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Carbohydrates

Carbohydrates. 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 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2. Classification of Carbohydrates.

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Carbohydrates

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  1. Carbohydrates

  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. • 6CO2 + 6H2O → C6H12O6 + 6O2

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

  4. Monosaccharides- e.g glucose CH2OH C H OH H 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 mono saccharides 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

  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 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 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

  14. 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

  15. 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)

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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

  26. Effects of Heat on Carbohydrates • 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 Dry Heat Moist Heat

  27. 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.

  28. 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.

  29. 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

  30. 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.

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

  32. 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.

  33. Utilasationation 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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