Evaluation of quality parameters of dried carrot cubes in a spout-fluidized-bed dryer with and without draft tube

Unblanched Carrot cubes (0.9 × 0.9 cm) were dehydrated in a spout-fluidized-bed dryer with and without draft tube. The temperatures used for drying in the annular region were (60, 70 and 80 °C) and they were combined with the same temperatures in the spout. No constant period was observed in the drying curve during the drying process, so a polynomial degree 5 or 6 was used to fit the experimental data in order to estimate the effective diffusion coefficients. The effective diffusion coefficients calculated are similar to the ones reported in the literature (0.66 to 1.60 × 10 to 9 m²/s) for carrots dried in spout-fluidized-bed dryers. As quality parameters, the β carotene content was estimated and it was found that practically no degradation occurred in any drying experience. Also the peroxidase (POD) residual activity and the pectin methyl esterase (PME) residual activity were estimated and the POD residual activity resulted between (40 and 60 %) and PME in the range of (70–100 %) depending on the drying temperatures. Rehydration ratio also resulted similar to the values reported in the literature 5.2–6.3 with respect to the dehydrated mass. A loss of around 33–40 % of soluble solids was found by leaching process during rehydration experiences. No difference in the quality of dried product was observed with or without the use of the draft tube however the required air per kilogram of dried solid was 7.8 % lower when the draft tube was used making the drying process 7.8 % more economic.