From Fig. 9, it is clearly shown that the xenon hydrate inside the
cells, intercellular space and middle lamella of the cells, as shown in dark spotted areas, decomposed as the temperature increased.
After the decomposition of xenon hydrate, the dark spotted areas
became xenon gas bubbles, and these bubbles were evidence that
the dark spotted areas were indeed xenon hydrate. The ice crystals
also melted, and it was found that the barley coleoptile tissues,
after xenon hydrate decomposition and the melting of the ice
crystals, could preserve the shape of the tissue. These results from
X-ray radiographic images suggested and confirmed that the CXF
process can preserve plant cells, because xenon hydrate formation
led to a reduction of bulk water within the cells and the water
surrounding the cells. During the freezing process, the bulk water
inside the cells and water surrounding the cells being transformed
into ice crystal was limited. Thus, cell and tissue damage due to
intracellular ice crystals and extracellular ice crystals was reduced.
The decomposition process of xenon hydrate and melting process
of ice crystals were observed for approximately 10 min, the temperature–time
profile, as shown in Fig. 10.
Furthermore, Fig. 11 shows that the ice crystals inside the cells
and the extracellular ice crystals, as shown in light grey, melted as
time and temperature increased. It was found that the barley
coleoptile tissues shrank after the melting of ice crystals because
the cell walls and cell membranes were damaged by ice crystal formation.
The main cause of cell damage was by extracellular ice
crystals, which led to water from the cells to migrate because of
osmotic pressure (De Ancos et al., 2012). In general, freezing food
tissues can lead to extracellular ice because the water surrounding
the cell freezes before the cell contents, due to the fact that the
cytoplasm is more concentrated than the liquid of the extracellular
area of the cells and because, thermodynamically, the component
with the largest volume will nucleate first (Dumont et al., 2004;
Zaritzky, 2012). This melting process of ice crystals was also
observed for approximately 10 min, the temperature–time profile,
as shown in Fig. 10.
From those X-ray radiographic images it was found that the
results corresponded with the self-diffusion coefficient and permeability
of cell membrane results. In the case of the CXF sample
being able to maintain a typical restricted diffusion phenomenon
and permeability of the cell membranes in barley coleoptile cells,
this was confirmed by the X-ray radiographic images. On the contrary,
the restricted diffusion phenomenon in the FAP sample was
destroyed and the permeability of cell membranes increased,
which was also confirmed by the X-ray radiographic images.