Agriculture Reference
In-Depth Information
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Resistance of starch pastes to breakdown.
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Viscosity by acids, heat and/or mechanical shear.
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Retrogradation tendencies.
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Ionic character.
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Hydrophilic character.
Taking pasting temperature as an example, this is an important characteristic in the
processing of starch and starch products. If starch granules in suspension in water are
heated, water penetrates the granules to hydrate them with resulting swelling. If the
temperature of the starch suspension or slurry is heated above its pasting temperature,
a viscous mass is produced and the starch granules lose their unique microscopic
appearance or shape, which may not be regained upon cooling to room temperature.
As starch granules are heated in water they hydrate and swell, the refractive index of
the granules approaches that of water, and the initially opaque slurry becomes more
transparent. In general, the pasting temperatures of modifi ed starches are lower than
those of native starches. This is important in some applications, for example, to keep
fruit pieces suspended in a fi lling while it is cooking.
7.7.1 Types of modifi cation
While it is not possible to detail in full every type of modifi cation, some of the
more common modifi cations are set out in Table 7.4. The modifi cation of native
starch may involve a change in physical form, a controlled degradation and/or the
introduction of chemical groups. Table 7.5 sets out the modifi ed starches permitted
for use in EU in foods together with their applicable E numbers, which must be
present on the label.
Table 7.4
Types of modifi cation
Type of modifi cation
Reason for modifi cation
Treatment
Dextrin
Adhesion, low viscosity
Dry heat and treatment
with acid
Acid modifi ed starch
Low viscosity, strong
viscosity stability
Acid hydrolysis
Alkaline modifi ed starch
Low viscosity, strong
viscosity stability
Treatment with sodium or
potassium hydroxide
Bleached starch
Low viscosity, strong
viscosity stability
Treatment with hydrogen
peroxide
Oxidised starch
Low viscosity, strong
viscosity stability
Oxidation with sodium
hypochloride
Enzymatically modifi ed
starch
Low viscosity, strong
viscosity stability
Treatment with alpha
amylase
Cross-linked starch
High shear, acid stability
Hydroxyl bonding
Stabilised starch
Improved viscosity stability
Esterifi cation
Combinations of above
Specifi c properties
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