Air drying of blueberry fruits: Drying kinetics, mathematical modeling and physical properties

Abstract

The hot air convective drying of blueberries (Vaccinium corymbosum) in a thin layer was performed using a laboratory-scale dryer. The experiments were carried out at drying air temperatures of 60, 70 and 80 o C, and drying air velocities of 0.5 and 1.5 m/s. At higher values of the drying air temperature and the drying air velocity, less time was required for the convective drying of blueberries, i.e. the drying time of blueberries decreased with increasing drying air temperatures and velocities. The experimental data obtained during the drying process were fitted to ten different mathematical models. The Midilli et al. model was found to be the most appropriate model for explaining the drying behavior of blueberries during convective drying. Effective moisture diffusion coefficients were calculated using the Fick's diffusion model, ranging from 9.66 x 10-12 m2 /s to 9.67 x 10-11 m2 /s. These values were found to increase proportionally with the increase in drying air temperatures and velocities. The lowest total color change and shrinkage of dried blueberries were recorded during freeze drying. A water activity less than 0.6 was measured at a blueberry moisture content of 0.235 kgw/kgd.m, a drying air temperature of 26 o C and a relative air humidity of 60 %.

Keywords

• blueberries
• air drying
• mathematical modeling
• freeze drying
• water activity