Modelling of thin-layer drying kinetics of red chillies Original Research Article

Drying kinetics of red chillies in a thin-layer dryer was investigated within a temperature range of 50–65 °C. The time required to dry chillies from an initial moisture content of around 325% (d.b.) to the final moisture content of around 10.5% (d.b.) was 26, 20, 16 and 13 h at 50, 55, 60 and 65 °C of drying air temperature respectively. The average capsaicin content and the value for red/green chromaticity coordinate colour (a*) of dried chillies decreased from 0.60% to 0.34% and 25.77 to 14.73, respectively, as the drying air temperature increased from 50 to 65 °C. The overall performance of the chillies dried at 55 °C was the best, when the quality attributes viz., drying time, capsaicin content and red colour were considered. Drying curves obtained from the experimental data were fitted to different drying models and found that the Page and Kaleemullah models are suitable to predict the moisture ratio of chillies at different drying air temperatures of a thin-layer dryer. The effective moisture diffusivity (Deff) of chillies increased from 3.78 × 10−9 to 7.10 × 10−9 m2/s as the drying air temperature of a thin-layer dryer increased from 50 to 65 °C. The activation energy of diffusion (Ea) was calculated as 37.76 kJ/mol.