Carbohydrates

Cards (21)

  • The chemicals that make up carbohydrates are: Oxygen (O), Hydrogen (H) and Carbon (C).
  • The general formula for carbohydrates is C6H12O6.
  • Photosynthesis: is where green plants make carbohydrates using water from the soil and carbon dioxide from the air to provide the carbon, hydrogen and oxygen.
  • Simple carbohydrates are known as sugars. Sugars are crystalline substances that dissolve in water at different temperatures and also vary in sweetness. 
  • There are two different groups of sugars: Monosaccharides and disaccharides.
  • Monosaccharides
    Glucose = Found in ripe fruits and some vegetables (e.g. onions).
    Glucose forms a Hexose ring.
    Fructose = Fruit sugar, (found in fruits plant juices and honey).
    Fructose makes a Pentose ring.
    Galactose = Only found in mammalian breast milk.
    Galactose makes a Hexose Ring.
  • Disaccharides are formed during condensation reactions. As a result of this a glycosidic bond/link is formed between the two monosaccharides, with the loss of a water molecule. They are double sugars. They form when two monosaccharides join together.
    • Sucrose = formed from one molecule of glucose and one molecule of fructose. (sucrose is the main sugar used in cooking).
    • Lactose = ‘Milk sugar’, formed from one molecule of glucose and one molecule of galactose. 
    • Maltose = ‘malt sugar’, formed from two molecules of glucose. 
  • Polysaccharides are large molecules made up of mostly glucose.
  • Polysaccharides are not sweet as they are too big to produce a response from the taste buds on the tongue.
  • Polysaccharides are formed by green plants and used as a store of energy in roots, tubers and seeds.
  • Polysaccharides give shape to the stems, shoots, leaves and seeds.
  • Starch is a polysaccharide with many glucose molecules stored in microscopic granules in plants.
  • Starch is made up of Amylose (20-25%) and Amylopectin (70-80%).
  • Dextrin is a polysaccharide formed with starchy foods during baking or toasting, known as DEXTRINISATION, which gives colour and flavour.
  • Cellulose is a polysaccharide that humans cannot digest, making it insoluble dietary fibre.
  • Cellulose is arranged in straight lines and gives plants their structure to grow tall.
  • Some animals such as cattle, sheep and rabbits can digest cellulose as they produce the enzyme CELLULASE.
  • Pectin is a polysaccharide that forms a gel with water to help jams set.
    • Sources of Monosaccharides = Honey, dried fruits such as apples or canned fruits such as pineapple.
    • Sources of Disaccharides = Table sugar, cakes, beetroot and carrots.
    • Sources of Polysaccharides = Grains, vegetables, fruits, nuts and cereal bran.
  • Digestion of Carbohydrates
    • Salivary amylase begins digestion in the mouth.
    • Salivary amylase is denatured by stomach acids.
    • Pancreatic amylase continues digestion in the small intestine.
    • Enzymes at the microvilli break down carbohydrates into monosaccharides.
    • Resistant starches and fibers are digested and fermented in the large intestine and the colon.