topic7 starch

Question 1

what is starch?

Answer 1

A carbohydrate, It is a polysaccharide made up of glucose molecules

Question 2

2 major categories of starch?

Answer 2

Native Starch
Modified Starch

Question 3

what is native starch?

Answer 3

pure starch isolated from original plant material

Question 4

what is modified starch?

Answer 4

native starch that has undergone chemical or physical processing to change its properties

Question 5

2 structures of starch

Answer 5

amylose 直链淀粉
amylopectin支链淀粉

Question 6

how to distinguish amylose and amylopectin

Answer 6

Amylose bule
Amylopectin red purple

Question 7

amylose is responsible for gelling or thickening?

Answer 7

gelling

Question 8

amylopectin is responsible for gelling or thickening?

Answer 8

thickening

Question 9

what is waxy variety?

Answer 9

only contains amylopectins

Question 10

sources for starch

Answer 10

Cereal grains (corn, wheat, rice, oats)
Legumes (dried beans)
Roots and tubers (potato, tapioca, arrowroot)

Question 11

basic ingredients for bubble tea?

Answer 11

black tea, water, tapioca pearls, milk, syrup or sweetener

Question 12

why is the tapioca pearls have a dark appearance?

Answer 12

added brown sugar or caramal

Question 13

wet milling process

Answer 13

1. Cleaning
2. Grinding or Grating
3. Slurry
4. Separation/Refining
5. Drying

Question 14

maize starch = corn starch

Question 15

what’s the difference between whole grain and the white grain

Answer 15

no germ(for oil), no bran(for fibre)， so has a little nutritive value

Question 16

what’s the use of refined starch?(white grain)

Answer 16

Added to other foods to act as a thickener增稠剂, stabilizer稳定剂, bulking agent膨松剂 and anticaking agent抗结剂()

Question 17

Terminology
Gel and colloid(sol)

Answer 17

Gel:colloidal dispersion that holds shape保持形状的胶体分散物
Sol:intermediate between small particles in solution and large particles in suspension介于溶液中的小颗粒和悬浮液中的大颗粒之间

Question 18

Starch is deposited in plants in organized units called granules

Answer 18

in Seeds, roots and tubers

Question 19

Birefringence of starch

Answer 19

When the starch molecules are observed microscopically under polarized light当在偏振光下显微镜观察淀粉分子时Light is rotated so that the cross-pattern on each granule is observed,光被旋转，以便观察到每个颗粒上的交叉图案This pattern disappears once the starch is heated一旦淀粉被加热，这种图案就会消失

Question 20

what is native starch

Answer 20

Developed through traditional plant breeding or genetic engineering No physical or chemical modification of the starch

Question 21

what is modified starch?

Answer 21

Chemical or physical modifications may be used to change function in food preparation

Question 22

how to modify starch?

Answer 22

1. Hydrolysis or acid-converted–>used in the confectionary糖果，甜食
2. Cross-linked or cross-bonded:improved viscosity and texture
3. Substitution or stabilization prevents retrogradation凝沉

Question 23

the use of hydrolysis or acid converted starch

Answer 23

produces Low viscosity paste, stiff gel, Useful in confectionary industry

Question 24

the use of cross linked or cross bonded starch

Answer 24

Increased temperature for hydration therefore greater tolerance to heat, Resistant to shear or stirring,Useful for canned soup, spaghetti sauces, and pie fillings

Question 25

steps of hydrolysis starch

Answer 25

1. mix starch with water 2.add acid 3. dry

Question 26

steps for physically modified starch

Answer 26

1.Instant or pregelatinized --> instant dry mixes, gravies, sauces 2. Cold-water swelling --> pregelatinized\ 3. Heat treated ---> greater viscosity and stability

Question 27

what is resistant starch

Answer 27

Resistant starch is not digested by the human body

Question 28

4 main types of resistant starch

Answer 28

RS1 resistant to digestion ex whole grains, seeds RS2 resists digestion due to compact structure ex green bananas RS3 retrograded ex cooked and cooled potatoes RS4 only one chemically modified ex modified starches

Question 29

dry heat and starch

Answer 29

Starch becomes more soluble Reduced thickening ability Dextrinization -->when starch is broken down into dextrins糊精化——淀粉被分解成糊精 Brown, nutty, toasted flavor develops

Question 30

examples of the use of dry heated starch

Answer 30

Examples: Brown Roux and Espagnole Sauce

Question 31

moist heat and and starch

Answer 31

Starch granules insoluble in cold water so Colloidal dispersion produced with heating produces Starch paste

Question 32

Changes with Moist Heat and Cooling

Answer 32

Gelatinization凝胶化:With heat, starch granules absorb water and swell Pasting浆糊 Gel formation or gelation -->during cooling Retrogradation

Question 33

when would retrogradation happen?

Answer 33

Occurs upon standing after gel formation

Question 34

what is retrogradation like?

Answer 34

Amylose molecules associate more closely, the gel netnork syneresis(脱水缩合)

Question 35

Factors Affecting Starch Pastes

Answer 35

1. Temperature and time of heating 2. Agitation and stirring 3. Acidity 4. Addition of other ingredients

Question 36

Temperature and Time of Heating ---> starch pastes

Answer 36

Thicker if cooked quickly undercooked pastes will have a raw starch flavour, and less smooth and silky

Question 37

Agitation or Stirring and starch pastes

Answer 37

Stirring is desirable to disperse starch,If excessive – starch granules may rupture破裂 and develop a Slick and pasty mouthfeel口感柔滑，糊状

Question 38

Acidity (pH) and starch pastes:Add acid late in cooking process(lemon pie)

Answer 38

May cause fragmentation and hydrolysis,pH below 4 will lead to a thinning of paste cross-linked starch has a better resistance of acid

Question 39

Addition of Other Ingredients and starch pastes

Answer 39

Sugar Raises temperature of gelatinization,May decrease viscosity Fats and proteins Delay hydration of starch Lowers rate of viscosity development

Question 40

Starch Cookery:Combining starch with hot liquids

Answer 40

Roux: prepared by blending melted fat with flour Slurry: mixing flour or starch with some of the cold liquid which is then added to a hot liquid while stirring

Question 41

how to thickening a liquid with a roux?

Answer 41

(a) add cold liquid or stock to a hot roux or (b) add cold roux to a hot liquid or stock.

Question 42

why not recommend to blend a hot roux into hot liquid?

Answer 42

it is very difficult to smoothly blend the roux into the liquid before lumps are formed due to the rapid gelatinization of the starch. 由于淀粉的快速糊化，在形成团块之前，将面粉糊顺利地混入液体是非常困难的。

Question 43

Five Basic Mother Sauces

Answer 43

1. Bechamel 白酱with milk 2. Veloute 白酱with chicken stock 3. Espagnole 红酱with beacon 4. Tomato 5. Hollandaise 蛋黄酱

Question 44

sauce that thickened by starch

Answer 44

1. Bechamel (white sauce) --->fat, flour, milk, seasonings 2. Veloute ---> fat, flour, veal/chicken/fish stock, seasonings 3. Espagnole ---> fat, flour, beef stock, seasonings

Question 45

sauce that May be thickened with starch

Answer 45

tomato