Abstract
The effects of drying temperature (120 °C to 200 °C) on drying characteristics of black tea leaves using superheated steam dryer (SHS) were investigated. It was observed that increased drying temperature caused higher drying rate that helped to shorten drying times. The effective diffusivities of moisture transfer in SHS ranged between 2.30 × 10–10 and 3.90 × 10–10 m2/s within the temperature range tested. The effective diffusivities were correlated by Arrhenius relationship with Arrhenius constant and activation energy estimated at 1.07 × 10–8 m2/s and activation energy 12.34 kJ/mol, respectively. Increased in drying temperature and time significantly decreased the brightness (*L) of tea leaves from 26.34 to 22.66 and TPC from 87.93 to 42.39 mg/g. However, comparison to commercial black tea showed that SHS dried-tea leaves exhibited better colour attribute and 91.4% higher in phenolic content.
Nomenclature
- A
Area of drying (m2)
- Deff
Effective diffusivity (m2/s)
- Do
Diffusivity at an infinite temperature (m2/s)
- Ea
Activation energy for moisture diffusion (kJ/mol)
- L
Thickness of tea leaves (m)
- Mo
Initial moisture content (g, dry solid)
- Me
Equilibrium moisture content (g, dry solid)
- MR
Moisture ratio
- Ms
Mass of the bone dry solid (g)
- N
Drying rate (g/m2)
- R
Gas law constant (J/molK)
- R2
Coefficient of determination
- RMSE
Root mean square error
- SSE
Sum square error
- T
Drying temperature (°C)
- T
Drying time (mins)
- Wi
Initial weight (g)
- Wf
Final weight (g)
- X
Moisture content (gH2O/g, dry basis)
- X2
Chi-square
Acknowledgements
Authors would like to acknowledge Short Term Grant Universiti Sains Malaysia (304/PTEKIND/6313331) for funding this project, Ministry of Education of Malaysia and Universiti Malaysia Perlis for their scholarship under Bumiputera Academic Training Scheme (SLAB/SLAI).
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