biology 1.7

• Food spoilage


  One of the main agents leading to the spoilage of food are microorganisms, in particular members of the bacteria, yeasts and moulds
• Pathogenic (or pathogens)


  Organisms that give rise to disease, either by the host ingesting live microorganisms (or microbes) which then grow in the host or by food-borne intoxication
• Food-borne intoxication


  Where the microbe releases toxic waste products as a result of their action in growing on or in the food. Poisoning occurs when the host ingests these toxins.
• Food stored or left at room temperature for any length of time provides an ideal set of conditions for pathogenic organisms to flourish
• Conditions for pathogenic organisms to flourish include temperature from 10°C-40°C, adequate moisture, optimum pH and a rich supply of nutrients
• A very common cause of food poisoning is caused by the toxin produced by Staphylococcus aureus
• Staphylococcus aureus


  • Quite resistant to a range of harsh conditions, able to survive temperatures of 60°C for 30 minutes, resistant to some radiation and high solute concentrations
• In Australia, many steps have been put in place to ensure that human health is not adversely affected by food spoilage or contaminated food
• Hygienic practices in the food industry

  • Sanitisation
  • Personal hygiene
  • Cleaning equipment
  • Storing food
• Sanitisation


  Keeping workbenches clean and sanitised by using disinfectants, ensuring all areas where food is prepared is free from vermin, insects, dirt etc. which may harbour or transmit microbes
• Personal hygiene


  Washing hands frequently, avoiding coughing and sneezing near food, wearing proper clothing and paying attention to good personal hygiene with hair tied back or the use of a hair net
• Cleaning equipment


  Ensuring all cooking utensils are cleaned thoroughly and regularly, cleaning all knives, plates and surfaces regularly, using high temperature and pressure apparatus to clean surfaces and utensils
• Storing food


  Correctly using refrigeration, adhering to use-by dates, ensuring adequate cooking
• The four core practices for hygienic food management are: CLEAN, SEPARATE, COOK, CHILL
• Canning temperature for some vegetables and meats is 120°C, for fruits and tomatoes is 100°C
• Warming ovens have little bacterial growth, some bacteria survive
• Rapid growth of bacteria occurs in the danger zone, with toxins released
• Some bacterial growth occurs at temperatures below the danger zone, causing food spoilage, but limited growth of pathogens
• Foods frozen, bacteria do not grow but many survive
• Some preservation methods date back thousands of years, and the discovery of better methods of preserving food has been an important aspect of modern civilisation
• Food spoilage is caused primarily by the action of bacteria, yeasts and moulds, so any processes or techniques that inhibit microbial growth in food, whilst still maintaining the taste and texture, quality and appeal, will help to prolong food life
• Traditional methods of food preservation


  • Figure 176(a), Figure 176(b)
• Modern methods of food preservation

  • Figure 177
• Range of preservation methods

  • Heat sterilisation/boiling/steam
  • Pasteurisation
  • Refrigeration
  • Deep freezing
  • Drying
  • Radiation
  • Chemical preservatives
  • Commercial sterilisation
• Heat sterilisation/boiling/steam


  Kills bacteria and fungi in 10 minutes
• Pasteurisation


  Heat treatment for milk at 72°C for 15 seconds kills most bacteria
• Refrigeration


  Slows cell metabolism and bacterial growth at approximately 5°C
• Deep freezing


  Freezing makes liquid water unavailable to microbes which greatly slows their growth and reproduction
• Drying


  Removes moisture from microbes and the food itself and kills most pathogens since they lose water
• Radiation


  Destroys DNA and kills pathogens
• Chemical preservatives


  e.g. acids, sugars, sodium nitrite, salt and smoke destroy pathogens
• Commercial sterilisation


  This process kills pathogens and the food is then stored in a sealed container until use