Effect of ultrasound-assisted drying on drying kinetics, color, total phenols content and antioxidant activity of pomegranate peel
A. Niveditha, D. V. Chidanand, C. K. Sunil
Abstract
The study investigated the effect of ultrasound (US) pre-treatment on drying kinetics, color, total phenols content and antioxidant activity of pomegranate peel (PP). The US pre-treatment was carried out at a frequency of 24 kHz at room temperature for two time periods of 5 and 10 min. The pretreated PP were then dried in a convective tray dryer at two different temperatures (70 and 80°C). The US pre-treatment had a significant influence on reducing the drying time (approx. 45% reduction) of PP. Five thin-layer drying models were fit to study the drying kinetics in which Midilli's model gave the best-fit curve. The effective moisture diffusivity (Deff) of PP ranged from 5.44×10−09 to 1.49×10−08 m2/s. The PP activation energy (Ea) decreased with increased exposure time. The color values (ΔΕ*) increased with increasing treatment time and temperature, however, no significant difference among color values was observed. The total phenol content and antioxidant activity were higher in US-treated peel powder than in untreated (UT) PP. The US pre-treatment of 10 min and dried at 70℃ successfully reduced degradation of total phenolic content and antioxidants and is recommended for PP drying pretreated with US