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

Drying of apple slices was studied in a conventional tray drier (initial slice thickness = 0.3 - 1.0 cm, drier temperature = 60 - 100 degrees C) and in a computer-controlled tunnel drier (initial slice thickness = 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 characterized by a constant rate period, followed by a falling rate period. The constant rate drying period did not occur, and the colour of the dried slices was improved substantially with tunnel drying under computer control, 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 surface in the constant rate drying period, which may serve as a medium for the reaction and transport of the chemical species.