| dc.description.abstract | Effect of amylase content and gluten on starch gelatinization and retrogradation
properties, and consequently bread staling, still is not clear. In the case of starch and
starch/gluten blends, information on the relationship between functional properties of
starch blends and amylase and gluten contents is scarce. Effects of amylase content on
baking and staling properties of bread were investigated by using 20, 30, and 40% blends
of waxy spring (WS) or waxy durum (WD) wheat flour with non-waxy wheat flour. Crumbs
with 30% and 40% waxy flour exhibited very open, porous structure. Retrogradation
enthalpies and bread firmness were higher for waxy than for non-waxy crumbs and higher
for WD than for WS crumbs at the end of storage (5 days), although waxy crumbs had a
higher amount of soluble starch (especially WD crumbs) than non-waxy crumb. Results
indicated that retrogradation and staling are complex processes that depend not only on
amylase content, but also possibly on interactions of starch with other crumb components
or interactions between two starches in a blend. To elucidate the effect of amylase content
and gluten on properties of starch, blends of WD starch (0, 12.5, 25, 50, 75, and 100%
w/w) and non-waxy starch, as well as starch blends combined with 30% gluten were
studied. Gelatinization and retrogradation properties, as well as properties of soluble
starch isolated from gels after 5, 10, 15, 20 days of storage and fractionated by gel
permeation chromatography (GPC}, were studied. Gelatinization enthalpy (11H) was higher
for blends with low than for blends with high amylase content. However, l).H was not
significantly different between each consecutive blend although their amylase contents
were different. Retrogradation enthalpy of starch blends (l).HaR) increased during 20 days of storage. On each storage day, M-laR was lower for low amylose blends than for high
amylose blends, showing that low amylose content in starch blends slowed the process of
retrogradation. Similar to t:.H, M-laR was not significantly different between each
consecutive blend. Apparently, gelatinization and retrogradation properties of starch
blends with different amylose contents were more complex than in single starches and
could not be interpreted as a simple sum of contributions of individual components. Gluten
did not affect gelatinization enthalpy of starch blends due to excess amount of water in the
system. However, it significantly lowered the M-laR of low amylose blends (50, 75, 100%
WO) compared to that of high amylose blends, especially on day 15 and day 20, which
was interpreted as the result of gluten interacting with branched starch molecules.
Analysis of GPC fractions of soluble starch showed that retrogradation patterns of O wx,
12.5 wx, and 25 wx blends were different, although their M-laR were similar. Low
proportion of branched fraction in O wx soluble starch after day 5 and low ratio of blue
value/total peak carbohydrate on days 15 and 20 indicated retrogradation due to
reassociation of branched molecules with long chains. In 12.5 wx and 25 wx soluble
starch, low values for the wavelength of maximum iodine absorption (Amax) of linear
fraction indicated that some amylopectin fragments eluted with the linear fraction.
Recrystallization of these molecules could have been facilitated by the presence of
amylase in the fraction. Gluten affected retrogradation pattern of starch by promoting
reassociation of branched molecules (reduction in A.max) at the beginning of storage. All
starch/gluten blends had similar retrogradation patterns. Overall, amylose content affected
gelatinization and retrogradation properties of starch significantly; however, in starch
blends these properties were not simple averages of properties of two starches. In
addition to the amylose content, properties of blends also could be governed by specific
interactions between two starches or between starch and gluten. | en_US |
