Abstract
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 °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 R2, 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 Vc 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.
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Funding
This research was conducted in the Department of Food Science and Technology, Shanghai Jiao Tong University, Shanghai, China, and financially supported by Shanghai Jiao Tong University “Agri-X” Fund (Agri-X2016006) and Science and Technology Commission of Shanghai Municipality (19DZ2284200).
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Highlights
•HA-RF was applied as a final-stage drying method for pre-dried carrot cubes.
•HA-RF reduced drying time by > 50% when compared with HA drying (550 min).
•Logarithmic model can be used to well describe HA-RF drying process (R2 = 0.994).
•HA-RF-dried samples had relatively good color, texture, and Vc retention rate.
•HA-RF was a promising final-stage drying method for pre-dried carrot cubes.
Industrial Relevance
This study proposed and investigated hot air–assisted radio frequency (HA-RF) heating as a final-stage drying method for carrots cubes. Drying is an energy-extensive process, especially for the falling rate drying period. HA-RF takes advantage of fast and volumetric heating characteristics of RF heating; thus, it can significantly shorten the drying time and maintain sample quality very well at the same time. Therefore, it holds great potential as an industrial final-stage drying method for fruits and vegetables.
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Gong, C., Liao, M., Zhang, H. et al. Investigation of Hot Air–Assisted Radio Frequency as a Final-Stage Drying of Pre-dried Carrot Cubes. Food Bioprocess Technol 13, 419–429 (2020). https://doi.org/10.1007/s11947-019-02400-0
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DOI: https://doi.org/10.1007/s11947-019-02400-0