Convective drying is a method of preserving fruit. Due to the low energy efficiency of the dryers, it is also one of the most energy intensive. For this reason, modern drying techniques are being sought. They are required to be energy efficient, sustainable and produce high quality products. The aim of this work was to determine the effect of ultrasound on the kinetics and energy consumption of convective drying of apples and the quality of the products. The convective drying process and two US-convective processes with different ultrasonic power were tested. Three apple varieties were dried. Drying kinetics, energy consumption, and product quality (water activity and color change) were compared for the tested processes. Drying kinetics was mathematically modeled. The use of ultrasound accelerated the process in each case. The drying time was reduced and the speed of the process increased. This increase was mainly due to the vibration effect, which caused an increase in the mass transfer coefficient. The use of ultrasound resulted in a decrease in the water activity of the product and a decrease in the color change of the dried material compared to that obtained by the convection method.