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Option 9.6 - Preservatives
and Additives: 2. Food preservation techniques
Syllabus reference (October 2002 version) |
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| 2. Food preservation techniques began with simple procedures and commonplace substances and developed to include a wider range of chemical substances and principles | 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: 29 May 09]
Prior learning: Science Stages 4-5 syllabus: Outcomes 4.7.3, 4.7.6, Outcome 5.7.3f, Outcome 4.8 .3a, 4.8.5a.
Background: Some very early food preservation techniques were pickling in vinegar, drying and salting. These were probably first found accidentally. These practices occurred in Mesopotamia 5 000 years ago and in Africa at least 10 000 years ago.
distinguish between physical and chemical means of food preservation
- When a physical change occurs no new substance is produced and no chemical reaction occurs. There may be a change of colour when a substance is heated but the material goes back to its natural colour when it cools again. Examples of physical means of preservation would be pasteurisation by heating, freezing, drying and vacuum packing to exclude pathogens.
- Chemical means of preserving usually add a chemical. These chemicals either inhibit the activity of bacteria or kill the bacteria, therefore enabling the food to last a lot longer. Some chemicals that are commonly used to preserve food are benzoates (such as sodium benzoate), nitrites (such as sodium nitrite) and sulphites (such as sulphur dioxide).
- Another common preservative that you will see on food labels is sorbic acid. This or potassium sorbate (a salt of sorbic acid) prevents the growth of moulds, is safe and is used in many foods such as cakes, lollies, frozen pudding and icing.
plan, identify data sources, gather information and perform an investigation to compare the effectiveness of different physical means of preservation
- Decide which physical means of preservation you are going to do. You will need to consider which ones can be done with the equipment the school has.
- Consult your teacher and the laboratory assistant then plan your activity by writing a draft method. Consider safety issues in case you grow bacteria, and make sure you work under as sterile conditions as possible.
- Look in the school and local community libraries to identify information on methods of preservation. Use a search engine to find information from the Internet.
- Decide how long you are going to leave the food with the preservation techniques you are using and what criteria you will use as to the effectiveness of the preservation techniques.
relate
physical means of food preservation to killing or significantly limiting the
growth of micro-organisms through -canning
-freezing and refrigeration
-drying
-boiling (heating, including pasteursation)
-irradiation
-pickling
-salting
-vacuum packing
Canning
- This involves boiling the food in the container to kill all the bacteria and sealing the can (either before or while the food is boiling) to prevent any new bacteria from getting in. This sterilises the food so it will keep for a long period.
- Once you open the can, bacteria can enter and begin attacking the food, so you have to refrigerate the contents after opening and use within the recommended time.
- One problem with canning, and the reason why refrigeration or freezing is preferred to canning, is that the act of boiling food in the can generally changes its taste and texture (as well as its nutritional content).
Freezing and refrigeration
- Freezing does not destroy spoilage organisms but it stops their growth as long as the food is kept at -180C. Any bacteria present will become active as the food thaws so it is safest to thaw the food in the refrigerator.
- Any remaining food would then be kept in the refrigerator to slow the growth of organisms.
- Refrigeration will slow down the growth of bacteria and fungi but doesn't stop it completely as freezing does. Hence refrigeration only keeps food for days rather than the months that freezing does.
Drying
- Drying kills or completely inactivates most bacteria, especially if it is kept in air-tight containers.
- Normally drying completely alters the taste and texture of the food, but in many cases (such as raisins or sultanas) a completely new food is created that is flavoursome and popular in its own right.
- Freeze drying is a special form of drying that removes all moisture and tends to have less of an effect on a food's taste than normal dehydration does. In freeze drying food is frozen and placed in a strong vacuum. The water in the food then sublimates - that is, it turns straight from ice into vapour.
- Freeze drying is most commonly used to make instant coffee, but also works extremely well on fruits like apples.
Boiling (heating, including pasteurisation)
- Food can be made sterile by heating it to over 70°C (pasteurisation) with the bacteria being killed or by raising the temperature to over 120°C Ultra High Temperature (UHT). This higher temperature will kill all spores as well.
- Food is generally canned after heating so it will last for many months. One problem is that the act of boiling food generally changes its taste and texture (as well as its nutritional content). This is why many foods are pasteurised but not boiled.
Irradiation
- Irradiation is able to kill bacteria without significantly changing the food containing the bacteria. So if you seal food in plastic and then radiate it, the food will become sterile and can be stored on a shelf without refrigeration.
- Unlike canning only a few foods change the taste or texture of the food when you irradiate it. Some are: meat becomes darker and fish and seafood become mushy. Many vitamins, such as thiamine and niacin are not affected but other vitamins such as Vitamins A, E and K are destroyed.
Pickling
- Pickling was commonly used to preserve meats, fruits and vegetables in the past, but today is used to produce "pickles," or pickled cucumbers. Pickling uses the preservative qualities of salt (see below) combined with the preservative qualities of acid, such as vinegar (also known as acetic acid). An acidic environment inhibits bacteria.
- To make pickles, cucumbers are soaked in a 10-percent salt water solution for several days, then rinsed and stored in vinegar to preserve them for many years.
Salting
- Salting, especially of meat, is an ancient preservation technique. The salt draws out moisture and creates an environment inhospitable to bacteria. If salted in cold weather or under cold conditions, to prevent the meat spoiling before the salt has time to take effect, salted meat can last for years. The meat is cut into small salting blocks, and course salt is patted over the meat. It is then laid piece by piece into the container where it is going to be stored, careful that no two pieces touch each other. The slabs are laid like bricks, and salt is applied in the spaces.
- Today, salting is still used to create salt-cured "country ham" and corned beef and pastrami, which are made by soaking beef in a 10-percent salt water brine for several weeks.
Vacuum packing
- This preserves food as it removes the oxygen that would otherwise support organisms that attack the food such as fungi, bacteria and insects. As long as the package remains sealed the food will last for a much longer period of time than if it was just in the refrigerator.
plan, choose equipment or resources for, and perform a first-hand investigation to demonstrate the solubility of nitrates, nitrites and sulfites and relate this property to their role as food preservatives in cured meats
- Find out which nitrites, nitrates and sulfites are available and if any are dangerous to handle. The most common nitrate used for preserving is sodium nitrate, which slowly converts to sodium nitrite in the body. A chemistry teacher and/or the lab assistant will be able to check the records about safety.
- Research in books and on the Internet to see which of these specific chemicals is commonly used in preserving food, especially meats.
- Consider how much of the solute you will use and how much water (the solvent) to use.
- Decide what temperature you will have the water at and make sure it stays the same in all the tests (constant variable)
- You could put the solute and solvent in a large test tube and shake them. Make sure you do it for the same length of time for each of the solutes.
- Draw up a table to record the results. State if the salt was insoluble (didn't dissolve at all), partly soluble (dissolved at a high temperature but not at a lower temperature or partly dissolved), or fully soluble at a specific temperature.
relate
chemical food preservation to the use of chemicals to kill micro-organisms through
the use of
-nitrates
-nitrites
-sulfites
- Sodium nitrate is added to meats such as ham, bacon, hot dogs, luncheon meats and smoked fish. Nitrates break down in the body to nitrites and this stops the growth of bacteria, especially the bacteria that cause botulism poisoning. It also stabilises the red colour in cured meat and stops it turning grey.
- Sulfites include sulfur dioxide and sodium bisulfite. They prevent discolouration of foods such as dried fruit, dried, fried or frozen potatoes and "fresh" shrimp. They also prevent bacterial growth by interrupting the normal functioning of their cells, but they destroy vitamin B-1 and can cause severe allergic reactions, especially in asthmatics.
identify
preservatives and additives that are specifically designed to influence
-shelf life
-texture
-appearance
-flavour
and discuss some of the other effects of those additives
Shelf Life
- These chemicals make food last longer on the shelf or in your refrigerator by inhibiting the growth of organisms such as bacteria or fungi.
- Some are antioxidants
that retard the oxidation (reacting with oxygen) of fats and oils. Oxidation
leads to the food becoming rancid and losing colour. Some examples are:
Citric acid, EDTA (ethylenediamine tetraacetic acid), lactic acid, lecithin, mono and diglycerides, polysorbate 60, propyl gallate, sodium nitrate and nitrite, and sodium benzoate. - Most of these preservatives have no adverse side effects but there is some evidence that propyl gallate might cause cancer and sodium nitrite can lead to the formation of small amounts of cancer causing chemicals called nitrosamines. If ascorbic acid is added to bacon it will inhibit nitrosamine production.
Texture
- Most additives that improve
the texture of food are carbohydrates that thicken the food by absorbing some
of the naturally occurring water. They stabilise factory-made food by keeping
the products well mixed. Some example are:
alginate (a derivative of seaweed), starch and modified starch. - These additves don't have any adverse side effects but if a lot is added to food such as baby food they will replace other more nutritious ingredients. It is best to avoid too much added starch.
Appearance
- Many artificial colourings
have been added to food to make them look better. Many colourings cause hyperactivity
in some sensitive children. As well some studies indicate that many artificial
colourings may cause cancer. Some of them have been banned in the US and other
countries due to this risk. Some examples of additives that influence appearance
are:
- artificial colourings such as Red 40 (allura red AC-the most widely used food dye) used mostly in 'junk food', Yellow 5 (tartrazine-the second most widely used colouring) causes mild allergic reactions in some people, including asthma attacks and a rash in children. Also linked to thyroid tumours, chromosomal damage, hives and hyperactivity
- ascorbic acid (vitamin C) is a colour stabilizer as well as being a nutrient and preventing the formation of nitrosamines, which promote cancer
- beta-carotene is used as an artificial colouring and a nutrient supplement as it is converted to vitamin A in the body
- carmine (extracted from the eggs of the cochineal beetle). Red, pink and purple colours are produced. These colourings have caused allergic reactions from hives to anaphylactic shock
- sodium carboxymethylcellulose (CMC) is a thickening and stabilizing agent
- sodium nitrate and nitrite. Sodium nitrite is a colouring agent. See shelf life above for details.
Flavour
- Many of these additives
are artificial sweeteners and some enhance the natural flavours of the food.
It is not understood how flavour enhancers work. Some examples are:
- Acesulfame-K is an artificial sweetener that is used in chewing gum and soft drinks. Testing has been inadequate to definitely show it doesn't cause cancer.
- Aspartame (also known as Equal or NutraSweet) is used in lo-cal or diet food. Some people have experienced dizziness or headaches after drinking diet soft drinks but scientific tests haven't been done to gain further evidence. People with the rare disease PKU (phenylketonuria) should avoid aspartame.
- Dextrose is a source of natural sweetness in fruit and honey and is a common sweetener and colouring agent.
- Artificial and natural flavourings. Hundreds of chemicals have been used instead of natural flavours. Most are safe but they need to be used because there is little or no natural material in the food such as fruit. Companies keep the identity of their flavours a trade secret.
- Citric acid is naturally occurring in citrus fruits and is used to give food a tart flavour.
- Monosodium Glutamate (MSG) is a flavour enhancer but studies have shown that some people are sensitive to MSG with reactions such as headaches, nausea, difficulty in breathing and changes in heart rate.
gather and present information from secondary sources on preservation techniques used by different cultures
- Gather information by looking in encyclopedias and looking under the name of the culture such as Ancient Chinese culture or Egyptian culture. Also look on the Internet.
- For information on Aboriginal culture you should consult your local Aboriginal community. If you don't know how to contact them ask the teacher who is involved with Aboriginal Education and he/she will tell you if there is a local Aboriginal Education Consultative Group (AECG) and give you some details. Teachers should contact the Aboriginal education consultant in your district. Also look in The encyclopedia of Aboriginal culture, Australian Institute of Aboriginal and Torres Strait Islander Studies, 1994. It should be available in your school library.
- Present the information to the class in your chosen media, such as an oral presentation, accompanied by diagrams, photographs or slides. You could also submit a written report.
plan, choose equipment or resources for, and perform a first-hand investigation to determine the pH of a range of consumer products and relate this to the possible activity of micro-organisms in the manufacture of that product
- To plan your investigation you may decide to look in a book or on the Internet to find the pH of several different types of products so that you can choose a range of pHs in your investigation. Check which ones use micro-organisms in their manufacture.
- Research a range of indicators so you can choose appropriate ones to cover the approximate range of pHs you expect to get.
- Decide if you will need to treat the products before you add the indicator.
- Work out what type of table will be appropriate to record your results. The one below is an example.
| Consumer product | Indicator | Colour change | pH of the product |
- Choose the consumer products to use, including a variety of products and hopefully a range of pHs.
- Choose the equipment to use such as test tubes, test tube racks, mortar and pestle, etc.
- Perform the investigation, recording your results as each product is tested.
- If necessary redo any or use a different indicator if the results weren't clear with the indicator used.
- Record conclusions after assessing the results.
gather, process and present first-hand information to compare the ingredients and flow of table salt and cooking salt and relate this to the addition of free-flowing agents
- You could either do an investigation yourself in class to test the flowing ability of table salt and cooking salt and record the results or you could go to a salt processing factory and see if you can observe the flow of salts there. Write or phone the company first to ask if they will be able to show you.
- If you investigate the two yourself read the labels of the ingredients of both types of salt and record the similarities and differences in a table.
- Next work out a way you can compare the flow of the salts and then perform the investigation.
- Record the results and then repeat the investigation. If the results are very similar analyse the results and write conclusions about the flowing ability of the two types of salts. If the results don't clearly show a difference in the types of salts, repeat the investigation.
gather
information from the Australian Standards Food Code on the groups of additives
and preservatives such as
-anticaking agents
-antioxidants
-bleaches
-colouring agents
-emulsifiers
-flavouring agents
-humectants
-nutrients
-sweeteners
to identify the additives and preservatives in a range of consumer products
- The Australian Food Standards
Code is produced by Food Standards Australia New Zealand.
Some information about the functions of various additives can be found at the FSANZ
Website, Food Standards Australia New Zealand. - When you have found out what each of the additives and preservatives that you have chosen to investigate do, you could go to a supermarket or corner store and check the labels on a variety of foods in the store. Alternatively you could look at some cans and packets in the cupboards in the kitchen at home.
- Choose the form of food preservation you want to investigate.
- Go to a supermarket and start at one section such as condiments. Look at the back of the label on several of the products in this section. Each label should state what is in the product. Identify which of the ingredients are additives and/or preservatives.
- Record the additives in a table. The headings for the columns could be:
Food product Additive Impact on society
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