AIR IMPINGEMENT DRYING CHARACTERISTICS AND QUALITY OF CARROT CUBES

The effects of air temperature (40, 50 and 60C), air velocity (3.0, 8.0 and 13.0 m/s) and air relative humidity (10, 20 and 40%) on air impingement drying characteristics of carrot cubes and the quality of dried carrots were investigated. The drying experiments were carried out according to orthogonal design method on the air impingement dryer. Results indicated that drying time of carrot cubes was more affected by drying air temperature, followed by air relative humidity and air velocity. The moisture effective diffusivity calculated from the second Fick's law of diffusion ranged from 0.265 x 10-9 to 1.052 x 10-9 m2/s. The activation energy determined from the slope of the Arrhenius plot, ln(D-eff) versus 1/(T + 273.15), was 20.17 kJ/mol. The color values L (white/dark), a (red/green) and b (yellow/blue) of the samples decreased from 50.02 to 32.71, 32.49 to 14.34 and 35.52 to 16.38 separately when the drying temperature increased from 40 to 60C. Rehydration experiments demonstrated that the rehydration ratio of dried carrot cubes was significantly affected by drying air temperature and air relative humidity. The surface microstructures of dried carrot cubes were observed using a scanning electron microscope, which showed that the outer layers of the samples dried at 60C drying temperature and 10% air relative humidity had more consolidated rigid and denser structure than the samples dried at 40C drying temperature and 40% air relative humidity. PRACTICAL APPLICATIONS Air impingement drying is used for food and agricultural product processing. But, it is a complicated process. Many factors such as drying temperature, air velocity and relative humidity can influence its drying characteristics and quality. Carrot is a typical vegetable, which is sensitive to microbial spoilage and deterioration reactions. Using drying technology can prolong its shelf life. Investigating air impingement drying characteristics and quality of carrots can help to understand its drying process and the effect of drying parameters on drying quality. This research was done to provide enough information to build a commercial impingement drying system.