Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
potato starch has unique gelatinization properties, a low gelatinization temperature
with a narrow range, and a slow retrogradation rate.
The gelatinization temperature of Naegeli dextrin prepared from normal maize
starch is higher than that of native starch, 23 but the gelatinization temperature of
Naegeli dextrin prepared from waxy maize starch is lower than that of native starch.
The difference indicates that amylose in the normal maize starch may have retrograded
during acid hydrolysis; the retrograded amylose causes increase in the gelatinization
temperature of normal maize Naegeli dextrin.
Crystalline spherulites of A- and B-type polymorphisms, prepared from a short
chain amylose (DP 15), show different melting behaviors. 72,73 The melting temperature
of the B-type crystallite is about 20°C lower than that of the A-type crystallite
when measured at a constant water content. This indicates that the A-type structure
is the more stable of the two polymorphs. 74,75
Gelatinization of starch can also be achieved by using aqueous alkaline solutions
(e.g., NaOH, KOH); dimethyl sulfoxide; and various neutral salt solutions such as
CaCl 2, LiCl, KI, and KSCN. 76,77 Saturated LiCl and CaCl 2 solutions are known to
gelatinize starch at the periphery of the granule. 58,59,78 Thus, the solutions can be
used for controlled surface gelatinization. 58,59,79 KI and KSCN are known to have a
water structure-breaking effect. Consequently, aqueous solutions of KI and KSCN
are less viscose and can easily penetrate into starch granules and gelatinize starch
from the hilum. 77
Sodium sulfate is commonly used to stabilize starch granules during chemical
reactions at an alkaline pH for manufacturing chemically modified starches. 5 Sodium
sulfate increases the gelatinization temperature of starch granules through its structure-making
effect and its large negative charge density. 77 In the presence of a high
concentration of sucrose, starch gelatinization temperature increases substantially. 80
As a result, cakes containing large concentration of sugar sometimes collapse when
removed from the oven after baking. This is attributed to starch in the cake batter
not being fully gelatinized during baking and failure to develop the structure that
holds the volume of the cake. Chlorine-treated flour containing oxidized starch is
preferred for cake batter because oxidized starch has a lower gelatinization temperature
and is more prompt to gelatinize to develop the structure, which prevents cake
collapsing. Starch in sugar cookies is frequently found ungelatinized, resulting from
large concentrations of sugar and lipids and little moisture content in the cookie
dough.
7.4.2 PASTING OF STARCH
Pasting is an important function for many applications of starch, such as thickening
agents and sizing agents. Different starches display different pasting properties. 40
Pasting properties of starch depend on the amylose and lipid contents and branchchain
length of the amylopectin. Cereal normal starches, consisting of amylose and
lipids, display higher pasting temperatures and less peak viscosity and less shear
thinning than do their waxy starch counterparts. 40 Normal starches, containing amylose,
display greater set back viscosity. Species and contents of lipids of the starch
significantly affect pasting properties. For example, normal wheat starch consists of