From Table 1, for banana slices fried at 110 C, there is a significant
shrinkage in the product diameter during the first 5 min of
frying, indicating a rapid water loss. The moisture content in the
product decreased dramatically from 74% (w.b.) to 44% (w.b.). This
results correlates with a typical drying process in which water is
removed from the porous structure and the cell walls collapse under
compressive stress (Demirel and Turhan, 2003; Kraisheh et al.,
2004; Panyawong and Devahastin, 2007; Nimmol et al., 2007).
However, after approx. 5 min of frying, the degree of shrinkage decreased.
Nimmol et al. (2007) suggested that the effect of casehardening
(rigid layer) at the product perimeter may retard the degree
of shrinkage. In addition, once a crust region began to form at the
product surface and its perimeter, the product may have expanded
in the axial and radial direction as gaseous vapor expanded, causing
a pressure buildup. Similar results can be seen for the thickness
expansion of the product. The thickness of the banana chips decreases
by nearly 20% after 5 min of frying. Once the crust had been
formed and gas pressure buildup occurred inside the product, the
product expanded by as much as 20% at the end of the frying process.
Yamsaengsung and Moreira (2002b) observed similar effects
of puffing due to pressure buildup inside the product for superheated
steam drying of tortilla chips.