Microorganisms

• Yeast is a single celled fungi. Some are useful in baking and brewing, others can be pathogenic
• Making bread:

  • Mix flour with warm water and yeast
  • Add salt, sugar and a little oil
  • Knead the dough for 5 minutes
  • Prove the dough for two hours at 25 degrees
  • Knead and shape the dough
  • Prove for another hour at 25 degrees
  • Bake at 230 degrees for 15 minutes
  • Allow to cool before eating
• The purpose of mixing the ingredients is so all the reactants are evenly distributed
• The dough is kneaded by stretching and folding the dough to incorporate air and activate the yeast
• The yeast producing CO2 as a product of anaerobic respiration produces air bubbles
• 25 degrees is the optimum temperature for yeast to respire
• Sugar is added to provide glucose for anaerobic respiration
• The ethanol produced as a product of anaerobic respiration by the yeast is evaporated
• The respiration of the yeast stops when the bread is baked because the hot temperature kills the yeast organisms
• Making yoghurt:

  • Pasteurise the milk by heating to 80-90 degrees
  • The milk is then cooled to 40-46 degrees
  • A starter culture containing live Lactobacillus is added
  • The culture is left to ferment for a few hours in a warm place (37-44 degrees)
  • Lactic acid is then produced, thickening the milk into yoghurt
  • Fruits and flavourings are added to the final product
  • Keep in the fridge at 5 degrees
• Milk contains a sugar called lactose, and Lactobacillus bacteria are able to break it down into lactic acid. The lactic acid lowers the pH which gives the yoghurt its sharp taste and causes the milk to clot and thicken. The acidity also prevents the growth of other microorganisms and acts as a preservative
• The milk is pasteurised to kill unwanted bacteria
• The pasteurised milk is cooled before the bacteria is added to reach the optimum temperature for the enzymes
• Lactic acid also denatures the protein enzymes causing the milk to clot and thicken
• To investigate the role of anaerobic respiration by yeast in different conditions:

  • Place 10ml of yeast and glucose solution in a boiling tube
  • Cover with a layer of oil to prevent oxygen diffusing into the mixture
  • Insert a rubber bung and delivery tube to form an airtight seal to the test tube containing 5ml of limewater
  • Time how long it takes for the limewater to turn cloudy
  • Repeat twice more, but placing the mixture in a water bath at 5 degrees and 40 degrees
• INDUSTRIAL FERMENTATION: Anaerobic process involving the use of microorganisms - Yeast, Bacteria etc, to commercially produce food products in a controlled environment
• ASEPTIC PRECAUTIONS

  Fermenter is steamed to kill Bacteria and prevent chemical contamination, only allowing desired microorganisms to thrive and carry out metabolic processes to produce desired product
• NUTRIENTS

  Nutrients are needed for organisms to release energy via respiration for growth, allowing metabolic reactions to occur to produce desired product
• OPTIMUM TEMPERATURE AND pH

  Temperature and pH probes are used to maintain an optimum environment for enzymes that carry out metabolic process in organisms, allowing organisms to thrive and produce desired product
• OXYGENATION

  Oxygen is needed organisms to release energy via aerobic respiration for growth, allowing metabolic reactions to occur to produce desired product
• AGITATION

  Agitation by stirring paddles ensure that microorganisms, Nutrients, Oxygen, temperature and pH is evenly distributed
• Motor and paddles agitate the mixture to mix the microorganisms with the nutrients and keep the temperature even
• Nutrient inlet allows nutrients such as glucose and amino acids to be added to the mixture, to allow the microorganisms to respire and grow
• Water cooled jacket absorbs excess heat to keep the temperature constant, because if the temperature is too high the enzymes denature and the microorganisms are killed
• Air inlet provides a source of oxygen for aerobic respirations
• Probes control internal conditions to keep them at the optimum temperature and pH for enzymes
• Air filter stops microorganisms getting in to keep the interior sterile and prevent contamination from unwanted microorganisms
• Steam inlet sterilises the inside of the fermenter when being cleaned to prevent contamination by unwanted microorganisms
• Industrial fermenters are used to make genetically modified bacteria for medicines such as insulin, and fungi for making the mycoprotein in Quorn