Carbohydrates Notes PDF

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. 6CO2 + 6H2O → C6H12O6 + 6O2 Classification of Carbohydrates There are 3 types of carbo...

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. 6CO2 + 6H2O → C6H12O6 + 6O2 Classification of Carbohydrates There are 3 types of carbohydrates 1. Monosaccharides 2. Disaccharides 3. Polysaccharides Monosaccharides- e.g glucose CH2OH C O H H H C C OH H OH OH C C H OH Monosaccharides A Monosaccharide contains one sugar unit C6H12O6 is the chemical formula of a monosaccharide Glucose, fructose and galactose are the 3 monosaccharides 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 Condensation reaction 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: 1.Straight chains are known as amylose or 2.Branched chains are known as amylopectin Polysaccharides continued…. Formula: (C6H10O5)n C6H12O6 --- H2O (C6H10O5)n n=the number of times a bond is formed  Classification of Carbohydrates Class Chemical Example Source Formula Monosaccharides C6H12O6 Glucose Fruit Fructose Honey Galactose Digested milk Disaccharides C12H22O11 Maltose=Glucose+Glucose Barley Sucrose=Glucose+Fructose Table sugar Lactose=Glucose+Galactose Milk Polysaccharides (C6H10O5)n Starch Bread, pasta (Complex Carbs) Cellulose non-starch Whole cereals Pectin polysaccharides Fruit cell wall Glycogen Liver and muscle cells 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 Properties of Carbohydrates 1. Sugar 2. Starch 3. Non-Starch Polysaccharides Properties of Sugar 1. Solubility  Sugars is a white crystalline compound.  Sugar is water soluble.  A syrup is formed when a large amount of sugar is dissolved in a small amount of water. Culinary application: Used as a preservative in canned fruit, e.g. canned peaches Did you know? When food is canned in a high sugar solution, the sugar draws water from bacterial cells by osmosis. Without water bacteria cannot grow, and so the food is preserved. Properties of Sugar 2. Flavour/Sweetness  All sugars are sweet and give an appetising flavour to food.  Some sugars are much sweeter than others.  This is measured on a point scale of sweetness.  E.g. Sucrose has a relative sweetness of 100%, Fructose has a relative sweetness of 170% however glucose has a relative sweetness of 75% and lactose has a relative sweetness of 15%. Culinary application: Shortbread, cupcakes Properties of Sugar 3. Assists aeration  Aeration occurs when sugar is whisked with egg whites.  The sugar helps denature the egg protein, causing it to unfold and entrap air bubbles.  Whisking also creates heat that begins to set the egg albumin.  This forms a temporary foam, which will collapse after a while unless it is heated to coagulate and set a permanent foam. Culinary application: meringues, sponges– the egg when whisked with sugar becomes aerated Properties of Sugar 4. Maillard reaction  The maillard reaction is a non-enzymic browning of food due to a reaction between certain amino acids and sugars under dry heat.  It produces an attractive brown colour and a crust with an appetising flavour.  Sugar (Carbohydrate) + Amino Acid + Dry Heat = Browning of foods, e.g. roast potatoes  Occurs on heating and causes browning Culinary application: Shortbread biscuits, roast potatoes, roast meat Properties of Sugar 5. Caramelisation  When sugar is heated it melts, and then caramelises i.e. changes to a brown syrup (Caramel).  This occurs over 10 gradual stages between melting and caramelisation (Stages between 104°C and 177°C).  Caramelisation normally occurs at 160⁰C, resulting in an attractive brown colour and a sweet taste.  If overheated (above 177⁰C), carmel will carbonise or burn. Culinary application: Crème caramel, carmel squares https://www.bbcgoodfood.com/videos/techniques/how-make-caramel-video Properties of Sugar 6. Crystallisation  When a liquid has dissolved as much sugar as it can, it is saturated.  If more sugar is added, crystals of sugar form in the solution and solidify when cooled. Culinary application: confectionery and sweet- making e.g. fudge. Properties of Sugar 7. Hydrolysis  Hydrolysis (the reverse of condensation) occurs during digestion.  This is the chemical breakdown of a molecule by adding water to produce smaller molecules.  Sugars (disaccharides) react with water and enzymes which breaks down the sugar to two monosaccharides units e.g. lactose into glucose and galactose. Properties of Sugar 8. Inversion  Inversion occurs when a liquid sucrose solution is heated in the presence of an acid or enzyme, causing the sucrose (disaccharide) to spilt into glucose and fructose (monosaccharide).  This is known as an invert sugar, and it is sweeter than sucrose. Culinary application: Jam-making. Inversion results in a smooth jam, as invert sugars dissolve easily, preventing sugar crystals from forming. Caramelisation Assists Aeration Crystallisation Hydrolysis LACTASE LACTOSE GLUCOSE GALACTOSE Solubility Maillard Reaction Inversion Sweetness 2. Properties of Starch 1. Flavour ❖ Starch (a white powder) is not sweet in flavour 2.Solubility ❖ Starch is insoluble in cold water 3. Hygroscopic ❖ This property relates to how starch absorbs moisture from the air e.g. biscuits soften if they are not kept air tight 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 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 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 Dietary Fibre/Cellulose Cellulose/ Dietary Fibre is insoluble in water. It cannot be digested by the body, however adds bulk to the diet (gives a feeling of fullness). It absorbs water as it passes through the intestinal tract and it stimulates the removal of waste from the body by a process known as peristalsis. Peristalsis is the muscular wave-like movement caused by the muscles of the large intestine contracting and relaxing. This is beneficial to the body as it speeds up the passage of food and waste, preventing bowel disorders, e.g. constipation. To Increase Fibre Intake: Reduce intake of sugar and refined starch. Include wholegrains in the diet  Choose brown bread, pasta and rice Add bran, seeds and nuts Increase intake of fruit and vegetables  Gums Gums are soluble in water. They have the ability to absorb large amounts of water to form a thick gel with a firm texture. Culinary application: Salad dressings, ice cream. What Is Xanthan Gum And Why Is It In Everything – YouTube  Properties of Pectin Pectin is a naturally present in plant cell and the cell walls of fruit and vegetables. It is used as a setting agents in jams and jellies, as it has the ability to absorb water to form a gel. It is only present in fruits when they are ripe. In under ripe fruits it is the form of protopectin, and in overripe fruits it becomes pectic acid, neither of which can set as they cannot absorb water. For pectin to be extracted it needs heat and acid, e.g. lemon juice Culinary application: Jam-making 3. Properties of Non-Starch Polysaccharides 2. 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 PROPERTIES OF NON- STARCH POLYSACCHARIDES Effects of Heat on Carbohydrates Dry Heat Moist Heat ▪ Carbohydrate foods ▪ Cellulose softens, e.g. browns due to the cooked vegetables presence of ▪ Starch grains swell, dextrins, e.g.Toast burst & absorb liquid, ▪ Sugar caramelises, e.g. flour used to e.g. Caramel slices thicken sauces ▪ Maillard reaction ▪ Pectin is extracted by occurs because of heating fruit in water the interaction with sugar & acid, e.g. between sugar & jam making amino acids, e.g. ▪ Sugar dissolves in roast potatoes warm liquid, e.g. making syrups  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. 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.  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  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.  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. 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.  Utilisation of Carbohydrates ❑ Monosaccharides can be oxidised to produce heat and 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.  Questions 1. List the three elements found in carbohydrates. (6) 2007 OL 2. Give an account of carbohydrates under each of the following headings: Classification Dietary sources. (18) 2019 OL 3. Classify carbohydrates. With reference to each class give: The chemical formula Examples Food source. (15) 2017 HL Questions 4. Give an account of carbohydrates under the following heading: properties. (4) 2014 OL 5. Explain three properties of sugar and the related culinary use of each. (15) 2017 HL. 6. In relation to carbohydrates, explain each of the following properties: Carmelisation Crystallisation (6) 2014 HL Questions 7. Describe the effect of gelatinisation on starch. Give two culinary examples of gelatinisation. (6) 2017 HL. 8. In relation to carbohydrate, explain the property dextrinization. (6) 2009 HL. 9. Name and explain three properties of carbohydrates that are useful in food preparation. (18) 2005 HL. 10. State two effects of heat on starch. (6) 2009 OL. 11. Give an account of carbohydrates under the heading: functions in the body (8) 2019 OL.  Questions 12. Identify three health problems that are caused by a diet high in sugar. (6) 2018 OL. 13. Assess the effects of high sugar consumption on the body. (10) 2017 OL. 14. Complete the following statement in relation to the biological function of carbohydrates using the following words: Liver Energy Cellulose Glucose releases heat and _____________. Excess glucose is stored as energy in the ________ and muscles. __________ stimulates the movement of food through the bowel. (6) 2010 OL.  Questions 15. Name a digestive enzyme that converts starch to maltose. (2) 2005 OL. 16. Complete the table below in relation to the digestion of carbohydrates. (6) 2018 HL. Organ Enzyme Substrate Product Pancreas Small Intestine