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FN3342 - Advanced Food Science > Freezing and Concentrations > Flashcards

Freezing and Concentrations Flashcards

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1
Q

What happens to leftovers in the refrigerator?

A

1) Slow microbial growth

2) Enzymatic changes that may cause off flavour

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2
Q

What do think are the most important factors for older adults to know about refrigeration?

A

1) Refrigerate foods ASAP
2) Pack foods in small portions
3) Avoid cross contamination

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3
Q

TRUE or FALSE?

Fruits and vegetables coming into storage are usually contaminated, especially with mold spores

A

TRUE

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4
Q

If freezing stops growth of bacteria, why does frozen foods have a best before date?

A

1) Quality

2) Sensory properties

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5
Q

TRUE or FALSE?

Freeze concentration can increase the concentration of enzymes and their substrates and result in faster reaction rates

A

TRUE

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6
Q

TRUE or FALSE?
The speed of liquid nitrogen freezing produces frozen foods with a quality unattainable by non-cryogenic freezing methods

A

TRUE

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7
Q

In cryogenic liquids, cold temperature result from __________ of liquid nitrogen and CO2

A

Evaporation

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8
Q

TRUE or FALSE?

Some products such as mushrooms cannot be frozen by other methods without excessive tissue damage

A

TRUE

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9
Q

What is the reason for choosing -18 degrees C for freezing?

A

Enzymes are very resistant to cold temperature and may stay active at even -18 degree C

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10
Q

What are other methods of processing that may yield products equal or nearly equal in quality to those obtained by freezing?

A

1) Concentration followed by freezing (orange juice)
2) High temperature short time (HTST) followed by ascetic packaging
3) Irradiation

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11
Q

Refrigerated or chilled foods are foods that are stored at temperatures below __________ and above __________

A

15 degrees C; 0 degrees C

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12
Q

Apple may become __________ if stored at too __________ a temperature, and bananas turn dark in the __________

A

Soft; cold; refrigerator

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13
Q

____________________ in potatoes is a phenomenon that causes potatoes to accumulate sugar (from the conversion of starch) during cold storage

A

Chill sweetening

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14
Q

Cold shortening in meats results in increased __________ when meat is cooled before rigor mortis progresses

A

Toughness

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15
Q

Saturated air has a relative humidity (RH) of __________. Hygroscopic products (e.g., nuts, dried fruits) must be stored at __________ RH

A

100%; low

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16
Q

Fruits and vegetables going into storage are usually contaminated, especially with __________ spores

A

Mold

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17
Q

Define pre-cooling of fruits/vegetables

A

Fast cooldown prior to storage or shipment to decrease temperature rapidly. (e.g., asparagus, snap peas, broccoli, beets, and other leafy vegetables are treated by top ice, ice slush, or cold water after harvest)

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18
Q

The objective of modified atmosphere storage is to ____________________ of fruits and vegetables

A

Decrease respiration rate

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19
Q

Our atmosphere (air) is composed of _____ nitrogen and _____ oxygen, while the remaining 1% is composed or argon, CO2 and other gases

A

78%; 21%

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20
Q

Optimum temperature for home freezing is about __________

A

-18 degrees C

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21
Q

Most raw vegetables can be stored for only a short period of time, even at -20 degrees C due to changes in sensory properties as a result of __________ activity

A

Enzyme

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22
Q

Name the two indicator enzymes for blanching:

A

Catalase and peroxidase

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23
Q

Advantages of blanching:

A

Fix colour, ease of packaging, decrease enzyme activities, decrease microorganisms

24
Q

Disadvantages of blanching:

A

Loss of texture, flavour, nutrients by heating and loss of water-soluble vitamins

25
Q

Some ice crystals are unstable during frozen storage, and they will undergo morphological changes known collectively as __________

A

Recrystallization

26
Q

When food spoil, they become inedible or hazardous to eat because of:

a) Microbial growth
b) Enzymatic action
c) Non-enzymatic action
d) All of the above

A

d) All of the above

27
Q

Microorganisms may play important, advantageous roles in food preservation. Which of the following is not an example of a food where this principle has been applied?

a) Soy sauce
b) Sauerkraut
c) Swiss cheese
d) Low-fat milk

A

d) Low-fat milk

28
Q

When foods are freeze-dried, they are

a) Frozen in liquid nitrogen
b) Frozen and dried in a warm air dryer
c) Blanched, frozen, and heated in a convection oven
d) Frozen and placed in a vacuum chamber

A

d) Frozen and placed in a vacuum chamber

29
Q

Botulism has been associated with ____________________

A

Home canned vegetables

30
Q

For the highest retention of quality in frozen foods, the freezer should be maintained at a temperature no higher than __________

A

-18 degrees C

31
Q

For the highest retention of quality in frozen foods, the freezer should be maintained at a temperature no higher than __________

A

-18 degrees C

32
Q

Pasteurization is a het process applied to certain foods that is designed to destroy all __________ microorganisms

A

Pathogenic

33
Q

In general, before vegetables are frozen, they should be __________

A

Blanched

34
Q

Many frozen fruits require sugar to protect against ____________________

A

Enzymatic actions

35
Q

Name two vegetables that do not freeze satisfactorily

A

Tomatoes, cucumbers

36
Q

Name two fruits that do not freeze satisfactorily

A

Watermelons, apples

37
Q

Unwanted enzyme activity in frozen fruits may be controlled by the addition of ____________________

A

Vitamin C and/or sugar

38
Q

The process of freezing rapidly at a very low temperature is called ____________________

A

Cryogenic freezing

39
Q

What is the minimum recommended temperature for cooking poultry?

A

165 degrees F

40
Q

Potentially hazardous goods generally will have these characteristics

A

High protein foods, high moisture foods, low acid foods

41
Q

“Clean” means that the surface/equipment has been

A

Washed to remove visible soil (does not mean sanitation to kill microorganisms)

42
Q

TRUE or FALSE?
A few hours delay between harvest or slaughter and refrigeration is sufficient to permit marked food deterioration to occur.

A

TRUE

43
Q

TRUE or FALSE?

Pure water will freeze at 0°C, but most foods will not begin to freeze until about -2°C or lower.

A

TRUE

44
Q

TRUE or FALSE?
Most food spoilage microorganisms grow rapidly at temperatures above 10°C, but some grow at temperatures below 0°C as long as there is unfrozen water available

A

TRUE

45
Q

TRUE or FALSE?

Refrigeration and cool storage cause significant adverse effects on the sensory and nutritional properties of foods

A

FALSE

46
Q

TRUE or FALSE?
The principal requirements for effective refrigerated storage are controlled low temperature, air circulation, humidity control, and modification of gas atmospheres.

A

TRUE

47
Q

TRUE or FALSE?

Ultraviolet light cannot be used to retard mold growth and development of surface bacterial slime in aging meat

A

FALSE

48
Q

TRUE or FALSE?
The rate of respiration in fruits and vegetables can be reduced by decreasing temperature, eliminating oxygen, and increasing carbon dioxide

A

FALSE

49
Q

TRUE or FALSE?
Food constituents have different thermal conductivity properties; for example, water has a thermal conductivity far less than that of fat

A

FALSE

50
Q

TRUE or FALSE?

Most foods store best at refrigeration temperatures when the relative humidity of air is between about 60% and 65%.

A

FALSE

51
Q

TRUE or FALSE?
If two food systems both contained 50% fat and 50% moisture, but one was an oil-in-water emulsion and the other was a water-in-oil emulsion, the two foods would be expected to have the same thermal conductivity properties

A

FALSE

52
Q

TRUE or FALSE?

Freeze concentration of solutes can increase the rate of some chemical reactions

A

TRUE

53
Q

TRUE or FALSE?

Refrigerated or frozen storage is appropriate for all types of food products

A

FALSE

54
Q

TRUE or FALSE?
Cryogenic liquids, such as nitrogen and carbon dioxide, are liquefied gases of extremely low boiling points, with boiling points of -79°C and -196°C, respectively

A

FALSE

55
Q

TRUE or FALSE?
Water generally becomes super-cooled to a temperature several degrees below 0°C before some stimulus, such as crystal nucleation, initiates the freezing process

A

TRUE

FN3342 - Advanced Food Science (9 decks)

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