1. Carbohydrates
© PDST Home Economics

2. Photosynthesis
The process by which green plants use energy from the sun to change carbon dioxide and water into glucose and oxygen.
Carbon dioxide + Water → Glucose + Oxygen.
6CO H2O → C6H12O O2

3. Classification of Carbohydrates
There are 3 types of carbohydrates
Monosaccharides
Disaccharides
Polysaccharides

4. Monosaccharides- e.g glucose
CH2OH C H OH O C H OH H OH
C C H OH C

5. Monosaccharides A Monosaccharide contains one sugar unit
C6H12O6 is the chemical formula of a monosaccharide
Glucose, fructose and galactose are the 3 monosaccharides

6. Disaccharides
Are formed when two monosaccharides join together with the elimination of water (condensation)
There are three disaccharides: maltose, sucrose & lactose
The chemical formula is C12H22O11
C6H12O6
+C6H12O6
C12H24O12
- H2O
C12H22O11

7. Condensation reaction

8. Polysaccharides
These are formed when three or more monosaccharides join together with a loss of a water molecule each time.
They may be straight or branched
Examples: Starch, pectin, cellulose, gums & glycogen
Pectin, cellulose & gums are also known as Non-Starch Polysaccharides
Starch is made up of glucose units arranged as follows:
Straight chains are known as amylose or
Branched chains are known as amylopectin

9. Polysaccharides continued….
Formula: (C6H10O5)n
C6H12O6
H2O
(C6H10O5)n n=the number of times a bond is formed
Chemical structure of a polysaccharide

10. Classification of Carbohydrates
Chemical Formula
Example
Source
Monosaccharides
C6H12O6
Glucose
Fructose
Galactose
Fruit
Honey
Digested milk
Disaccharides
C12H22O11
Maltose=Glucose+Glucose
Sucrose=Glucose+Fructose
Lactose=Glucose+Galactose
Barley
Table sugar
Milk
Polysaccharides
(Complex Carbs)
(C6H10O5)n
Starch
Cellulose non-starch
Pectin poly-
Glycogen saccharides
Bread, pasta
Whole cereals
Fruit cell wall
Liver and muscle cells

11. Non-Starch Polysaccharides
These are also known as NSPs, dietary fibre and roughage
NSPs cannot be digested in the body and absorb large amounts of water
They aid the removal of waste from the body by a process known as peristalsis
Peristalsis is the muscular movement of food along the gut
Sources of NSPs include wholemeal bread, brown rice & wholemeal pasta
Refined foods contain few if any NSPs

12. Properties of Carbohydrates
Sugar
Starch
Non-Starch Polysaccharides

13. 1.Properties of Sugar 1.Solubility
Sugars are white crystalline compounds that are soluble in water
Solubility is increased by heating the water
A syrup is formed when sugar is heated
2. Assists Aeration
Sugar denatures egg protein, enabling aeration to occur, e.g. in the making of sponge cakes – the egg when whisked with sugar becomes aerated
3. Crystallisation
This occurs if more sugar is added than can be absorbed by a liquid
Crystal particles are formed when the mixture cools
Crystallisation is used in the confectionery and sweet industry

14. 1.Properties of Sugar cont….
4. Caramelisation
When sugars are heated, they produce a range of brown substances know as a caramel
There are ten gradual changes in sugar between melting and caramelisation
These stages occur between 104°C & 177°C
Eventually, the heat will cause carbonisation (burning)

15. 1.Properties of sugar cont….
5. Maillard Reaction
Sugar (Carbohydrate) + Amino Acid + Dry Heat = Browning of foods, e.g. roast potatoes
6. Sweetness
Sugar has varying degrees of sweetness based on a point scale using the tasting method
Sucrose has a relative sweetness of 100
Fructose has a relative sweetness of 170
Lactose has a relative sweetness of 15

16. 1.Properties of sugar cont….
7. Hydrolysis
Hydrolysis is the chemical breakdown of a molecule by adding water to produce smaller molecules
This occurs when water is added to a disaccharide to produce two monosaccharides
Hydrolysis is the reverse of the condensation reaction

17. 1.Properties of sugar cont….
8.Inversion
The hydrolysis of sucrose is also known as the inversion of sucrose (mixture of glucose & fructose), known as ‘invert sugar’
Inversion may be brought about by either: (a) heating sucrose with an acid; or (b) adding the enzyme invertase, or sucrase
Invert sugar is used in production of jam

18. 2. Properties of Starch Flavour
Starch (a white powder) is not sweet in flavour
2.Solubility
Starch is insoluble in cold water
Hygroscopic
This property relates to how starch absorbs moisture from the air e.g. biscuits soften if they are not kept air tight

19. 2. Properties of Starch 4. Dextrinisation
Dextrins are shorter chains of starch
On heating, dextrins form longer chains & become brown-coloured substances called pyrodextrins
An example of dextrinisation is toasting bread

20. 2. Properties of Starch cont…..
5. Gelatinisation is based on the principal that when starch is heated in the presence of water, starch grains swell, burst & absorb the liquid, resulting in the thickening of the liquid
As the temperature rises, this mixture becomes even more viscous, forming a sol (A sol contains particles that do not fully dissolve but are evenly dispersed throughout the liquid)
On cooling, this becomes a gel
An example of this is using flour to thicken soups and sauces

21. 2. Properties of Starch 6. Hydrolysis
Hydrolysis is a chemical breakdown of a molecule by adding water to produce smaller molecules
Disaccharides become monosaccharides partly due to hydrolysis

22. Properties of Non-Starch Polysaccharides
Cellulose
Can absorb large amounts of water
Cannot be digested, however adds bulk to the diet (gives a feeling of fullness)
Aids the removal of waste from the body
Is insoluble in water

23. 3. Properties of Non-Starch Polysaccharides
Pectin
Pectin is a polysaccharide found in fruit and vegetables
It is involved in setting jams & jellies
The following shows the pectin change in the ripening of fruit:
Under-Ripe to ripe to Over-Ripe
Protopectin to Pectin to Pectic Acid
(pectose)
For pectin extraction :
1. Use fruit rich in pectin, e.g. Blackcurrants & Apples
2. Heat needs to be applied to the fruit
3. Add an acid, e.g. Lemon juice changes protopectin to pectin

24. 3. Properties of Non-Starch Polysaccharides
3. Gel Formation
When pectin is heated in the presence of acid and sugar, water becomes trapped
The long chains of polysaccharides cool to form a gel
An example of this is in making jam

25. Effects of Heat on Carbohydrates
Dry Heat
Moist Heat
Carbohydrate foods browns due to the presence of dextrins, e.g.Toast
Sugar caramelises, e.g. Caramel slices
Maillard reaction occurs because of the interaction between sugar & amino acids, e.g. roast potatoes
Cellulose softens, e.g. cooked vegetables
Starch grains swell, burst & absorb liquid, e.g. flour used to thicken sauces
Pectin is extracted by heating fruit in water with sugar & acid, e.g. jam making
Sugar dissolves in warm liquid, e.g. making syrups

26. Culinary uses of sugar Sweetener - desserts Preservative - jam
Caramelisation – caramel custard
Fermentation – yeast bread
Gel formation – sugar combines with pectin to form gel – jam making.
Colour – a sugar solution prevents discolouration of cut fruit.

27. Culinary uses of starch
Thickener – sauces, soups, stews.
Hygroscopic – absorbs moisture to increase shelf life of cakes, keeps baking powder dry.
Dextrinisation – browning e.g.toast.

28. Culinary uses of non-starch polysaccharides
Gel formation – jam pectin forms gel with acid and sugar.
Cellulose absorbs moisture and gives feeling of fullness.
Cellulose adds texture e.g. breakfast cereals

29. Biological Functions of Carbohydrates
Carbohydrates are used for heat and energy for the body.
They spare protein so it can be used for growth and repair.
Excess carbohydrate is changed to glycogen and stored in liver and muscle as an energy reserve or it is changed to body fat (adipose tissue) which insulates the body.
Cellulose moves food through intestine preventing constipation.

30. Digestion of Carbohydrates
Mouth: Physically broken by teeth.
Salivary Amylase breaks Starch into Maltose.
Stomach: Physically churned up.
Intestine: Pancreatic juice Amylase breaks Starch into Maltose.
Intestinal Juice: Maltase breaks Maltose into Glucose.
Sucrase breaks
Sucrose into Glucose & Fructose.
Lactase breaks
Lactose into Glucose and Galactose.

31. Absorption Absorption:
Monosaccharides are absorbed through the villi of the small intestine into the blood stream and are carried to the liver in the portal vein.

32. Assimilation of Carbohydrates
Monosaccharides can be oxidised to produce energy (cellular respiration).
Some monosaccharides are changed to glycogen and stored in liver and muscle as an energy reserve.
Excess carbohydrate is changed to body fat and stored in the adipose tissue under the skin.
Vitamin B1, B2 and Pyrodoxine are needed to metabolise carbohydrates.

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