Effects of high-intensity ultrasound on drying kinetics and antioxidant properties of passion fruit peel

• High temperatures and US application increased drying rate of passion fruit peel.
• US reduced both internal and external mass transfer resistance.
• US influence was higher at the mildest temperatures tested (40 and 50 °C).
• Drying conditions affected the antioxidant potential of dried passion fruit peel.
• The better antioxidant potential was obtained in samples dried at 40 °C with US.

The aim of this study was to evaluate the effect of temperature and ultrasound application on drying kinetics and antioxidant potential of passion fruit peel. To this end, drying experiments (1 ms−1) were carried out at 40, 50, 60 and 70 °C without and with ultrasound application (21,7 kHz, 30.8 kW/m3). Two diffusion models based on Fick's second law were used to mathematically describe the drying kinetics considering or not the external moisture transport resistance. The antioxidant capacity and the total phenolic content of dried passion fruit peels were assessed. The increase in temperature and the application of ultrasound significantly reduced the drying time. Modeling showed that the application of ultrasound increased both the effective diffusivity and the mass transfer coefficient, particularly at the mildest temperatures tested, 40 and 50 °C. Under these conditions, ultrasound application also reduced the loss of total phenolic content and maintained the antioxidant activity of dried passion fruit peel.