Change of Moisture Content of Banana Slices
During Puffing
The initial moisture content of fresh bananas was
approximately 284.60.7% (db). After citric acid or sodium
metabisulfite pretreatment for 5 min, the sample moisture
content was increased to 333.60.9% db for 2.5-mm-thick
slices and 373.50.4% (db) for 3.5-mm-thick slices. Then
the samples were blanched with hot water and the sample
moisture content was increased to 351.50.7% (db) and
396.70.9% (db) for 2.5 and 3.5mm thicknesses, respectively.
The increase in moisture content during blanching is
due to partial disruption of sample cells and swelling of
banana starch.[23] Figure 3 shows the evolution of banana
moisture content during processing steps. Blanching provided
a longer drying time in the first stage and the drying
time for the blanched sample was 5–10 min longer than that
of the unblanched sample. The drying times for each processing
step are shown in Table 1.
During the puffing step (B) shown in Fig. 3, the moisture
content of 2.5-mm-thick samples for the unblanched case
decreased faster than that of the 3.5-mm-thick sample. As
determined from the experiment after the puffing step,
the moisture contents were decreased to 14.2 and 10.3%
(db) for the samples with 3.5 and 2.5mm thicknesses,
respectively. The lower moisture content in the thinner
sample is due to the shorter distance for moisture to travel
to the exterior surface.