However, it had been shown that the enthalpic transition was primarily
due to the loss of double helical order rather than crystallinity
(Cooke & Gidley, 1992). The enthalpy was an indicator of
uncoiling and dissociation energy of the double helices. In
Table 2, UP-LRS3 showed the highest Tp (117.9 C) and DH
(1346 J/g), while the Tp (117.1 C) and DH (565 J/g) was lowest
for MP-LRS3. These results were attributed to the proportion of
double helical structures of LRS3 through hydrogen bonds and
other intermolecular forces, which was consistent with the DD
value by FT-IR and PPA value by NMR. Among three samples, the
Tr value of MP-LRS3 (24.6 C) was the highest and UP-LRS3
(20.6 C) was the smallest. Difference in Tr reflected the extent of
heterogeneity of crystallites within the granules of GP-LRS3, MPLRS3
and UP-LRS3 (Li et al., 2011). PHI was the ratio of DH for
gelatinization to the gelatinization temperature range and a measure
of uniformity in gelatinization. The PHI value of UP-LRS3
(130.68) was for the greatest while MP-LRS3 was the smallest,
which was a result of greater amounts of double helices or stronger
interaction between starch chains within the crystalline domains
of UP-LRS3 compared to MP-LRS3. Therefore, the thermostability
of LRS3 was mainly affected by the double helical structure.