J. Silverio et al., The effect of temperature cycling on the amylopectin retrogradation of starches with different amylopectin unit-chain length distribution, CARBOHY POL, 42(2), 2000, pp. 175-184
The amylopectin retrogradation of six cereal starches (wheat, rye, barley (
normal-amylose, high-amylose and waxy), and waxy maize), three potato starc
hes (two normal-amylose, and a high-amylopectin potato), and a single pea s
tarch was studied by differential scanning calorimetry (DSC). The recrystal
lization of amylopectin was measured after 2 and 4 days of storage. In orde
r to affect the crystallinity of the amylopectin, samples were exposed to d
ifferent temperature cycles during the storage period, favouring the nuclea
tion or the propagation of the crystallites. The temperature cycles during
the first 2 days were: 24 h at 6 degrees C (facilitating nucleation), follo
wed by 24 h at either 30 or 40 degrees C (promoting propagation). For the 4
days storage test the temperature cycles were repeated. Moreover, the amyl
opectin unit-chain length distribution of the starches was determined by hi
gh-performance anion exchange chromatography (HPAEC) after debranching of i
solated amylopectins.
The recrystallization of amylopectin was greatly affected when gelatinized
starch was treated with different time-temperature cycles. The melting enth
alpy of recrystallized amylopectin (Delta H) decreased in most cases. The o
nset temperature of melting of recrystallized amylopectin (T-o) was control
led by the propagation temperature (T-p), and increasing the latter resulte
d in an increase in T-o. As a result of the increase in T-o, the melting ra
nge of the recrystallized amylopectin (Delta T-r) decreased. A development
of crystallites that melted at higher temperatures, noticed as an increase
in the offset temperature (T-f) of melting, was observed for the cereal sta
rches after all temperature treatments. The possibility of predicting how a
specific T-p would affect and increase the T-o of recrystallized amylopect
in when gelatinized starch was treated with the two day cycles was demonstr
ated.
The DSC and HPAEC results showed that amylopectin unit-chains with DP 6 and
the population of chains with DP 18-19 were positively correlated to Delta
H, whereas the correlation to the population of chains of DP 8-11 was nega
tive. Indications of a negative correlation between Delta H and chains of D
P 22-34 as well as a positive correlation to chains with DP > 40 were also
found. The changes found in T-f correlated to the same distinct amylopectin
populations as the previous ones for the relation to Delta H. However, the
signs of the correlation coefficients were changed. (C) 2000 Elsevier Scie
nce Ltd. All rights reserved.