Carbohydrates

• 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.