COLOR-CHANGE AND WEIGHT-LOSS OF APPLE SLICES DURING DRYING

Drying of apple slices was studied in a conventional tray drier (initi al slice thickness = 0.3 - 1.0 cm, drier temperature = 60 - 100 degree s C) and in a computer-controlled tunnel drier (initial slice thicknes s = 0.8 cm, air temperature = 50 - 100 degrees C, air flow rate = 2.4 m/s). In most of the experiments the drying behaviour was characterize d by a constant rate period, followed by a falling rate period. The co nstant rate drying period did not occur, and the colour of the dried s lices was improved substantially with tunnel drying under computer con trol, when a linearly decreasing temperature profile from 100 degrees C to 70 degrees C was used. The quality improvement may be attributed partly ot the elimination of the continuous water film covering the su rface in the constant rate drying period, which may serve as a medium for the reaction and transport of the chemical species.