2.4. IR and hot air predehydration
A catalytic infrared (CIR) dryer/dehydrator equipped with
two catalytic IR emitters powered with natural gas (Catalytic
Infrared Drying Technologies LLC, KS) was used in this
study. The CIR dryer consisted of infrared emitters of area
30 60 cm with a wave guard around the IR emitters to prevent
infrared radiation from escaping and to keep heating uniform.
With the wave guard, the heating area was 34 64.5 cm.
The drying tray was placed in between the two IR emitters in
parallel position of the emitter face. Banana slices were heated
from both the top and bottom sides. An automatic data acquisition
and control system developed in our laboratory was used
to control and record various operation parameters. The schematic
diagram of the equipment is shown in Fig. 1. The IR
dryer was operated with a continuous heating mode. For the
continuous heating, the natural gas was continuously supplied
to the emitters. The continuous heating could take advantage
of delivering high heat to the product in a relatively short
time for quick drying. The change in sample weight during
the drying process was measured using a digital balance until
at least 40% weight reduction was reached.
Banana slices were arranged in a single layer on the drying
tray (metal screen) which was sprayed with PAM cooking
spray to prevent bananas from sticking to the tray. The banana
slices were placed within the confines of the wave guard at
a loading rate of approximately 2.1 kg/m2. After infrared predehydration,
the banana slices were transferred to wax paper
by flipping the drying tray and then transported to a large scale
air blast freezing system with temperature of 18 C.
For comparison, a hot air dryer of Proctor & Schwartz Cabinet
Dryer (Product code 062, Proctor & Schwartz, Inc., Horsham,
PA) was also used to dry the banana samples to obtain
the drying curve. The hot air dryer was set at 62.8 C and the
sample weight changes were also measured using a digital balance
during drying.