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fatty acid methyl esters (FAME), were 0.07-0.17 g
100 g −1 , signifi cantly lower than normal starch
(Yasui et al., 1996). Interestingly, waxy wheat
endosperm contains more fat than normal wheat
starch (1.0% vs. 0.8%), but waxy starch granules
contain much less fat (0.2% vs. 1.0%) (Yasui
et al., 1996; Lumdubwong and Seib 2001). The
lower lipid content in waxy wheat starch permits
conversion into a family of high and low molecu-
lar weight maltodextrins that do not become
rancid during drying and storage (Lumdubwong
and Seib 2001).
After gelatinization, starch can retrograde
during storage. Hayakawa et al. (1997) found that
when stored at 4 ºC for one to three weeks, waxy
wheat starch (20% solids) retrograded signifi -
cantly less than normal wheat and waxy maize
starch. In contrast, Yoo and Jane (2002) reported
that after storage at 4 ºC for a week, the endother-
mic enthalpy value of melting for retrograded
waxy wheat starch (33% solids) was higher
(4.6 J g −1 ) than that of one commercial wheat
(3.8 J g −1 ), and similar to that of another normal
wheat ('Centura') starch. The percentage retro-
gradation (Δ H retrogradation H gelatinization × 100) of
waxy wheat, Centura wheat, and the commercial
wheat starch was 33.7%, 45.1%, and 35.9%,
respectively. In addition, Sasaki et al. (2000)
studied the effects of amylose content on gelati-
nization, retrogradation, and pasting properties of
wheat starch and found that the enthalpy value
for retrograded starch correlated negatively with
amylose content. Guan et al. (2007a) studied waxy
wheat starch isolated from waxy hard wheat and
found that the enthalpy values of the retrograded
waxy starch (25% solids, after storage at 4 ºC for
7 days) was signifi cantly lower (about 2.0 J g −1 )
than that of waxy maize starch (5.9 J g −1 ) and
normal wheat starch (4.8 J g −1 ) as measured by
DSC (L. Guan, pers. comm.). More research
should be conducted to clarify the cold storage
stability of cooked waxy wheat starch and compare
it with waxy maize starch and normal wheat
starch.
The molecular structure of waxy wheat has
been compared with that of normal wheat and
other waxy starch types. Using high-performance
anion exchange chromatography (HPAEC),
Yasui et al. (1996) reported that the chain-length
distribution profi les of the amylopectin fraction
of waxy wheat lines were similar to their wild-
type counterparts. Yoo and Jane (2002) studied
the molecular structure of starch isolated from
waxy wheat, amylose-reduced wheat, and wild-
type HRW wheat, and showed that the peak
chain-length among all starch types was at DP
12, as determined by HPAEC. However, average
chain-lengths varied between DP 23.5 and 24.9.
Waxy wheat amylopectin had no detectable
extra-long branch-chains relative to amylopectin
of normal wheat starch, but its molecular weight
was greater.
Waxy wheat fl our exhibits aberrant falling
numbers independent of α-amylase activity
(Graybosch et al., 2000; Abdel-Aal et al., 2002).
Evidence indicates that starch granules in waxy
wheat fl our are more fragile and subject to break-
down under heat and mechanical shear, and they
give a low-consistency fl our slurry in the falling
number test (Abdel-Aal et al., 2002; Chibbar and
Chakraborty 2005). Waxy wheat starch generally
displays a lower pasting temperature but higher
peak viscosity than waxy maize starch and normal
wheat starch as measured by a rapid viscoanalyzer
(Kiribuchi-Otobe et al., 1997; Yasui et al., 1999;
Grant et al., 2001; Yoo and Jane 2002; Abdel-Aal
et al., 2002; Kim et al., 2003). Differences in
pasting temperature and peak viscosity between
waxy and normal wheat starches were signifi -
cantly greater than the difference between their
maize starch counterparts (Yoo and Jane 2002).
Using a hot-stage microscope, Guan et al. (2007b)
confi rmed that waxy wheat starch granules began
to swell at a lower temperature, exhibited higher
swelling power, but eventually fragmented into
smaller pieces. In contrast, normal wheat starch
granules retained a rounded shape even after
being heated to 90 ºC, presumably because the
amylose-lipid complex restricted swelling of
granules in normal wheat starch (Tester and
Morrison 1990). Guan et al. (2007a) heated waxy
wheat starch in water on a hot-stage microscope
and recorded changes in morphology of waxy
wheat granules continuously during heating.
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