Osmotic dehydration of pumpkin before freeze-drying process
does not change significantly the water content of investigated
samples in comparison to pumpkin without osmotic pre-treatment.
Also elongation of duration from 3 to 20 h has no effect on the
investigated index. However, osmotic dehydration caused the
A. Ciurzynska et al. / LWT - Food Science and Technology 59 (2014) 1075 e1081 1079
increase of water activity of samples osmotically dehydrated in
comparison to pumpkin without osmotic pre-treatment. Elongation
of osmotic dehydration duration had a significant effect on the
decrease of water activity for freeze-dried pumpkin. Osmotic pretreatment
as well as elongation of duration in most cases does
not influence the sample colour, because differences in analysed
colour indexes were statistically insignificant.
In most cases the use of blanching does not change the water
content and activity of samples in comparison to unblanched
pumpkin. Similar effect was observed for colour coefficients for
which differences were statistically insignificant. Decrease of
freezing temperature (70 C), which facilitated the removal of
water during freeze-drying process caused the decrease of water
content and activity, as well as for colour coefficients in comparison
to samples frozen at a temperature of 18 C, but for colour coefficients
results were not statistically significant.