Drying And Dehydration

Question 1

Higher drier/dry bulb temperature

Answer 1

Faster drying rate

Question 2

Most expensive and unique drying method

Answer 2

Freeze drying

Question 3

Why do high fat foods have slower drying rate?

Answer 3

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

Question 4

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

Answer 4

Higher drying rate

Question 5

Heat is supplied by convection

Answer 5

Drying using heated air

Question 6

Process of cabinet drying

Answer 6

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

Question 7

Classification of drying processes

Answer 7

Thermal drying
Osmotic drying
Mechanical dewatering

Question 8

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

Answer 8

True.

Question 9

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

Answer 9

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

Question 10

How does drying affect solubility?

Answer 10

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

Question 11

Basic drying methods

Answer 11

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

Question 12

Higher surface temperatures

Answer 12

Faster drying rate

Question 13

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

Answer 13

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

Question 14

Typical solutes used for osmotic drying

Answer 14

Sugar or salt

Question 15

Factors that influence quality during drying include

Answer 15

Chemical
- browning reactions
- lipid oxidation
- color loss

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

Nutritional
- vitamin loss

Question 16

Not a major nutritional loss during drying

Answer 16

Protein loss

Question 17

True or false. You can achieve 100% rehydration.

Answer 17

False

Question 18

Advantages of dehydration

Answer 18

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

Question 19

Follows osmosis, commonly used in fruits

Answer 19

Osmotic drying

Question 20

Maillard browning depends on

Answer 20

Water activity and temperature

Question 21

Sensitive to high temperatures at high moisture content

Answer 21

Vitamin C

Question 22

Associated chemical changes with textural changes

Answer 22

Crystallization of cellulose
Degradation of pectins
Starch gelatinization

Question 23

Why dehydrate food?

Answer 23

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

Question 24

Color changes during browning reactions are affected by

Answer 24

Amount of ingredients
Control of heated air

Question 25

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

Answer 25

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

Question 26

Carotenoid and chlorophyll leads to

Answer 26

Higher drying temperature

Question 27

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

Answer 27

Structural and chemical changes

Question 28

Two types of browning

Answer 28

Enzymatic browning Non-enzymatic browning - caramelization - Maillard reaction

Question 29

Lipid oxidation causes what?

Answer 29

Rancidity Off flavors Loss of fat soluble vitamins and pigments

Question 30

Dehydration

Answer 30

Removal of moisture under controlled conditions.

Question 31

What is the effect of drying on pigments?

Answer 31

Longer drying times cause higher pigment loss.

Question 32

Enzymatic browning is prevented by

Answer 32

Blanching or treatment with sulfur dioxide or ascorbic acid

Question 33

Heat is used to dry the product

Answer 33

Thermal drying

Question 34

Shrinkage reduces

Answer 34

Wettability Product texture Product absorbency

Question 35

More bound water

Answer 35

Slower drying rate

Question 36

Faster moisture loss

Answer 36

Faster drying rate

Question 37

Effect of oxygen on lipid oxidation is closely related to

Answer 37

product porosity

Question 38

Oxidation during storage contributes to increase in ____________ losses.

Answer 38

Organic compounds for aroma and flavor

Question 39

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

Answer 39

Blanching. Opens up spores for moisture to easily escape.

Question 40

More free water

Answer 40

Faster drying rate

Question 41

Mechanism of drying

Answer 41

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

Question 42

Heat supplied mainly by conduction

Answer 42

Drying by direct contact with a heated surface

Question 43

Drying rates of meat depend on

Answer 43

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

Question 44

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

Answer 44

Freeze drying

Question 45

Drying

Answer 45

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

Question 46

Stress cracks are induced by

Answer 46

Uneven volumetric changes resulting in uneven moisture and temperature distribution

Question 47

Higher fat content

Answer 47

Slower drying rate

Question 48

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

Answer 48

Mechanical dewatering

Question 49

Describe the mechanism of drying.

Answer 49

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.

Question 50

Factors affecting the drying rate.

Answer 50

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

Question 51

Osmotic drying makes use of _________ solutions, wherein….

Answer 51

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

Question 52

Temperature of driers

Answer 52

60-70 C

Question 53

Osmotic drying Water: Osmotic substances: Natural solubles:

Answer 53

Exits Enters Exits

Question 54

Maillard reaction

Answer 54

Reducing sugars form a complex with amino acids

Question 55

Higher relative humidity

Answer 55

Slower drying rate

Question 56

Often lost during dehydration; responsible for flavor and aroma

Answer 56

Organic compounds

Question 57

Lower SVR has slower drying rate. Why?

Answer 57

Moisture from interior takes longer to reach the surface.

Question 58

Higher air velocity

Answer 58

Faster drying rate

Question 59

Rehydration is maximized when

Answer 59

cellular and structural disruption are minimized

Question 60

Disadvantage of mechanical dewatering

Answer 60

Liquid/soluble compounds are still present

Question 61

Browning reactions cause

Answer 61

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