Effect of Operating Conditions in Atmospheric Freeze Drying of Carrot Particles in a Pulsed Fluidized Bed

Abstract

Drying kinetics and shrinkage of carrot particles during atmospheric freeze drying in a pulsed fluidized bed were studied by using a 24 factorial statistical design as a function of particle size (6 mm × 6 mm × 1.5 mm and 6 mm × 6 mm × 3 mm), freezing rate (slow and quick), air temperature (−15 and −5°C), and type of energy supply (convective and convective with infrared radiation). Then, a programmed air temperature was applied, namely, −15°C during the first 5 or 6.5 h, followed by either 0 or 5°C. The results were compared with those obtained by vacuum freeze drying at constant temperature throughout the process. An important reduction in drying time was obtained by using higher air temperature in the second stage of the drying process.