HTST Pre-Drying Influence on Vacuum Drying Kinetics and Carrot Slices Quality Parameters Evaluation

Abstract

High-temperature and short-time pre-drying followed by vacuum drying was carried out in order to dry carrot slices. In a pre-drying process, a central composite rotatable design was tested where drying air temperature (114–156C) and time (540–1,740 s) were independent variables of effective diffusivity, and water activity and rehydration capacity were dependent variables. Then absolute pressure (0.09 MPa) and drying temperature (70C) were kept constant. For rehydration capacity optimal conditions, the color and β-carotene degradation were evaluated and compared with fresh samples. The effective diffusivity values with and without shrinkage effect ranged from 5.37 × 10−12 to 6.55 × 10−11 and from 8.50 × 10−12 to 8.44 × 10−11, respectively. Water activity of dried products ranged from 0.39 to 0.44 and rehydration capacity between 58.16 and 84.40%. Dried carrot brightness values were noticed to be lower than those of fresh samples, besides the reduction of red and yellow values. The β-carotene degradation was also observed. Practical Applications In studying the drying process of biological materials, the shrinkage effect must be analyzed for a better understanding of transport phenomena. For processed products, the knowledge of shrinkage, water activity, rehydration capacity as well as property changes (color and β-carotene) caused by drying process is very important. These properties can provide an important information set to determine the process conditions in order to obtain a good quality of food, as well as their characterization and stability prediction.