(b) the effect of condensed water vapour with salt particles on the surface of tray
thereby increasing the salinity of condensed water and reducing
moisture absorption rate of the tray. Condensation occurs when
temperature of the surface falls below the dew-point temperature
of the air within the package headspace. Anti-condensation
films
commonly used by the industry help to decrease the surface
tension of the water droplets that form on the
film’s surface. This
reduces the contact angle of the water molecules, and the water is
able to spread out more creating a more uniform layer of water,
thus only transforming visible water droplets into invisible water
layer. This helps to improve the transparency of the
film surface but
not completely eliminating condensation. Moreover, mushrooms
continue to produce moisture even at 100% RH, thus there are
equal number of molecules evaporating from the mushroom
surface as there are condensing back into the package headspace.
Thus, the amount of condensed water inside the package
headspace increases over the storage period. The morphology of
the outer tissue structure and also phenomena of super-saturation
needs to be further explored in order to explain the condensation
behaviour in fresh produce packaging.
Under the saturated humidity conditions, the water vapour
flux
from the package headspace to storage environment is dominated
by the limiting step of the
film resistance to transport. The water
vapour permeability of the polypropylene
film used for control and
humidity-regulating tray was the same but still the experimental
data showed the difference in the amount of water transmitted
over the
film. Control-PP tray transmitted 1.3 g of water vapour into
the storage environment (85% RH); whereas the humidity-
regulating tray transmitted significantly lower amount of water
vapour (0.8 g). This was due to the lower RH observed inside the
humidity-regulating tray (93% RH), therefore, lower driving force
for water vapour than the control tray (100% RH).