1. Megan Erickson Central Washington University
Starch
Megan Erickson
Central Washington University

2. What is it? Complex carbohydrate made up of two components Components:
Amylose
Amylopectin
Properties depend on amounts of the components

3. Where is it found? Roots/Tubers Cereal Potato Arrowroot Tapioca Corn
Waxy corn
Wheat
Rice
Waxy rice

4. Amylose Linear component of starch Contains 1,4-alpha-glucosidic bonds
Molecular weight: less than 0.5 million
Can form coils which will trap iodine and turn blue
Every 6 glucoses in the helix can bind one iodine. Test used to find percentage of amylose in starch

5. Amylopectin Branched component of starch
Contains 1,4-alpha-glucosidic as well as 1,6-alpha-glucosidic bonds
Molecular weight: million
Limited coiling causes purplish-red color when iodine added
Much larger in size than amylose
Purplish-red due to lack of helix.

6. Amylose vs. Amylopectin
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

7. Starch Composition

8. Starch Granule 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

9. Starch Granule
When looked at under polarized filters at right angles to each other, starch looks like birefringence pattern (maltese cross). When heated, pattern disappears.

10. Functions Gelatinization Dextrinization Gelation
Structure in baked products
Thickener in sauces, soups, and dressings
Dextrinization
Gelation
Pie filling

11. Gelatinization 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

12. 70 degrees, some imploding and some still swelling

13. Gelatinization and Temperature
Gradually thicken with temperature
Can be heated to 100oC without much granule rupture
If held at 95oC will implode and lose viscosity
Loses viscosity with prolonged heating

14. Gelatinization and Type of Starch
Best thickening ability: potato starch
Worst thickening ability: wheat starch
More amylopectin=more translucent=more stringy
Roots generally better thickeners than cereals because they have more amylopectin. Waxy starches better thickeners because lots amylopectin.
Flour is worse than wheat starch because of protein content.
Stringy is undesirable, smooth is desirable. This is why process tapioca into pearl tapioca so less stringy. Corn starch is good b/c not stringy, waxy cornstarch can be cross-linked so not stringy and translucent.

15. Viscosity and Type of Starch

16. Gelatinization and Sugar
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
Some cross-linking between starch and sugar also delays gelatinization.
Sugar increases translucence.

17. Gelatinization and Acid
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
Heat rapidly b/c lessens time the molecules can be hydrolyzed.
If add lemon juice after gelatinization need to remember that it is part of the liquid component and not bound to starch granules: may decrease viscosity.

18. Gelation 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
H-bonding can occur and break until gel is fully cooled.

19. 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
Waxy starches=high amylopectin=very soft gel.
Generally roots=good thickeners, cereals=strong gels=opaque gels due to protein content

20. 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
If temp. too high, will burst, if temp too low, limited amylose released.
If stir while heating too much, will break up granules and get weakened gel.

21. Gelation and Other Effects
Sugar
Decreases gelatinization and amylose release
Softer gel
Acid
Decreases gelatinization by hydrolysis of granules

22. Aging Gels Syneresis Retrogradation 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
Water is bonded to amylose and granules and free water is trapped, but not bonded, around the structure.
Syneresis happens due to aging and when cut a gel and water leaks out.
Retrogradation results in gritty texture. Heat breaks the H-bonds holding the amylose and lets them move within the gel.

23. Dextrinization When starch is heated without water
A higher temperature is reached than with water
Bonds break throughout the starch forming dextrins

24. 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
Problems with freezing and thawing are syneresis is pies. Not a problem in stews or other items that can be stirred so the water is recombined with the starch.
Edible films used in cough drops, candy, coatings for deep fried potatoes, produce, baked products

25. 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:
Measure molded gel height and compare to unmolded gel height
Stronger gel=small % sag, weaker gel=large % sag

26. Modified Starches 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
Poor processing to heat/shear/acid: due to granules bursting which decreases viscosity
Freeze/thaw: has to do with amylose binding

27. Pre-gelatinized Starches
Use:
Instant pudding
Dehydrated gelatinized starch
Heated so granule swells and then dehydrated
Swells when water added, no heat necessary
Decreases preparation time
Physical change

28. 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

29. Cross-linked Starch Use: Cross-linked starch molecules
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
Example of retrogradation is in refrigerated puddings. Amylose doesn’t realign b/c altered hydroxyl group doesn’t line up well.
Cross-links amylose

30. Viscosity and Cross-linked Starches

31. Resistant Starch
Small intestine is unable to digest, limited digestion in large intestine
Classifications
RS1: trapped in cells (seeds/legumes)
RS2: native starch (raw potatoes, bananas, waxy maize)
RS3: crystalline, non-granular starch (cooked potatoes)
RS4: 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