Ultrasound as pretreatment for drying garlic slices in microwave and convective dryer

• DOI: 10.1007/s10068-018-0483-1
• Publication Date: 2018-10-04T07:34:51Z
• Authors: Hamza Bozkir; Ahsen Rayman Ergün; Yeliz Tekgül; Taner Baysal
• Keywords: Tray; Microwave oven

The effects of ultrasound pretreatment (US) before hot air drying (HAD) and microwave drying (MWD) of garlic slices were investigated. For this aim ultrasonic bath at 30 °C for 30 min (35 kHz), microwave oven at 540 W power and tray dryer at 60 °C and with 1.0 m/s air flow rate were used to reach the final moisture content of 5%. Drying rate increased in the US + HAD and the US + MWD groups by 19.30% and 13.82% respectively in comparison with control groups. The effective moisture diffusivity (Deff) of garlic slices were calculated from Fick's diffusion model for the HAD, US + HAD, MWD and the US + MWD groups as 1.420 × 10-10, 1.826 × 10-10, 1.177 × 10-8, 1.363 × 10-8 m2/s respectively. The rehydration rates increased, and bulk densities were decreased in the US + HAD and the US + MWD compared to the control groups. The color values were significantly affected after ultrasound pretreatment. Redness, and yellowness increased most in the US + HAD group.