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FN 132 - LE #2 > Drying And Dehydration > Flashcards

Drying And Dehydration Flashcards

1
Q

Higher drier/dry bulb temperature

A

Faster drying rate

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2
Q

Most expensive and unique drying method

A

Freeze drying

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3
Q

Why do high fat foods have slower drying rate?

A

Contains less water. Fat, due to its hydrophobic nature, may create a barrier that slows down water migration from interior to surface.

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4
Q

Smaller cubes or those with higher surface-to-volume ratio

A

Higher drying rate

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5
Q

Heat is supplied by convection

A

Drying using heated air

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6
Q

Process of cabinet drying

A

Fresh air is utilized -> moves in the heater making it hot -> fan sweeps away hot air going to the tray -> hot air moves in above & below the trays -> hot air then sweeps moisture becoming humid which contains moisture -> moves out in the exhaust

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7
Q

Classification of drying processes

A

Thermal drying
Osmotic drying
Mechanical dewatering

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8
Q

True or false. Cubes are smaller and with concave surfaces.

A

True.

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9
Q

In drying using heated air, what are the various forms of product chamber?

A

Cabinet dryer - dried mangoes
Tunnel dryer - industrial
Belt dryer
Spray dryer - industrial, powdered milk

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10
Q

How does drying affect solubility?

A

Increase in product temperature —> increase in protein denaturation —> decrease in solubility

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11
Q

Basic drying methods

A

Drying using heated air
Drying by direct contact with a heated surface
Freeze drying

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12
Q

Higher surface temperatures

A

Faster drying rate

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13
Q

Which is more porous? Air-dried or freeze-dried? Why? How does porosity affect lipid oxidation?

A

Freeze-dried. Lack of ice in the matrix —> more porous —> more oxidation

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14
Q

Typical solutes used for osmotic drying

A

Sugar or salt

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15
Q

Factors that influence quality during drying include

A

Chemical
- browning reactions
- lipid oxidation
- color loss

Physical
- rehydration
- aroma loss
- texture
- solubility
- shrinkage

Nutritional
- vitamin loss

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16
Q

Not a major nutritional loss during drying

A

Protein loss

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17
Q

True or false. You can achieve 100% rehydration.

A

False

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18
Q

Advantages of dehydration

A

Generally superior in terms of quality
Sanitary conditions are easily controlled
More expensive but superior quality commands a higher market value
Shorter drying period
Higher yield
Can be done under any weather conditions

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19
Q

Follows osmosis, commonly used in fruits

A

Osmotic drying

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20
Q

Maillard browning depends on

A

Water activity and temperature

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21
Q

Sensitive to high temperatures at high moisture content

A

Vitamin C

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22
Q

Associated chemical changes with textural changes

A

Crystallization of cellulose
Degradation of pectins
Starch gelatinization

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23
Q

Why dehydrate food?

A

Preservation (reduce water activity)
Obtain specific attributes (flavor, texture, etc.)
Reduce bulk and transport costs
Enable formulation of specific products

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24
Q

Color changes during browning reactions are affected by

A

Amount of ingredients
Control of heated air

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25
Q

Why is bound water more difficult to remove during drying? What does it require?

A

Attached to food components and interacts with the molecular structure of food. Requires higher temp or longer time to break bonds

26
Q

Carotenoid and chlorophyll leads to

A

Higher drying temperature

27
Q

The degree to which a dehydrated sample will rehydrate depends on the

A

Structural and chemical changes

28
Q

Two types of browning

A

Enzymatic browning
Non-enzymatic browning
- caramelization
- Maillard reaction

29
Q

Lipid oxidation causes what?

A

Rancidity
Off flavors
Loss of fat soluble vitamins and pigments

30
Q

Dehydration

A

Removal of moisture under controlled conditions.

31
Q

What is the effect of drying on pigments?

A

Longer drying times cause higher pigment loss.

32
Q

Enzymatic browning is prevented by

A

Blanching or treatment with sulfur dioxide or ascorbic acid

33
Q

Heat is used to dry the product

A

Thermal drying

34
Q

Shrinkage reduces

A

Wettability
Product texture
Product absorbency

35
Q

More bound water

A

Slower drying rate

36
Q

Faster moisture loss

A

Faster drying rate

37
Q

Effect of oxygen on lipid oxidation is closely related to

A

product porosity

38
Q

Oxidation during storage contributes to increase in ____________ losses.

A

Organic compounds for aroma and flavor

39
Q

Best method of preparation for vegetables in terms of drying. Why?

A

Blanching. Opens up spores for moisture to easily escape.

40
Q

More free water

A

Faster drying rate

41
Q

Mechanism of drying

A

Simultaneous application of heat and removal of moisture —> dry product

42
Q

Heat supplied mainly by conduction

A

Drying by direct contact with a heated surface

43
Q

Drying rates of meat depend on

A

Fat and lean content
Position of drying air
Arrangement of fat and lean mass

44
Q

Moisture is frozen and then sublimed to vapor by the application of heat at very low pressure

A

Freeze drying

45
Q

Drying

A

Generally applies to all methods of moisture removal; = natural method or sun drying

46
Q

Stress cracks are induced by

A

Uneven volumetric changes resulting in uneven moisture and temperature distribution

47
Q

Higher fat content

A

Slower drying rate

48
Q

Uses a mechanical presser to squeeze out the water from the food

A

Mechanical dewatering

49
Q

Describe the mechanism of drying.

A

Heat penetrates the food’s surface.
Moisture travels up through diffusion or osmosis and reaches the surface.
Dry air sweeps away moisture.
The process continues to reach equilibrium.

50
Q

Factors affecting the drying rate.

A

Properties of the drier
Relative humidity
Air velocity
Dry bulb temperature

Properties of the food
Moisture content
Method of preparation
Rate of moisture loss
Surface-to- volume ratio
Surface temperature
Fat content

51
Q

Osmotic drying makes use of _________ solutions, wherein….

A

Hypertonic, solutes are higher than solvent, water inside the fruit will exit to reach equilibrium

52
Q

Temperature of driers

A

60-70 C

53
Q

Osmotic drying
Water:
Osmotic substances:
Natural solubles:

A

Exits
Enters
Exits

54
Q

Maillard reaction

A

Reducing sugars form a complex with amino acids

55
Q

Higher relative humidity

A

Slower drying rate

56
Q

Often lost during dehydration; responsible for flavor and aroma

A

Organic compounds

57
Q

Lower SVR has slower drying rate. Why?

A

Moisture from interior takes longer to reach the surface.

58
Q

Higher air velocity

A

Faster drying rate

59
Q

Rehydration is maximized when

A

cellular and structural disruption are minimized

60
Q

Disadvantage of mechanical dewatering

A

Liquid/soluble compounds are still present

61
Q

Browning reactions cause

A

Changes in color
Decreased nutritional value and solubility
Off flavors
Textural changes

FN 132 - LE #2 (8 decks)

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