Investigation of Hot Air-Assisted Radio Frequency as a Final-Stage Drying of Pre-dried Carrot Cubes

Carrot cubes were firstly blanched by radio frequency (RF) heating and then pre-dried by ultrasound-assisted osmotic dehydration (UOD). Hot air-assisted radio frequency (HA-RF) was applied as a final-stage drying method for pre-dried carrot cubes in this study. HA-RF drying characteristics and associated quality of carrot cubes were evaluated by comparing with those dried by conventional hot air (HA) and vacuum freeze (VF) drying. Moisture content of carrot cubes was reduced to < 10% (w.b.) after 235-260 min HA-RF drying with 6.0-7.0-cm electrode gap and 60 degrees C HA; the drying time was reduced by > 50% when compared with conventional HA drying (550 min). LF-NMR and MRI results showed that the inside moisture migrated to the outside along with the evaporation of surface moisture during the drying process which indicated that HA-RF was a relatively uniform drying process. Logarithmic model was found to be more suitable for HA-RF drying with R-2, RMSE, and SEM value at 0.994, 0.013, and 0.004, respectively. Carrot cubes dried by HA-RF had expected redness and relatively high hardness, and V-c retention rate was comparable with that dried by VF. This study demonstrated that HA-RF is an effective final-stage drying method for pre-dried carrot cubes.