Microstructure changes
Fig. 3 presents both the structures of cross section and surface
of dehydrated noodle samples. With the increasing dehydration
temperature, pores were observed to appear gradually inside the
resulting noodles, specifically in the HTST samples. Homogeneously
distributed small pores were observed in the cross section
of noodle samples dehydrated under 120 C, and these pores
increased and grew larger in 135 C samples (Fig. 3a, highlighted
with black arrow); these observations were mainly caused by the
impact of the extremely rapid water evaporation induced by high
temperature, which was common in many dried foods (Zheng
et al., 2013). However, the structure surrounding the pores was
found to be more compact, which was similar to that reported by
Shi and Wang (2005), who explained that high temperature
promoted the development and constriction of gluten network,
further entrapping starch granules and leading to the continuous
matrix. Moreover, the adhesive effect of those gelatinized starch
could also give rise to the integration of noodle components.
Likewise, Fig. 3b showed that the surface of HTST samples presented
a more compact and continuous structure, compared with
the control and MTLT noodles. Changes in the structures of semidried
noodles partially explained the cooking and textural properties
as affected by MTLT and HTST dehydration.