Food preservation

Question 1

What are the three main causes of food spoilage?

Answer 1

1. Biological (yeast, bacteria, molds)
2. Chemical (enzymes)
3. Physical (water loss/separation)

Question 2

Name 6 methods of food preservation

Answer 2

• High temperature
• Low temperature
• Dehydration
• Chemical preservatives
• Keeping out microorganisms
• Ionizing radiations

Question 3

What are the 4 ways of commercial drying?

Answer 3

1. Conventional (heat dry)
2. Vacuum (low pressure)
3. Freeze-drying (ice crystals vaporize)
4. Osmotic (strong syrup)

Question 4

What is curing?

Answer 4

Preservation with the use of salt and drying. It could also involve the addition of sugar, spices and nitrate, as well as smoking.

Question 5

Chemical changes occur during fermentation depends on:

name 3

Answer 5

• Raw material
• Selected microorganisms
• Processing steps

Question 6

What is pickling?

Answer 6

Preservation by acidification (addition of acid/vinegar OR fermentation)

Question 7

Why do we add edible coating to food? (4 reasons)

Answer 7

1. Increase shelf-life
2. Improves handling
3. Improves appearance
4. Vehicle for added ingredients

Question 8

What are the 2 methods of canning?

Which one is used for low pH items? Why?
Which one is used for high pH items? Why?

Answer 8

1. Boiling water process
   
   • for low pH items (pH 4.5 or below)
   • heat resistance of microbes is decreased by the acidic pH
2. Pressure canning
   
   • for high pH items (pH above 4.6)
   • The spores of Clostridium botulinum can survive in high pH and can only be killed with very high temperature

Question 9

What are the three methods in heat preservation?

How do they work?

Answer 9

1. Boiling
2. Pasteurization
   - 71 C (160 F) –> 15 sec
   - 138C (280F) –> 2 sec
3. Ohmic heating
   - electric current passing through food, generating heat

Question 10

What is sous-vibe?

Answer 10

Cooking food at a lower temperature for longer

Question 11

What are the temperatures for refrigeration and freezing respectively?

Answer 11

Refrigeration: above freezing to 4C

Freezing: -18C (0F) or lower

Question 12

What are the potential problems of freezing?

Answer 12

• Oxidation (Oxygen still present)
• freezer burn
• fluid loss
• cell rupturing (turgor loss)
• recrystallization

Question 13

Is rapid frozen or slow frozen more desirable? why?

Answer 13

Rapid frozen

Small and numerous ice crystals give better food quality

Question 14

What is freezer burn?

Answer 14

It is a dehydration on the surface of frozen food when water evaporates and recrystallizes on the surface.

Question 15

What kinds of oxidation might happen during freezing?

Answer 15

• Oxidation of polyphenolic substances in plant tissues by polyphenolases
• Oxidation of fat
• Oxidation of ascorbic acid by ascorbate oxidase

Question 16

What causes the development of off-odours in unbalanced/underblanched vegetables?

Answer 16

Accumulation of volatile carbonyl compounds

Question 17

Why do we blanch vegetables before freezing? (3 reasons)

Answer 17

1. Destroys enzymes that causes the development of off-odours
2. Controls undesirable changes in texture and colour
3. Inhibits conversion of bright green chlorophyll to olive green pheophytin

Question 18

What are the most common nutrient loss during freezing?

Answer 18

Vitamin C and B (especially folate)

Question 19

Describe 3 changes in colloidal substances during frozen storage.

Answer 19

1. retrogradation of starch and syneresis
2. toughening of cellulose
3. breaking of emulsion

Question 20

What are the foods that are approved by Health Canada for irradiation?

Answer 20

Spices, dehydrated seasoning preparations, wheat, flour, whole wheat flour, onions and potatoes

Question 21

What are the two ways of food packaging to increase shelf-life?

Answer 21

1. Aseptic packaging

2. MAP