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FN 132 > Low Temperature Preservation > Flashcards

Low Temperature Preservation Flashcards

1
Q

Where was food stored before any kind of low temperature preservation technologies?

A

Cold cellars
Holes in the ground
Natural caves

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2
Q

When did ice became a widespread means of cold preservation?

A

Middle 1800s

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3
Q

What was the first refrigerator called? Also, describe.

A

Ice box. A close wooden box with two compartments. Top compartment has the ice. Lower compartment has the food.

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4
Q

When was mechanical refrigeration introduced?

A

late 1800s

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5
Q

Chilling/refrigerated storage

A

Storage of foods above freezing and below 15 C (59 F)

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6
Q

Chilling is only a short-term preservation because of

A

Growth of microorganisms
Moisture loss
Post Harvest/-slaughter metabolic activities of intact plant and animal tissues
Deteriorative chemical reactions - autolysis of fish, nutritional loss, color degradation

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7
Q

What causes loss of moisture in chilling?

A

Low humidity inside the refrigerator

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8
Q

Does psychrophilic bacteria cause spoilage?

A

Yes.

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9
Q

Chilling injury

A

When fruits and vegetables develop physiological disorder because they are exposed to temperatures below optimum storage but above their freezing points.

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10
Q

Types of cooling methods

A

Blast chillers
Hydro coolers
Vacuum coolers

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11
Q

Blast chillers

A

Operate by passing cold air over food at high speed

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12
Q

Blast chillers
Air speed:
Air temperature:

A

Blast chillers
Air speed: 4 m/s
Air temperature: 4 C

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13
Q

Hydro coolers

A

Use of chill water, by spraying or immersion

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14
Q

In hydro coolers, there is no risk of ?

A

Freezing

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15
Q

Hydro coolers sometimes use

A

Fungicides

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16
Q

Hydro coolers are suitable for products…

A

Not affected by water

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17
Q

Vacuum coolers are mainly applied for

A

Pre-packed leafy vegetables with large surface area

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18
Q

Vacuum coolers

A

Food is placed in a vacuum chamber and the pressure is reduced to ~0.5 kPa.

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19
Q

Sous vide meaning

A

French - under vacuum

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20
Q

How does sous vide work?

A

Raw food is vacuum sealed in heat-stable, food-grade plastic pouches. These are cooked using precisely controlled heat (temperature and time).

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21
Q

Benefits of vacuum sealing in sous vide

A

Inhibits off-flavors due to oxidation

Prevents the loss of flavor volatiles and moisture during cooking
Reduces aerobic bacterial growth

22
Q

Process of sous vide

A

Raw or par-cooked food

Vacuum sealing in plastic pouches

Heat treatment (controlled cooking)

Rapid chilling

Reheated for service

23
Q

Dangers of sous vide

A

Pasteurization does not reduce pathogenic spores to a safe level. If not chilled rapidly enough or refrigerated for too long —> grow in dangerous levels

24
Q

Chilled storage period of sous vide

A

21 days at 0-3 C

25
Q

Minimum recommended thermal process for sous vide is

A

90 C for 10 mins or its t-T equivalent

26
Q

Freezing

A

Unit operation in which the temperature of food is reduced below the freezing point and a proportion of water undergoes phase change to firm ice

27
Q

Principle of freezing

A

1) Lowering of temperature by the removal of heat
2) Change from liquid to solid

28
Q

For a product to freeze, it must be cooled…

A

Below its freezing point

29
Q

Explain the process of freezing.

A

Water component freezes —> dissolved solids are left in a more concentrated solution —> this solution requires a lower temperature to freeze

30
Q

True or false. In freezing, all water content is frozen.

A

False.

31
Q

Fast freezing

A

Produces small crystals

For ice cream, fruits, and carrots, peas, and corn.

32
Q

Main difference between slow and fast freezing.

A

Slow freezing result in shrunk cells and destructed tissue. Meanwhile, fast freezing maintains integrity of the cell and there are less damages to the tissue.

33
Q

Quality changes due to freezing are encompassed by two phenomena

A

Freezing concentration effect
- loss of consistency
- syneresis
- chemical rxns

Large ice crystal damage and recrystallization
- physical rupture of cell walls and membranes and separation of plant and animal cells
- disruption of emulsion, foams, and gels

34
Q

When does freezer burn occur?

A

There is headspace in the packaged food

Subjected to fluctuating temperatures

35
Q

In freezer burns, there is _____ ______ because of fluctuating temperatures.

A

Moisture loss

36
Q

Types of freezing equipment | cooled air freezer

A

Chest/still air cabinet freezer
Blast freezer
Belt freezer
Fluidized bed freezer

37
Q

Still Air Cabinet freezer

A

Chest or cabinet systems

38
Q

Chest vs cabinet freezer

A

Chest
- retain cold air

Cabinet
- lose cold air when door is opened

39
Q

Advantage of still air cabinet freezer

A

Relatively simple, versatile, cheap

Used as storage after freezing

40
Q

Disadvantage of still air cabinet freezer

A

Slow freezing

41
Q

Blast freezer
Air speed:
Air temperature:

A

Blast freezer
Air speed: 400 m/min —> rapid heat transfer
Air temperature: -25 to -36 C

42
Q

Advantage of blast freezing

A

Many types (spiral, cabinet, belt)
Fast freezing but slower than plate freezing

43
Q

Disadvantages of blast freezing

A

High capital cost
Moisture loss can be a problem

44
Q

Thawing

A

Application of heat until the ice present has reverted to water

45
Q

True or false. Thawing can be more damaging than freezing.

A

True

46
Q

Main considerations in thawing

A

Avoid overheating
Minimize thawing times
Avoid excessive dehydration

47
Q

Thawing vs freezing

A

1) Thawing is slower
2) Thawing has less temperature differential
3) Thawing is usually less controlles
4) Thawing’s time temperature pattern may be more detrimental
5) Refreezing may be done in thawing

48
Q

Thawing is microbiologically okay if

A

Temperature is low

49
Q

How is thawing product dependent?

A

Quality must not suffer when planning to refreeze

50
Q

How to ensure that refreezing after thawing is still microbiologically okay?

A

Remanufacture
Cook and refreeze
Test for microorganisms if not sure

51
Q

Thawing time of frozen egg pulp using a microwave

A

15 mins

FN 132 (4 decks)

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