2.2.functional properties of carbohydrates in food

Question 1

What are the 3 groups of carbohydrates?

Answer 1

monosaccharides, disaccharides and polysaccharides.

Question 2

What are monosaccharides, give examples?
+structure

Answer 2

singer sugar molecules eg.Glucose - fruits, fruit juices, honey
Fructose - fruits and honey
Galactose - milk
-structure on fc

Question 3

What are disaccharides, give examples?
+structure

Answer 3

-2 monosaccharides joined by a glycosidic link
eg.Sucrose - sugar cane, sugar beet
Lactose - milk
Maltose- cereals such as barley
-structure on fc

Question 4

What are polysaccharides, give examples?

Answer 4

-Many monosacharides joined by a glycosidic link
Starch - wheat flour, corn flour, potatoes
Pectin - fruits
Cellulose - fruits and vegetables
Glycogen

Question 5

What happens when starch is subjected to dry heat?

Answer 5

-dextrinisation- a form of enzymic browning:
undergoes a partial chemical breakdown into shorter glucose chains called dextrins.:
starch(polysaccharide) -> dextrins -> maltose (disaccharide) -> glucose (monosaccharide)

Question 6

Examples of dextrinisation of starch?

Answer 6

Bread which is toasted
Baked cakes and biscuits
Toasted breakfast cereals
Gravy being brown
A brown crust on baked vegetables such as potatoes

Question 7

What effect does dextrinisation have on the sensory properties of food?

Answer 7

causes change in colour, aroma and flavour

Question 8

What different characteristics does dextrin have to starch?

Answer 8

-Dextrin will dissolve in cold water, starch does not.
-Dextrin has a sweet taste, starch has a floury taste.
-Dextrins are not good at thickening, starch gelatinizes and thickens foods such as sauces.

Question 9

Factors affecting the amount of dextrinisation?

Answer 9

The length of time that starch is exposed to dry heat
The temperature of the dry heat
The type of starch
The action of acids
The action of enzymes

Question 10

What can starch be found in?

Answer 10

grains like rice and wheat, as well as vegetables such as potatoes and cassava.

Question 11

What are starch molecules made up?

Answer 11

amylose- unbranched chains of glucose and amylopectin- branched chains of glucose

Question 12

What affect does the ratio of amylose to amylopectin have on food?

Answer 12

determines the thickness of the gel produced.
-high amylose starches are used when a rigid gel is needed because they aid gelling due to spiral shape and form a network where water is trapped
-amylopectin molecules are larger but more compact so don’t hold water as well

Question 13

Examples of starch content in foods?

Answer 13

Potato starch:
24% amylose 76% amylopectin
Tapioca starch 13% 87%
Rice starch: 15%. 85%

Question 14

What is gelatinisation?

Answer 14

occurs when starch granules are heated in a liquid, causing them to swell and burst, which results in the liquid thickening.

Question 15

Factors affecting gelatinisation of starch?

Answer 15

Temperature
Agitation
The pH
The addition of other ingredients

Question 16

How does temperature affect the gelatinisation of starch?

Answer 16

-at 64 to 72℃ the outer layer of the starch grain swells allowing it to gradually swell with water.
-At 86 to 90℃ the starch grains burst and release amylose and amylopectin that thicken the liquid and form a gel.
- Gelatinisation of all the starch should occur if the mixture is boiled for at least one minute.
-A roux to make a sauce involves heating starch with butter to starch to soften the starch and also produce dextrins.

Question 16

How does agitation affect the gelatinisation of starch?

Answer 16

-to create a smooth sauce within the temperature range within which starch is gelatinized, the mixture should be stirred.
-Cold water should be added to a starch mixture, rather than adding a starch to a hot liquid.
-Lumps will occur if starch is added to a hot liquid because some of the starch will immediately starch to gelatinise.

Question 17

How does the addition of acids affect the gelatinisation of starch?

Answer 17

-vinegar, lemon juice and other fruit juices breakdown the starch molecules into smaller molecules of dextrin which do not thicken so effectively.
-Therefore acids may be added once gelatinisation has taken place.

Question 18

How does the addition of sugar affect the gelatinisation of starch?

Answer 18

-sugar competes with the starch for water and also raises the temperature at which starch starts to gelatinise.

Question 19

How does the addition of fat affect the gelatinisation of starch?

Answer 19

a equal mixture of fat and starch in a roux helps to disperse the starch and prevent lumps forming in a sauce.

Question 20

What are the 2 methods of sauce making?

Answer 20

-all in one method:
all ingredients and cold liquid are mixed together in a pan then brought to the boil. Stirring or whisking is required all the time to prevent the sauce from going lumpy.
-roux method:
consists of equal quantities of butter and plain flour. The fat is melted, the flour is mixed through over a gentle heat. Hot liquid is then gradually mixed into the paste to make a silky sauce

Question 21

what is the crystallisation of sugar?

Answer 21

(sucrose) its ability to dissolve and reform crystals.

Question 22

what is the function of crystallising sugar?

Answer 22

used to make confectionary such as caramel, fudge and toffee.

Question 23

describe the process of sugar crystallisation?

Answer 23

-When sugar is dissolved and heated to a liquid, the liquid evaporates and creates a more saturated (or supersaturated) sugar solution.
-As the sugar solution cool, the sugar forms into crystals. -If the solution is not stirred and cools quickly, the crystals will be very small and the texture will be smooth.

Question 24

what factors affect the functional properties of sugar?

Answer 24

Temperature
Agitation
The pH
The addition of other ingredients

Question 25

How does temperature affect sugar?

Answer 25

-the solidity of caramel or toffee is affected by the temperature and time the solution is heated.
-Water that is hotter can dissolve more sugar to create more crystals and so a more solid product.
-The solidity of a product is also affected by the amount of time it is heated, as the longer the liquid is heated the more it will dissolve and create a more concentrated sugar solution

Question 26

what temperature should fudge, soft caramel and hard caramel be heated too?

Answer 26

fudge-112 - 116℃
soft caramel-118 - 121℃
hard caramel-121 -130℃

Question 27

how does pH affect the crystallisation of sugar?

Answer 27

-acidity will help create “invert sugar”. This is when lemon juice or cream of tartar splits the bond joining the disaccharide sucrose together forming separate monosaccharides glucose and fructose.
- invert sugar is sweeter and tends to be less prone to crystallization and retains moisture. This gives confectionary a smooth texture.

Question 28

how does agitation affect the crystallisation of sugar?

Answer 28

-stirring a sugar solution encourages the development of crystals.
- it is important that sugar is stirred and dissolved before it boils when ,making confectionary or the mixture will crystallize and have a grainy texture.
-Stirring (or agitation) impacts on the texture and accounts for the difference between fudge and caramel

Question 29

how does the addition of other ingredients affect the crystallisation of sugar?

Answer 29

fat or cream surrounds small sugar crystals and prevents large crystals forming.

Question 30

what happens during the caramelisation of sugar?

Answer 30

Sucrose melts at 186℃ and the molten sugar changes colour to a light brown and caramelised as acid and glucose form. The longer it is heated the darker it becomes.

sucrose + heat ->. glucose +fructose +water ->
acids + glucose

Question 31

What factors affect the amount of caramelisation?

Answer 31

The quantity of sugar
The length of time and the temperature of heated
The type of sugar
The addition of other ingredients

Question 32

Uses of caramelisation?

Answer 32

-baked products such as cakes and biscuits.
-often used as a colouring in commercially made flavoured milk, cakes, breakfast cereals and ice-cream.

Question 33

Where’s pectin found and what is it used for?

Answer 33

found in many fruits and is used to create gels, such as jams and jellies.
eg. Lemons and limes
Apples
Blackberries, cranberries and grapes
Guavas and sour plums

Question 34

what happens to fruit with a moderate pectin content?

Answer 34

the addition of an acid or commercially made pectin concentrate is required
-The more ripe a fruit is, the less pectin it contains.

Question 35

How is jam made using pectin in fruit?

Answer 35

-fruit containing pectin is boiled with sugar to create a gel.
-At 105℃ the mixture should create a gel on cooling.
This can be checked by spooning a little jam onto a cold plate and after leaving it for 30 seconds it should wrinkle when pushed

Question 36

What is the impact of acid on pectin gelation?

Answer 36

-addition of acid increases gel formation
-The more acid added, the stronger the gel is formed and the higher the water binding ability. Gel formation can only occur in a narrow pH range of 3.1 to 3.5.

Question 37

affect of the addition of sugar on starch?

Answer 37

-sugar competes with starch for water therefore reducing gel strength

Question 38

affect of the addition of acid on starch?

Answer 38

-acid hydrolyses starch and reduces gel strength forming a viscous paste eg. occurs in a lemon pie filling