Comparative Study of Different Process Conditions of Freeze Drying of ‘Murtilla’ Berry

Abstract

Different operating conditions for drying halves of ‘Murtilla’, a native Chilean berry food species, were studied in atmospheric freeze drying, using dry air through a pulsed fluidized bed, and vacuum freeze drying. Applying a 23 experimental design, the effect of the freezing rate, the air temperature, and the application of infrared radiation was studied on the moisture content and the drying time. Fast freezing with infrared (IR) and air at 15°C for the second drying stage allowed achieving final moisture contents similar to vacuum freeze drying in equivalent total drying periods. Drying at the same conditions except with air at 5°C resulted in a larger preservation of antioxidant capacity of the fresh fruit. Also, the texture was adequate for a dry fruit, with a pleasant flavor for direct consumption or mixed with yogurt. The drying kinetics of the first drying stage was modeled by an equation based on the uniformly retreating ice front model, which gave a reasonable description of the trend for this stage, although it does not include the application of IR radiations or the rate of freezing. The Page equation was an adequate tool to represent the second drying stage (which started after 7 h) for each experimental run, by using specific parameters (n and k) obtained by fitting the experimental data. The parameters exhibited similar values to those cited in the literature for foods.