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Option 9.6 - Preservatives
and Additives: 3 Spoilage of food
Syllabus reference (October 2002 version) |
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| 3. Microbial activity is responsible for spoilage and the loss of appeal | Students learn to:
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Students:
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Extract from Senior Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.
[Edit: 12 May 11]
Prior learning: Science Stages 4-5 syllabus: Outcome 4.8.3a and b.
gather, process, analyse and present information from secondary sources to identify the causes, symptoms and treatments for food poisoning
- Gather information on food poisoning by looking in health and medical books and the Internet. Use a search engine and type in words such as 'food poisoning', 'causes', 'symptoms', 'treatment'.
- When you have enough information, arrange it so you can process it by comparing the different sources to evaluate which information is the most suitable for your purposes. If there is conflicting information check another source. You may use your teacher as a source of information. If he/she doesn't know he/she will help you to verify if what you have decided is valid information.
- When you have compiled the information in the best way to use it, you can analyse it to make generalizations about causes, symptoms and treatment of food poisoning.
- Present your information in a clear and concise form to the teacher and/or to the other students. You might choose to use headings and tables to assist you in your presentation.
Some good web sites for
information on
food poisoning 
Health Encyclopedia- Diseases and Conditions, Food Poisoning, USA Today,
Worldwide increases in
foodborne illness, Food Poisoning in Australia, Romsey Australia, April 2011
gather, process, analyse and present information from first-hand and secondary sources to identify contamination risks in the preparation of food and discuss ways that these risks may be minimised
- To gather first hand information your teacher may arrange for you to go to a food factory that is in the local area. Decide on some questions to ask your guide to be sure she/he includes the information you need. Take notes as the person speaks then organise your notes when you are back at school. Gather secondary information by looking in encyclopedias, home economics books, health books and on the Internet.
- Process the information by comparing material from different sources. Did you find that what you read in the literature is similar to what you found when you visited the factory?
- Analyse the information to see that you have adequately covered the issue of contamination risks in the preparation of food. Do you have information on the way these risks can be minimized? If not you will have to go back to your sources and find more information.
- Present information in visual and written form. You might decide to make a video of your excursion and incorporate that into your presentation. Alternately you may decide to do a powerpoint presentation.
identify
common microbes that cause spoilage including
-Campylobacter
-Clostridium
-Escherichia coli
-Salmonella
-moulds and fungi
- Campylobacter jejuni enteritis is primarily transferred from animal origin foods (such as chicken, beef, pork and lamb) and unpasteurised milk to humans.
The bacteria grow poorly in food, therefore hygienic slaughter and processing procedures, with thorough cooking of meat and poultry products followed by proper storage should result in less contamination.
- Clostridium perfringens is found in soil, dust and the gastrointestinal tracts of animals, including people. When food containing a large number of C. perfringens is consumed, the bacteria produce a toxin in the intestinal tract that causes illness.
C. perfringens can exist as a heat-resistant spore, so it may survive cooking and grow to large numbers if the cooked food is held between 5 degrees C and 60 degrees C for an extensive time period.
- Clostridium botulinum Botulism is not a common source of food poisoning but it has caused death in approximately 30 percent of the cases reported and it occurs mostly in home-canned foods.
Cl. botulinum can exist as a heat-resistant spore, and can grow and produce a neurotoxin in under processed, home-canned foods.
- Enteropathogenic Escherichia coli is a significant cause of diarrhoea in developing countries and localities of poor sanitation. It has been associated with "travellers' diarrhoea."
The major source of the bacteria in the environment is probably the faeces of infected humans, but there may also be animal reservoirs. Faeces and untreated water are the most likely sources for contamination of food.
- Salmonella The gastrointestinal tracts of animals, including people are common sources of Salmonella. High protein foods such as meat, poultry, fish and eggs are most commonly associated with Salmonella. However, any food that becomes contaminated and is then held at improper temperatures can cause salmonellosis. Salmonella are destroyed at cooking temperatures above 65 degrees C.
Control of enteropathogenic E. coli and other food-borne pathogens such as Salmonella and Staphylococcus aureus can be achieved. Precautions should include adequate cooking and avoidance of recontamination of cooked meat by contaminated equipment, water or infected food handlers. Food service establishments should monitor adequacy of cooking, holding times and temperatures as well as the personal hygiene of food handlers.
gather and process information from secondary sources to discuss the use of ultra high temperatures (UHT) as a preservative technique
Background information
"UHT is a commercial sterilisation process that has been in use since its introduction in 1948. UHT processing heats
milk products within a range of 138 C to 150 C (nearly twice the temperature of pasteurisation) for 4 to 15 seconds. Coupled with aseptic packaging, UHT processing can help extend shelf life for up to six months or more without refrigeration. This resulting product fits into the shelf-stable dairy beverage category. The total procedure involves sterilising the milk through UHT processing and filling and sealing it in an aseptically sterilised package (packaging free of bacteria). To prevent the recontamination by microbes, gases or airborne bacteria, the final container will be hermetically sealed. Despite the advantage of UHT processing, extended thermal treatment and subsequent ambient storage can result in the development of off-flavours, sometimes described as "cooked" flavour, as well as the loss of vitamins and amino acids. To combat these defects and attain extended shelf life, some processors have employed UHT processing temperatures at the minimal safe times, in conjunction with aseptic packaging."
Innovations in Dairy, Dairy Industry Technology Review, October, 2001.
- Find information about UHT treatment such as what is done, how it is done and the effectiveness of the treatment. Use text books, CD-ROMS and the Internet to gather the information.
- Find out any advantages of UHT over heating to lesser temperatures, such as temperatures used for pasteurisation. Are there any disadvantages to this method?
- Discuss your findings with your fellow students. Some information
can be gathered at
Pasteurization Wikipedia, the free encyclopedia, 2011
describe
the conditions under which many micro-organisms grow and reproduce in terms
of
-temperature
-pH
-water availability
Temperature
- Most micro-organisms grow and reproduce well in warm conditions. There are some though, that like very high temperatures and these live in places such as hot springs. There is an upper limit and if this is exceeded the micro-organisms will die. There is also a lower limit where they will not grow and reproduce under the limit, but they don't usually die, just remain inactive until temperatures warm again.
pH
- Most food spoilage organisms prefer a pH in the slightly acidic to neutral pH range. By adjusting the pH of the food it will be less likely to spoil due to bacteria.
Water availability
- Bacteria, and moulds must have water to reproduce and thrive. The easiest way to remove water is to boil or bake the food. Another way that causes less change to the food is to heat gently, thereby removing the water slowly. The sun is sometimes used to dry food.
perform a first-hand investigation to model osmosis
Background information
Osmosis is the movement of water from an area of high concentration of the
water (ie low concentration of the solute) to an area of lower concentration
of the water (higher solute concentration), across a semi-permeable membrane.
- As bacteria are so small and therefore difficult to see, you could perform the investigation to model osmosis using an artificial cell. Take some dialysis tubing and tie a knot in one end. Place a salt solution, such as a 5% sodium chloride solution, in the tube. Lower the tube into a beaker of a much stronger solution such as 15% sodium chloride. Mark the level of the solution in the tubing and leave it for about 24 hours.
- Observe the level of the solution and use your own words to explain what has caused the change. If there is no change check the tubing for a leak.
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