Modeling for thin layer drying of black pepper (Piper nigrum) in a reverse air flow dryer

Abstract

Drying of freshly harvested green pepper (Piper nigrum) was performed in a reverse air flow mechanical dryer (RRLT-NC – 101). Fresh and blanched pepper of varieties, Sreekara and Panniyur-1 were dried at 50°C, 55°C, and 60°C. Blanching was done by dipping in boiling water for 1 min. The experimental data for moisture loss was converted to moisture ratios and fitted to five thin layer drying models to describe the drying process mathematically. The results were compared for their goodness of fit in terms of coefficient of determination (r2), root mean square error (RMSE) and mean square of deviation (χ2). Logarithmic model was found most suitable to describe the drying process of black pepper. The unblanched Sreekara took 42, 34, and 26 h and blanched took 36, 30, and 24 h to dry from moisture content of 180.89–9.4% d.b. at air temperatures of 50°C, 55°C, and 60°C, respectively. In case of Panniyur the unblanched took 44, 36, and 28 h and blanched took 37, 32, and 26 h to dry from moisture content of 197.62–9.2% d.b. for the same temperatures. The effective moisture diffusivity varied from 3.28 × 10−7 to 6.44 × 10−7 m2/s. The activation energy was higher for unblanched than for blanched black pepper varied between 39.45 and 44.05 kJ/mol.