Past Exam Questions

Question 1

Discuss the main causes of food spoilage
(Enzyme action)
(3 headings)
(4, 3, 3)

Answer 1

Enzyme action:

1. Ripening
   - Sweetness improves as the high starch content converts into sugars such as fructose
   - A colour change takes place such as tomatoes changing from green to red
   - A texture change takes place such as bananas changing from hard to soft and easily digestible
   - The enzymes will bring about the overripening of the food and will bring about the decay and decomposition of food
2. Enzymic Browning
   - When some fruit or veg is cut an enzyme called oxidase is released with their cell walls
   - Oxidase reacts with oxygen in the air and turns the food brown and eventually causes food spoilage
   - Oxidation of oxidase reduces vitamin C
3. Enzymic deterioration
   - fish naturally contain enzymes which speeds up the spoilage and deterioration of their flesh even at low temperatures
   - these enzymes bring about the spoilage and deterioration of the fish’s flesh
   - the deterioration of the flesh produces a putrid smell

Question 2

Discuss the main causes of food spoilage
(Moisture loss)
(6 main points)

Answer 2

Moisture loss begins once the fruit or veg is harvested as they lose their ability to absorb water from the soil through their roots
Moisture loss causes fruit or veg to become dehydrated
Shrinkage can occur e.g. mushrooms shrivel
Wrinkling can occur e.g. apple or pepper skins wrinkle
Limp appearance in asparagus and celery
The surfaces of high protein foods such as cheese become hard

Question 3

Discuss the main causes of food spoilage
(bacteria)
(2 main points)

Answer 3

Cause both internal and external food poisoning

They produce endotoxins and exotoxins which are not visible

Question 4

Discuss the main causes of food spoilage
(moulds)
(3 main points)

Answer 4

Moulds produce visible food spoilage but rarely cause food poisoning as people tend to avoid visibly spoiled food
Moulds produce mycotoxins which are carcinogenic
The toxin aflatoxin is produced by the mould Aspergillus flavus

Question 5

Name two food poisoning bacteria

Answer 5

Salmonella

Clostridium Botulinum

Question 6

Describe salmonella

Answer 6

Rod-shaped
Reproduces asexually by binary fission
Contagious
Facultative
Mesophilic
Causes infectious food poisoning
Gram negative
- cell wall with 2 thin layers
- has flagella
- no spore production
- high resistance to antibiotics

Question 7

Describe clostridium botulinum

Answer 7

Rod-shaped 
Reproduces asexually by binary fission 
Not contagious 
Anaerobic 
Mesophilic 
Causes toxic food poisoning 
Gram positive
- cell wall is 1 thick layer 
- does not have flagella 
- produces endospores 
- low resistance to antibiotics

Question 8

Describe the habitat for salmonella

Answer 8

Intestines of animals and humans
Human and animal waste
Unwashed hands

Question 9

Describe the habitat for clostridium botulinum

Answer 9

Soil
Decaying matter
Vegetables
Pig intestines

Question 10

What conditions are necessary for the growth of clostridium botulinum

Answer 10

Anaerobic
- does not require oxygen for growth 
Mesophilic 
- Optimum pH between 30 and 37 degrees Celsius
pH
- slightly acidic environment (4.6)

Question 11

How does clostridium botulinum reproduce?

Answer 11

Reproduces asexually by binary fission

• bacterial cell elongates
• its nuclear material (DNA) duplicates
• a cell wall and membrane forms between the duplicated DNA and the original to create two separate identical bacteria

Question 12

What are high risk foods associated with clostridium botulinum?

Answer 12

Unpasteurised cheese
Canned food
Vacuum-packed food

Question 13

Explain how blanching assists in controlling enzymic food spoilage

Answer 13

Blanching involves immersing vegetables in boiling water for five minutes and to destroy enzymes and then plunging them in ice cold water before freezing to prevent cooking

Question 14

How do cold temperatures control enzymic spoilage?

Answer 14

Low temperatures slow down enzyme activity in food, reducing the rate of spoilage and lengthening shelf life

Question 15

How do acids control enzymic spoilage?

Answer 15

Acids lower pH levels which inactivates enzymes which work best at neutral pHs

Question 16

Differentiate between toxic and infectious food poisoning

Answer 16

Infectious food poisoning;

• An illness caused by eating food containing pathogenic bacteria that produce endotoxins
• endotoxins are released when the bacterial cell dies
• endotoxins are destroyed easily by normal cooking temperatures
• It has a long incubation period of over 12 hours
• Salmonella or E.coli

Toxic food poisoning:

• An illness caused by eating food containing pathogenic bacteria that produces exotoxins
• exotoxins are released before or after the food is eaten
• exotoxins are difficult to destroy and can be destroyed by 30 minutes of boiling
• It has a short incubation period of around 2 hours
• Staphylococcus aureus or Clostridium botulinum

Question 17

Name three common food poisoning bacteria

Answer 17

Salmonella 
E.coli 
Listeria 
Staphylococcus aureus 
Clostridium botulinum

Question 18

How do additives/preservatives control enzymic spoilage?

Answer 18

Sulfur dioxide is a preservative which inactivates enzymes and is used commercially to prevent enzymic spoilage

Question 19

How does heat control enzymic spoilage?

Answer 19

Enzymes are sensitive to high temperatures and are inactivated by cooking

Question 20

What are the symptoms of botulism (clostridium botulinum food poisoning)?

Answer 20

Diarrhoea
Slurred Speech
Double Vision
Paralysis of the throat
Dizziness
Death