Starch retrogradation properties of cooked rice were analyzed
by a Perkin Elmer pyris 6 differential scanning calorimeter (DSC)
(Perkin Elmer, USA). The DSC was calibrated with indium (melting
point¼156.6 C, DHf ¼28.6 J/g) and an empty pan was used as
a reference. The cooked rice samples were prepared using the
methods of Kim, Kim, Shin, and Kwangiu (1997) and Yu et al.
(2009, 2010). After textural properties determination, the
samples of cooked rice was mixed with 99% ethanol (1:4, v/v) and
dehydrated for 12 h. Then the mixture was passed through
a Büchner funnel, and dried at 37 C in an air oven for 24 h. The
dried cooked rice was passed through a 100-mesh (0.147 mm)
sieve after milling by a universal high-speed smashing machine
(FW80-1, Tianjin Taisite Instrument Co. Ltd, China). A total weight
of 4.0 mg cooked rice samples (dry basis) and distilled water (1:2,
w/w) was placed in pre-weighed aluminum sample pans (PE0219-
0062). The pans were sealed hermetically to prevent moisture loss
and kept overnight. For all DSC runs, a sealed empty aluminum
pan was used as reference. The sample was held isothermally at
20 C for 1 min before being heated from 20 to 140 C at 10C/
min. The peak temperature and the enthalpy (DHr, J/g) associated
with the retrograded starch melting peak appearing between 40
and 70 C were calculated. The DHr is used to indicate the enthalpy
of amylopectin starch retrogradation. The DSC measurements
were performed in triplicate. The results were presented as mean
values.