3.6. Comparison of isolated starch and starch in situ
A comparison of in situ starch gelatinization from
different tissue zones with isolated starch is seen in Table
2. There were substantial differences in gelatinization
temperatures andtrans ition enthalpies between starch in
situ andisol atedstar ch. Gelatinization temperatures
were significantly higher for starch in situ in all tissues
studied. In addition, transition enthalpies were lower.
As for starch in situ, the gelatinization temperatures
were significantly higher in starch isolatedfrom pith
than from other tissue zones. However, no differences in
transition enthalpy were detected between starches
isolatedfrom the specific tissue zones. For isolated
starch samples, dry matter content was higher in pith
andlower in cortex than for tissue samples due to the
design of the experiment.
3.7. Retrogradation properties
Retrogradation properties were studied by analysing
the melting endotherm of recrystallized amylopectin by
DSC; thermograms are shown in Fig. 5. There were no
significant differences in onset, peak or conclusion
temperatures either for varieties or with time (Fig. 6). The mean melting peak temperature calculatedover all
samples was 57.3C, with a standard deviation of 3.6C,
andthe average melting range was 40.8C. Most
recrystallization within samples occurredd uring the first
48 h storage (Figs. 5 and7 ). The retrogradation process
continuedaft er this, but was then slower. Comparing the
varieties, Rocket hadthe lowest values of transition enthalpy andBint je the highest. Transition enthalpies for
Asterix and King Edward did not differ significantly.