The reason for choosing cassava and potato starches was to
study the effect of NaCl on two polymers being different in terms of
the charge on the molecules. Potato starch is a charged molecule
(the amylopectin is phosphorylated) while cassava starch is not.
The results showed that in principle the plasticizing effect of NaCl in
both cassava and potato starches was seen and therefore the
mechanism would be similar.
studied the thermal transitions of osmotically dehydrated tomato
at low moisture levels by modulated temperature DSC and reported
that compared to the control the presence of sucrose and NaCl in
the dried tomatoes had a negative effects on the glass transition.
For example for completely dried tomato samples, the inclusion of
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4.6% NaCl caused a 15 C depression of the Tg. They also stated that
NaCl changed the sorption characteristic of the dried tomato
significantly particularly at relative humilities greater than 50%. The
result was related to the impregnation of the solid matrix with
a solute of lower molecular weight. NaCl also has been reported to
decrease the glass transition of bovine serum albumin in dilute
solutions (Inoue & Ishikawa, 2000). Dielectric relaxation studies of
frozen wheat dough with and without NaCl have also indicated that
salt can depress the glass transition and the onset of melting
temperature of ice in frozen dough (Laaksonen & Roos, 2001) and
the effect seen was thought to be due to the higher conductivity of
the frozen material with salt.
There is very little information on the mechanism of glass
transition depression by NaCl. At low moistures’ levels as studied in
this research (