Food Spoilage & Contamination (AQA GCSE Food Preparation & Nutrition): Flashcards
Exam code: 8585
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Define food spoilage.
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Define food spoilage.
The loss of food quality that causes food to become inedible.
Which three microorganisms can cause food spoilage?
bacteria
yeast
mould
State the four conditions microorganisms need to grow.
the correct temperature
water (moisture)
food, to provide nutrients
the correct pH
To reach harmful levels, microorganisms also need a sufficient length of ＿＿＿＿＿＿＿＿ under suitable conditions.
To reach harmful levels, microorganisms also need a sufficient length of time under suitable conditions.
How can temperature be used to control microorganism growth?
Reduce the temperature, e.g. by refrigerating or freezing.
Increase the temperature by cooking the food.
Reduce the time food is left at room temperature.
How can pH be used to control microorganism growth?
Provide an acidic environment, e.g. by pickling in vinegar, as most microorganisms cannot survive at a very low pH.
How can water availability be used to control microorganism growth?
Remove the water, e.g. by drying, salting or adding lots of sugar.
Define high risk food.
A ready-to-eat, moist food, usually high in protein, that easily supports the growth of pathogenic bacteria and needs no further cooking.
Name four high risk foods.
Any four of:
cooked meat and fish
dairy products, e.g. cheese and milk
egg and foods containing egg, e.g. mayonnaise
precooked shellfish, e.g. mussels and prawns
gravy, stock and sauces
cooked rice
Why are high risk foods particularly dangerous?
They will not undergo further heating before being eaten, so any microorganisms present are not destroyed.
What are enzymes, and what are they made of?
Biological catalysts made of protein, which speed up chemical reactions.
State two ways of controlling enzymic action in food.
heating, e.g. blanching vegetables before freezing
adding an acid, e.g. lemon juice on sliced apple
True or False?
All microorganisms found in food are harmful.
False.
Not all microorganisms are harmful, but some cause food spoilage and may result in food poisoning if eaten.
What are the two main causes of the signs of food spoilage?
Enzymic action, and the growth of microorganisms — mould, yeast and bacteria.
Give two signs of food spoilage caused by enzymic action.
Enzymic browning of sliced fruit such as apples and pears.
Fruit becoming overripe, e.g. bananas and avocado.
What are moulds, and how do they spread?
Fungi that spread by the growth of thread-like filaments.
State four conditions in which moulds can grow.
Any four of:
acid or alkaline
high sugar
high salt
moist or quite dry, e.g. on hard cheeses
warm temperatures
How can you recognise mould growth on food?
Visible growth that is green, black or white in colour, often with a furry appearance.
True or False?
Cutting the mould off a food makes the rest of it safe to eat.
False.
Mould visible on the surface shows that microscopic moulds are already present within the food.
Name three foods on which moulds commonly grow.
Any three of:
bread
cheese
jam
fruit
What are yeasts, and what conditions do they need to grow?
Single-celled fungi.
They grow with or without oxygen, and need enough moisture and warm temperatures.
On which types of food do yeasts commonly grow?
Acidic, sweet foods, e.g. fruit such as grapes, strawberries and tomatoes, fruit juice, honey, jam and sweetened yoghurt.
Yeasts growing in the absence of oxygen ＿＿＿＿＿＿＿＿ the sugars in food.
Yeasts growing in the absence of oxygen ferment the sugars in food.
State three signs that yeast has spoiled a food.
gas bubbles of carbon dioxide on the surface of liquids
an alcoholic taste
a slightly fizzy mouthfeel
Why do sliced apples turn brown when left out?
Oxidation on exposure to air, sped up by enzymes — a process called enzymic browning.
State the three uses of microorganisms in food production.
moulds in the production of blue cheese
yeasts to raise bread
bacteria in yoghurt and cheese production
What does mould do to blue cheese?
It gives a creamy texture, a sharp, tangy flavour, and visible blue and green veining.
Name three blue cheeses made using mould.
Stilton
Gorgonzola
Roquefort
True or False?
Any mould could be used to make blue cheese.
False.
The moulds used are chosen specifically and do not cause harm. Other moulds would not work the same way and may be harmful to eat.
Describe how yeast is used to make bread.
Yeast is mixed with flour and water and kneaded, to form gluten and distribute the yeast.
The yeast respires using sugars, releasing carbon dioxide.
The gas forms bubbles that make the dough rise during proving.
Baking expands the gas further.
Why is bread dough kneaded before proving?
To form gluten and to distribute the yeast evenly through the dough.
Define starter culture.
The useful bacteria added to milk at the start of yoghurt production.
Why is milk boiled before yoghurt is made?
To kill any non-useful or harmful bacteria already present.
Describe how bacteria turn milk into yoghurt.
The milk is gently heated so the bacteria can respire using its sugars — this is fermentation.
They produce lactic acid, which denatures the milk proteins and makes them coagulate.
The milk thickens and turns sour.
The bacteria used in yoghurt production produce ＿＿＿＿＿＿＿＿, which denatures the proteins in milk.
The bacteria used in yoghurt production produce lactic acid, which denatures the proteins in milk.
Which enzyme is added during cheese making, and what does it do?
Rennet, which makes the milk separate into liquid whey and solid curds.
What happens to the curds after the whey is removed?
They are heated, pressed and salted to produce a solid block of cheese, which may then be left to mature.
Why is salt added during cheese making?
It adds flavour and acts as a preservative to prevent spoilage.
Name the five types of food poisoning bacteria in the specification.
campylobacter
e-coli
salmonella
listeria
staphylococcus aureus
What are the main sources of campylobacter?
Raw poultry and other meat, and untreated water and milk.
What are the main sources of e-coli?
Raw beef, untreated water and milk, and unwashed salad.
What are the main sources of salmonella?
Raw poultry, and untreated milk and eggs.
What are the main sources of listeria?
Soft cheese, pâté and shellfish.
The main source of staphylococcus aureus is human and animal ＿＿＿＿＿＿＿＿.
The main source of staphylococcus aureus is human and animal hair and skin.
State the five sources of bacterial contamination.
other contaminated foods
work surfaces and equipment
the people cooking
pests
waste food and rubbish
How can contamination from other foods be prevented?
separate raw and cooked food during storage
store defrosting raw food at the bottom of the fridge so it cannot drip onto other food
wash raw vegetables thoroughly to remove soil bacteria
How can contamination from surfaces and equipment be prevented?
wipe surfaces with antibacterial spray before preparing food
clean equipment with hot water and soap after use
use separate chopping boards for raw and cooked food
use clean cloths every day
How can the person cooking avoid contaminating food?
Any of:
wash hands before cooking, between different foods, and after touching the mouth or nose
use a clean spoon every time food is tasted
hold utensils by the handles
wear a hair net and clean gloves, and cover cuts
How do pests contaminate food, and how can this be prevented?
Rodents and insects transfer bacteria from their bodies, urine or faeces.
Prevent it by keeping doors and windows closed, covering and emptying bins, not leaving food out overnight, and covering food as it cools.
Why should bins have foot-operated lids?
So that hands do not touch the bin and then the food, which would transfer bacteria.
State the general symptoms of food poisoning.
vomiting
nausea
diarrhoea
stomach pain
fever
True or False?
Food poisoning is never life threatening.
False.
Serious cases can result in death, especially in vulnerable individuals.
Which groups should avoid high risk foods?
At-risk groups — the very young, the elderly and pregnant women.
Define pasteurisation.
Heating milk to a high temperature to kill bacteria before it is sold in shops.
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