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Do you remember what ways can prevent food from spoiling in AS/A-level Biology?
Processes that Affect Microorganisms
- When food is created using microorganisms, there needs to be controlled conditions otherwise food will be spoiled as microorganisms will grow etc.
- There are six types of treatment that you need to know about that affect microorganisms:
- Freezing
- Adding sugar
- Adding salt
- Pickling
- Heat treatment
- Irradiation
- Methods to prevent further contamination include:
(i) Canning - the food is heated and sealed in airtight cans
(ii) Vacuum wrapping - air is excluded so microbes cannot respire aerobically
(iii) Any plastic or paper packaging
Freezing
- Some foods can be freeze dried, e.g. fruits, and this is done via putting the food into a vacuum, and this keeps food below minus eighteen degrees Celsius.
- The food does not freeze, the low pressure surrounding the food items turn into water vapour.
- This does less damage as ice could pierce and break cell membranes.
- Food keeps its texture better than conventional freezing.
Salting and Adding Sugar
- Salting is traditionally used for meat, fish and some kinds of vegetables.
- Salt may be rubbed into the food or the food is submerged into a low potential solution.
- This interferes with the microorganism’s ability to absorb water (which they need to survive).
- This largely changes the flavour but many people like salted meats such as ham.
- It is also used with sugar to prevent micro-organism s growing in jams or marmalades.
Pickling
- Enzymes and other proteins may denature if placed in an acidic solution.
- Vinegar (an alkali) is often used for products such as pickles and they keep the food at its original condition.
Heat Treatment
- Microorganisms are killed by extreme heats; some heat-resistant pores can survive above 100 degrees.
- The temperature in kitchen ovens can cause the microorganisms to die, this is due to the intense heat and this has been adapted for the use in the food production industry.
- Pasteurised milk is an example, it does not kill all of the bacteria (heats up to 65 degrees and then cools down to 20 degrees), and this is why milk can be stored for five days.
- UHT (Ultra High Temperature) milk kills all bacteria as the milk is boiled and stored in a container.
Irradiation
- Gamma radiation is often used.
- Radiation can cause a change in chemicals in some food but there is no proof that it affects health.
Production of Food
Bread
- It is made by mixing yeast, sugar, flour and water into a dough.
- The yeast turns the sugar into ethanol and carbon dioxide.
Wine
- This is made by adding yeast to grape juice.
- The yeast turns the sugar in the grape juice into ethanol and carbon dioxide.
Yoghurt
- This is made by adding bacteria to milk.
- The bacterium turns the sugar in the milk to lactic acid causing the milk to clot and thicken into yoghurt.
Cheese
- This is also made by adding bacteria to milk.
- The bacterium turns the sugar in the milk into lactic acid, which causes the milk to curdle.
- An enzyme is then used turn the curdled milk into curds and whey.
- The curds are separated off and left to ripen into cheese.
Advantages of Microorganisms
- Cheaper to work with than field crops or animals.
- They can be cultured anywhere as long as they are not reliant on certain conditions.
- Grown all year round.
- Unaffected by weather which affects crops.
- This can be grown from waste products.
- They grow quickly giving high yields and fast production.
- No ethical issues
- Low fat or no fat foods.
Disadvantages of Microorganisms
- Foods such as mycoprotein aren’t as interesting as conventional food.
- Specialist labs are usually needed to control microorganism production. This many not be possible in countries that focus on agriculture.
- They are subject to infections.
- Production vessels can be contaminated.
That's the end of the topic!
Drafted by Bonnie (Biology)