2.3. Experimental design and drying procedures
To compare the drying characteristics of IR and hot air drying,
banana slices were dried at three IR intensities, 3000,
4000, and 5000 W/m2 and hot air at 62.8 C. The weight
changes were measured every minute using a digital balance
during the drying. The 3000 W/m2 IR intensity had lowest
drying rate among the tested intensities. The 5000 W/m2 IR
intensity had the highest drying rate, but it caused discoloration
of finished products at high weight reduction levels.
Therefore, only 4000 W/m2 was then selected for producing
predehydrated samples for freeze-drying. Both dipped and undipped
samples were dried using IR to remove 20% and 40%
of the initial weight. The weight reduction levels were determined
for reasonably maintaining the texture integrity without
causing too much shrinkage after IR drying. The predehydrated
samples and a control sample without predehydration
were further dried using freeze-drying to a final moisture content
of about 5 g moisture/100 g wet weight for quality evaluation.
The evaluated quality parameters included color,
thickness shrinkage and crispness. All drying experiments