Shrinkage modeling, drying kinetics and quality assessment of carrot cubes dried in a two stage spouted bed drying process

Abstract

A relatively easy to apply mathematical model based on the second Fick’s law inserting a correction factor α  to describe drying kinetics of unblanched carrot cubes in a two stage drying process considering shrinkage, using a semipilot spout bed dryer for the first stage and a lab scale spout fluidized bed dryer for the second stage was successfully developed. Drying of the carrot cubes was done at three drying temperatures 60, 70 and 80°C. It was possible to keep air velocity constant in each drying stage 1.65 m/s at the first stage and 0.68m/s and 1.35m/s in the annulus and spout respectively in the second stage. Effective moisture coefficients obtained 0.821 to 1.02 x 10-9 m2/s for the first drying stage and 0.262 to 0.481 x10-9 m2/s for the second drying stage were according to the published data for carrots in this kind of dryer considering shrinkage. The model fitted accurately the experimental drying with SEE of 0.122 to 0.210 when shrinkage was considered and α correction factor was inserted compared to SEE of 1.002 to 1.263 when shrinkage was neglected. Also residual analysis of models confirmed the adequacy of the model to predict drying kinetics.  Quality parameters obtained β-Carotene retention (80±5.4%), peroxidase residual activity (30-35%), pectin methyl esterase residual activity (83-95%) and rehydration ratio (4.5-5.3 water absorbed/kg dried solids) resulted similar to the ones reported in the literature and except for β-Carotene retention they all showed dependence with drying temperature.