Starch
Megan Erickson
Central Washington University
What is it?


Complex carbohydrate made up of two
components
Components:
– Amylose
– Amylopectin

Properties depend on amounts of the
components
Where is it found?

Roots/Tubers
– Potato
– Arrowroot
– Tapioca

Cereal
–
–
–
–
–
Corn
Waxy corn
Wheat
Rice
Waxy rice
Amylose


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Linear component
of starch
Contains 1,4alpha-glucosidic
bonds
Molecular weight:
less than 0.5
million
Can form coils
which will trap
iodine and turn
blue
Amylopectin




Branched
component of starch
Contains 1,4-alphaglucosidic as well as
1,6-alpha-glucosidic
bonds
Molecular weight:
50-500 million
Limited coiling
causes purplish-red
color when iodine
added
Amylose vs. Amylopectin


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Starches usually contain more
amylopectin than amylose
Generally roots/tubers contain more
amylopectin than cereals
Roots/Tubers: 80% amylopectin
Cereals: 75% amylopectin
Waxy corn and rice contain virtually all
amylopectin
Starch Composition
Starch
Tapioca
Potato
Wheat
Corn
Waxy corn
Hi amylose
Rice
% amylose % amylopectin
17%
83%
~20%
~80%
25-26%
~75%
24-28%
~75
~0%
~100%
~ 75%
~ 25%
22%
78%
Starch Granule


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Made in the cytoplasm of plant cells
Amylopectin forms in concentric circles
with amyose dispersed in between
Held together by hydrogen bonds
The granule swells when heated in
water
Starch Granule
Functions

Gelatinization
– Structure in baked products
– Thickener in sauces, soups, and dressings


Dextrinization
Gelation
– Pie filling
Gelatinization




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When starch is heated in water
Hydrogen bonds break, allowing water to
enter the granule and the granule swells
Amylose migrates out of the granule
H-bonding between water and amylopectin
increases
Reduced free water changes the viscosity of
the starch mixture, thickening it
Gelatinization and
Temperature


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Gradually thicken with temperature
Can be heated to 100oC without much
granule rupture
If held at 95oC will implode and lose
viscosity
Gelatinization and Type of
Starch



Best thickening
ability: potato
starch
Worst thickening
ability: wheat starch
More
amylopectin=more
translucent=more
stringy
Viscosity and Type of
Starch
Gelatinization and Sugar

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Used together in pie fillings and puddings
Sugar competes with the starch for water so
less water available for gelatinization
Delays gelatinization and decreases viscosity
Increases gelatinization temperature
The more sugar added, the longer the delay
Disaccharides have a stronger effect than
monosaccharides
Gelatinization and Acid


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Used together in fruit pie fillings,
specifically lemon fillings
Acid breaks down starch molecules so
the paste is thinner
Decreases viscosity
Acid effect can be minimized by
adding after gelatinization or heating
rapidly
Gelation


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As a starch paste cools, a gel is
formed
Free amylose molecules lose energy as
the temperature decreases and form
hydrogen bonds
The bonds create a network that holds
the swelled granules in place
Gelation and Starch
Source



The more amylopectin (less amylose),
the softer the gel
Potato starch=high amylopectin=good
thickening agent=soft gel
Corn starch=less amylopectin=less
effective thickening agent=strong gel
Gelation and Other
Effects

Heating
– Moderate temperature and rate of heating
– Enough amylose needs to be released from the
granule without the granule bursting

Agitation
– Agitation during cooling disrupts amylose
network
– Should mix flavorings immediately after
removing from heat
Gelation and Other
Effects

Sugar
– Decreases gelatinization and amylose
release
– Softer gel

Acid
– Decreases gelatinization by hydrolysis of
granules
– Softer gel
Aging Gels

Syneresis
– Loss of water from a gel
– Amylose molecules pull together, squeezing
water out

Retrogradation
– Realignment of amylose molecules
– Hydrogen bonds break and reform into more
orderly crystals
– Can by reversed by gently heating
– Examples: refrigerated pudding, stale bread
Dextrinization



When starch is heated without water
A higher temperature is reached than
with water
Bonds break throughout the starch
forming dextrins
Genetically-modified
Starches

Waxy starch
– High in amylopectin
– Used in fruit pies because thickens well, but
does not gel well
– Have good freeze-thaw stability

High amylose starch
– Amylose creates strong bonds to form strong
gels
– Used in edible films to coat food
How to compare
starches?

Line spread test:
– Measures thickening power
– Poor heated starch into cylinder, lift cylinder and
measure spread after specified time using
concentric circles

Universal Texture Analyzer:
– Measures gel strength

Percent sag:
– Measures gel strength
– Measure molded gel height and compare to
unmolded gel height
– Stronger gel=small % sag, weaker gel=large %
sag
Modified Starches


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Physically or chemically modifying native
starches
Are used for specific applications in the food
industry, Why?
Native starches have undesirable qualities:
– Poor processing tolerance to heat, shear and
acid
– Poor textures
– Do not store, hold, and freeze/thaw well
Pre-gelatinized Starches

Use:
– Instant pudding
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Dehydrated gelatinized starch
–
–
–
–
Heated so granule swells and then dehydrated
Swells when water added, no heat necessary
Decreases preparation time
Physical change
Thin-Boiling Starches

Use:
– Pass freely through pipes

Acid-hydrolyzed starch
– Hydrolyzes 1,6-alpha-glucosidic bonds
– Amylopectin in smaller pieces
– Decreases thickening power, but makes a
strong gel because hydrogen bonds form
more readily
Cross-linked Starch

Use:
– Increases storage time because of reduced
retrogradation
– More stable at high temperature, with agitation,
and with acid addition
– Salad dressings, baby foods, pie fillings

Cross-linked starch molecules
– Alter hydroxyl ends under alkaline conditions by
acetic anhydride, succinic anhydride, or ethylene
oxide
Viscosity and Cross-linked
Starches
Resistant Starch


Small intestine is unable to digest, limited digestion
in large intestine
Classifications
–
–
–
–
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RS1:
RS2:
RS3:
RS4:
trapped in cells (seeds/legumes)
native starch (raw potatoes, bananas, waxy maize)
crystalline, non-granular starch (cooked potatoes)
chemically modified
Can contribute fiber to food without the fat that
bran has
Takes up less water than other fiber, making dough
less sticky
Smooth even texture
Less than 3 cal/g