Accordingly, Altan et al. (2008) stated that extrusion cooking of
cereal raw materials results not only in expanded volume, but also
in microstructural modification. In our study the pictures show
considerable differences in the cellular structure depending on
feed moisture and barrel temperature. The microstructure was
found to depend on the cell size and their organization. Rye extrudates
show a porous structure with numerous, irregular air cells.
Apparently, the higher feed moisture content with low barrel temperature
results in thicker cell walls (Fig. 10(b)). Similar results
have been found for pea extrudates (Rzedzicki and Fornal, 1999)
and corn–lentil extrudates (Lazou and Krokida, 2010). Moreover
we can observe that while bulk density was higher, corresponding
to the collapse of the expanded structure, the foams became denser.
Jin et al. (1995) and Lazou and Krokida (2010) suggested that
the more expanded the extrudates would have larger cells with
thinner cell walls than the denser and less expanded products.
The increase in extrusion temperature resulted in the formation
of more air cells and thinner cell walls (Fig. 10(c) and (d)). Extrudates
at lower temperature show fewer cells but larger in size
compared to those at the higher temperature.