Term
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Definition
- Starch is found in plants including cereals,
roots, and trees
-Specifically, starch is found within the
endosperm within individual grains of cereal
-Cereal starches: rice, corn, wheat, and oats
-Root sources (produced commercially):
cassava (manioc) and potato (tuber)
-Tree starch: Sago starch from the pith of the
sago palm
-Legumes contain starch but not harvested
for their starch content |
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Term
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Definition
Native – found in original form
Special classes – waxy (almost 100% amylopectin –
do not gel but very good freeze-thaw characteristics)
and 80% amylose (used in edible papers/coatings) |
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Term
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Definition
Modified – modified by chemical or physical means
Physical treatments:
• Pregelatinization – precooked and dried No need to
heat for gelation to occur (used in instant pudding)
• Cold water swelling – hydrates very rapidly – used in
microwave cooking
• Spherical aggregates - spray-dried to form structures
that can trap up to 60% of their weight in flavors
prolonging shelf-life of product |
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Term
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Definition
Starch modification – chemical means
--*Thin-boiling*– treated with HCl or citric
acids to get acid hydrolysis
• Solubility is increased and viscosity decreased
and debranched amylopectin
• Used in making of gumdrops and gummy bears
-- *Oxidized* – reacted with sodium hypochlorite
to produce a thin hot paste and soft gel
• Limited use in food products
-- *Cross-linking*
-- *Starch phosphates* – esterification
with phosphates (sodium
tripolyphosphate)
-Molecules repulse each other
because they are charged
-Results in increased stability and
translucence and reduced syneresis. |
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Term
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Definition
--Amylose and amylopectin
--Relative amt of each determines the
behavior of the starch
• Cornstarch 24-28%
• Wheat starch 25-26%
• Potato starch 20-23%
• Tapioca starch 17%
• The other portion (generally 75-80%) is
amylopectin
• Commercially, high amylose content starches from
corn and rice are used in edible coatings |
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Term
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Definition
Predominately linear in nature (glucose
molecules joined by 1,4-α-linkages) but
forms loose coils in solution
Important because iodine can be trapped
within the coil turning the solution blue – this
is used to determine amylose content of
starch
2000-150,000 Daltons in molecular weight
Length of the amylose molecule varies by
starch – cereals have shorter amylose
molecules than roots/tubers
Slightly soluble – key characterisitic |
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Term
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Definition
Contains both 1,4-α-linkages and 1,6-
α-linkages resulting in dendritic spatial
arrangement (dense and bushy)
Molecular weight ranges from 65
million to 500 million daltons
Because it cannot bind iodine,
solutions with amylopectin will remain
purple-red in color
Waxy maize – all amylopectin |
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Term
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Definition
Amylose and amylopectin are deposited in
orderly fashion in the leucoplasts of the
plant cells.
The hilium is at the innermost layer of the
granule
Concentric layers of amylopectin (arranged
in growth rings), interrupted by some
amylose, are deposited in growth rings
Molecules within each layer and between
layers are held together by hydrogen
bonding in crystalline and amorphous areas
--Somewhat spherical shape and the
crystalline areas of the starch molecule
result in birefringence
- Birefringence is the refraction of light in two
slightly different directions
- It looks like a Maltese cross when viewed
under polarized light
-Only occurs in raw starch – in heated starch,
the crystalline areas are altered. |
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Term
| Starch Functional Properties |
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Definition
Gelatinization – pasting – implosion
Gelation – syneresis
Retrogradation
Dextrinization |
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Term
Gelatinization – the physcial
process |
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Definition
Process that results in thickening as starch
granules heated in water swell in size,
taking up water, and amylose migrates out
of the granule into the liquid
Viscosity of the mixture increases due to the
larger starch granules, reduced free water in
the mixture, and the addition in amylose
content now in the mixture
Birefringence is lost
Translucency increases starch mixtures to avoid
implosion |
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Term
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Definition
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Term
Gelatinization – Effect of
Temperature |
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Definition
---Rate of thickening varies by starch
Tapioca thickens at lowest temperature at
~71°C, wheat flour at ~83°C, and potato flour
at ~90°C.
---Thickening occurs gradually – no precise
temperature
Viscosity increases up to 100°C but
prolonged heating at 95°C or above results
in increased implosion and decreased
viscosity |
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Term
| Gelatinization – starch type |
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Definition
Thickening ability depends on the starch
source
Potato starch is a strong thickener but is not
heat stable and loses viscosity easily
Wheat – least effective (flour even more so)
Waxy maize – difficult to achieve thickening
but once it does viscosity remains stable
--- Translucence –
greatest in root starches (potato and
tapioca)
Waxy cereal starches more
translucent than regular cereal
starches
Increase in translucence is noticebale
in regular cornstarch as well as rice
and wheat starches
---Texture – ideally starch-thickened
mixtures should be smooth
Unmodified starches (esp root
starches) tend to be mucilaginous
Clearer (more translucent) starches
tend to be stringier
• Problems in palatability if texture is stringy
• This is why tapioca is pre-gelatinized |
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Term
Gelatinization – affect of
added ingredients |
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Definition
--- Sugar – competes with water with the
starch granule and cross-links with the
starch molecules
Gelatinization is delayed, gelatinization
temperature is increased as the level of
sugar is increased
Increased transulency
Reduced paste viscosity and gel strength
Disaccharide have more effect than
monosaccharides
--- Acid – especially below pH 4 along with
heat results in hydrolytic reactions that
break starch into shorter molecules.
Results in thinner paste than without acid
Rapid heating decreased time for acid
hydrolysis to occur
Add acid after gelatinization occurs
• The amt of liquid added after gelatinization occurs
needs to be incorporated into the recipe as this
portion will not be bound to the starch paste
molecules and could potentially dilute or thin the
paste if not accounted for
---Sugar and Acid – requires sufficient heat to
get complete gelatinization but care not to
continue heating or acid hydrolyisis will
result in paste thinning
Cross-linked starches are less susceptible to
acid hydrolysis
---Fats - reduce gelatinization and maximum
viscosity temperatures
---Milk proteins – lower maximum viscosity
temperatures |
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Term
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Definition
Gelation is the process by which starch gel
is formed.
Hot starch pastes exist as sols (solid
dispersed within a liquid) that exhibit flow
properties.
While hot, amylose moves freely and quickly.
As mixture cools, amylose moves more and
more slowly and stable hydrogen bonding
between amylose molecules results and a
gel is formed |
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Term
Gelation – types and
concentration of starches |
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Definition
--Starches low in amylose do not form
gels at normal level usage
Exception – 30% or more starch and
amylopectin can form a soft gel
---Cereal starches form firmer gels than
root starches
---Protein in wheat and other cereal
starches causes the gels to be rather
opaque rather than translucent |
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Term
| Gelation – extent of heating |
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Definition
Requires enough heat to release
enough amylose to form a gel network
but not too much that starch granules
fragment and the amylose is
hydrolyzed to smaller molecules
Prolonged heating (and vigorous
stirring) result in pasty texture and a
weakened gel structure |
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Term
| Gelation – effect of agitation |
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Definition
For maximum gel strength, starch
pastes should be allowed to cool
undisturbed
Agitation disturbs the H-bonds and
weakens the gel
Flavorings such as butter or vanilla
should be added in when paste is
removed form the heat and stirred in
before cooling the mixture. |
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Term
Gelation – effect of added
ingredients |
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Definition
Sugar – competes for water and results in a softer gel
with increased translucence
Acid – if added before gelatinization get softer gel due
to acid hydrolysis of amylose. If added after
gelatinization can get softer gel due to dilution
Fats – softer gels due to dilution and interference with
amylose interactions
Proteins – softer gels due to dilution. In the case of
egg yolk, if not heated sufficiently the alpha-amylase
within the yolk will act on the starch and breakdwon
the gel |
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Term
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Definition
Water is bound to the starch granule and
additional free water is trapped within the
starch gel structure.
held there by H-bonds
During aging, amylose molecules are drawn
closer together and some of the water is
“squeezed” out. Additional water is
released if the starch gel is cut with a knife
All of the water lost is termed syneresis |
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Term
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Definition
Retrogradation is the gradual process of
recrystallization of crystalline regions of
starch gels during storage due to the
amylose molecules reassociating with each
other more extensively
Results in gritty texture of the gel and
syneresis. Can result in staling (hardening)
of baked products
Can temporarily reverse but will reappear
and cooling occurs |
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Term
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Definition
Results from starch being heated in
dry form so that the starch is broken
down to shorter molecules
Occurs when flour is browned in a pan
by itself or with fat (ie brown roux) or
as a coating on foods to be cooked (ie
a flour coating on meat or fish prior to
pan-frying) |
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Term
| Starch – Food Applications |
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Definition
Thickening of sauces – gravies,
soups, soufflés, desserts, fruit
pies/cobbler fillings, binding agents
(croquettes, casseroles)
Fat binders in sauces
Formation of gels – puddings, pie
fillings
Cereals, pastas, pilafs etc. |
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