EXAM 4: Starches And Starch Transformations

Question 1

Where are starches stored?

Answer 1

They are stored within the amyloplasts of plants

Question 2

What is the storage form of starch in the granules

Answer 2

Amylose and Amylopectin

Question 3

What are the uses of plant sources of starch

Answer 3

Gelling
Thickening
Binding
Moisture retention
Stabilizing
Anti-staling

Question 4

What is the use of plant sources of starch in gluten free products

Answer 4

Improves baking characteristics
- volume, color, crumb structure and texture

Question 5

What are examples of plant sources of starch

Answer 5

Cereal grains, roots and tubers, legumes

Question 6

How do plant sources of starch differ?

Answer 6

Their Amylose:Amylopectin ratio

Question 7

What are examples of grain starches

Answer 7

Wheat flour
Cornstarch
Rice

Question 8

What is the amylose:amylopectin ratio of wheat flour

Answer 8

28%:72%

Question 9

What is the amylose:amylopectin ratio of cornstarch

Answer 9

28%:72%

Question 10

What are examples of root starches

Answer 10

Potato starch
Tapioca
Arrowroot

Question 11

What is the amylose:amylopectin ratio of potato starch

Answer 11

21%:79%

Question 12

What is the amylose:amylopectin ratio of tapioca

Answer 12

18% to 83%

Question 13

What is the amylose:amylopectin ratio of arrowroot

Answer 13

17% to 21%

Question 14

What are examples of waxy starches

Answer 14

Waxy hybrid - corn, sorghum, potato

Question 15

What is the amylose:amylopectin ratio of waxy hybrid

Answer 15

0% to 100%

Question 16

What is the granule size of potato

Answer 16

It has the largest granule size

Question 17

What is the granule size of wheat and corn

Answer 17

Medium granule size

Question 18

What is the granule size of tapioca

Answer 18

Small to medium granule size

Question 19

What are the two commercial uses of starches

Answer 19

Modified starches and resistant starches

Question 20

What are modified starches

Answer 20

Chemical or physical modifications may be used to change function in food preparation
- hydrolysis or acid-converted
- cross-linked or cross-bonded
- substitution or stabilization
- physically modified
- instant or pregelatinized
- cold-water swelling
- heat treated

Question 21

What are resistant starches

Answer 21

They are not digested by humans
Used in foods to increase fiber content

Question 22

What are types of starch transformations

Answer 22

• Dextrinization
• Gelatinization (sol)
• Gelation (gel)
• Retrogradation & Syneresis

Question 23

What is dextrinization

Answer 23

The breakdown of amylopectin molecules to smaller glucose molecules known as “dextrins”, which are produced by dry heat (toasting or roasting)

Question 24

What is Gelatinization (sol phase)

Answer 24

The increase in volume, viscosity and translucency of starch granules in a liquid

Question 25

Amylose is a _________ ________ structure which means it is _________ likely to intertwine with starch molecules

Answer 25

Linear chain, more

Question 26

Amylopectin is a _________ ____________ structure, so it is ________ likely to intertwine with starch molecules

Answer 26

Branched chain, less

Question 27

What temperature does gelatinization start

Answer 27

140 degrees Gelatinization occurs with heat

Question 28

What are factors that affect gelatinization

Answer 28

Temperature and time of heating Acidity Agitation or stirring Additional of other ingredients

Question 29

How does temperature and time of heating affect gelatinization

Answer 29

Thicker if cooked quickly If undercooked - raw starch flavor - less smooth and silky Prolonged heating reduces gel strength

Question 30

How does Acidity (pH) affect gelatinization

Answer 30

PH < 4 causes fragmentation and hydrolysis Decreases thickening power Add acid late in cooking process

Question 31

How does agitation or stirring affect gelatinization

Answer 31

Gentle stirring desirable to disperse starch Whisk can be used to lessen lumps but it should be gentle If excessive - starch granules may rupture

Question 32

How does the addition of other ingredients affect gelatinization

Answer 32

Sugar - raises the temperature of gelatinization - may decrease viscosity - sucrose > lactose > glucose > fructose Fats - delays starch hydration - lowers rate of viscosity development Salt - increases gel strength

Question 33

What is the general process of gelation (gel)

Answer 33

Mix starch and liquid, then cool until a gel is formed Water is dispersed within the amylose

Question 34

What happens after the gel is cooled further?

Answer 34

Retrogradation

Question 35

What is retrogradation

Answer 35

- increase hydrogen bonding among amylose molecules as starch-water mixture cools, esp. in the refrigerator - creates gumminess and the staling of bread

Question 36

What is syneresis

Answer 36

The loss of liquid from a gel

Question 37

Why does starch type make a difference

Answer 37

Starch thickens at different rates

Question 38

What is the amount of potato starch needed to achieve designated thickness at 203 degrees F

Answer 38

1.96

Question 39

What is the amount of tapioca starch needed to achieve designated thickness at 203 degrees F

Answer 39

3.54

Question 40

What is the amount of arrowroot starch needed to achieve designated thickness at 203 degrees F

Answer 40

4.37

Question 41

What is the amount of corn starch needed to achieve designated thickness at 203 degrees F

Answer 41

5.48

Question 42

What is the amount of wheat flour needed to achieve designated thickness at 203 degrees F

Answer 42

9.27

Question 43

What are some qualities of root and tuber starches

Answer 43

More effective as thickening agents vs. cereal starches Thicken faster at a lower temp Less time needed to impart the same thickening properties as wheat flour

Question 44

Should you use higher or lower amounts of wheat flour vs corn starch or starches from roots and tubers to thicken a paste or create a gel

Answer 44

Higher

Question 45

If substituting corn starch, potato starch, arrowroot starch, etc. for wheat flour would you increase or decrease the amount used

Answer 45

Decrease

Question 46

Look at starch types and characteristics handout

Question 47

What are factors that lead to a sauce that breaks or “thins” the sauce

Answer 47

Heat too long after the sauce is at peak thickening Boil the sauce for too long Vigorous stirring

Question 48

Look over starches table