Week12C2

Question 1

What is the moisture sorption isotherm?

Answer 1

evaluation of the water content (%) as a function of the relative humidity of the air. So it is how a food product react to different moisture content in the air.

Question 2

Give the formula that relates the Aw to the RH

Answer 2

Aw = RH/100

Question 3

How do you measure the moisture sorption isotherm?

Answer 3

different salt chambers containing different salts that absorb different levels of moisture with you sample. You weight the salt before and after the experiment and the weight gain represent the moisture absorbed by the salt.

Question 4

What can the moisture sorption isotherm tell you? (5)

Answer 4

1. shows the behavior as a function of RH
2. indicate the effect of temperature on the moisture content (from various graphs)
3. We can know the expected Aw of a product at a specific temperature and RH (stability)
4. Predict the final moisture content
5. indicate the packaging requirements

Question 5

What are the factors affecting the drying process?

Answer 5

1. Pressure (vaccuum) because the boiling point is reduced
2. Latent heat (enthalpy) of evaporation
3. Structure of the product (example layer of fat around)

Question 6

T or F : reducing the pressure means the process of drying will require less temperature difference

Answer 6

t

Question 7

for every ____ ˚C rise in temperature, the air holds twice as much moisture in vapor form

Answer 7

15˚C

Question 8

T or F : faster is the drying better the quality. Hence, the food product should be dried the fastest way possible

Answer 8

false because a hard shell that traps moisture called case hardening can occur if the drying is too fast.

Question 9

T or F : dehydration temperature are not high enough to denature the enzymes so many foods are pretreated to inactivate enzymes

Answer 9

t

Question 10

What are the ways to control the enzymatic activity?

Answer 10

1. pasteurization
2. blanching (water or steam)
3. sulfiting
4. sulfuring

Question 11

What are the ways to control the enzymatic activity by heat?

Answer 11

1. pasteurization

2. blanching (water or steam)

Question 12

What is sulfiting?

Answer 12

soaking food in sodium bisulfite and a water solution for 10 ro 30 minutes to control the enzymatic activity.

Question 13

What are the disadvantages of sulfiting?

Answer 13

1. extend drying time

2. can cause allergic response for people allergic to bisulfite

Question 14

What is the chemical used in sulfiting?

Answer 14

sodium bisulfite

Question 15

What is sulfuring?

Answer 15

exposing the fruits to fumes from burning sulfur up to 4 hours

Question 16

What are the disadvantages of sulfuring and sulfiting?

Answer 16

destroys thiamin

Question 17

What can people be allergic to in the case of :
sulfiting
sulfuring

Answer 17

sulfiting : bisulfate

sulfuring : sulfure dioxide

Question 18

T or F : sulfuring is made from dipping the fruits in a sulfure dioxide solution

Answer 18

true, it can be made that way

Question 19

What is the difference between sulfuring and sulfiting?

Answer 19

sulfuring involves sulfure dioxide and sulfiting involves bisulfate

Question 20

What are the advantages of sulfuring?

Answer 20

1. shortened drying time
2. inhibited mold growth
3. insect repellent

Question 21

Name the various dehydration method seen in class (6)

Answer 21

1. tray drying
2. belt drying
3. drum drying
4. spray drying
5. vacuum drying
6. freeze drying

Question 22

What is the easiest method of all the drying methods?

Answer 22

the tray drying method

Question 23

What is the belt drying method? what is the moisture content you can reach with this method?

Answer 23

food on a tunnel dehydrator. It is a continuous method and can reach a moisture content of 5 to 7%.

Question 24

What is the best drying method for heat resistant food such has potatoes, sweet potatoes and tomato pastes?

Answer 24

drum drying

Question 25

What is the best method for drying liquids?

Answer 25

spray drying.

Question 26

What is the best method for heat sensitive products like milk, eggs, protein powders, flavoring and instant coffee?

Answer 26

spray drying

Question 27

What is the fastest drying method?

Answer 27

spray drying

Question 28

T or F : vacuum drying would be suitable for products that don’t cost a lot of money

Answer 28

false

Question 29

What are the other names of freeze drying ?

Answer 29

lypholization or dehydrofreezing.

Question 30

T or F : freeze drying would be suitable for products that don’t cost a lot of money

Answer 30

false, it is an expensive method

Question 31

What is freeze drying?

Answer 31

freezing food than applying a vaccum so the water can sublimate.

Question 32

T or F : concentration may be the first step to dehydration

Answer 32

true

Question 33

What are the problems with concentrates ?

Answer 33

1. cooked flavors
2. color changes
3. gritty textures
4. denatured proteins

Question 34

What are the 4 concentration methods seen in class

Answer 34

1. open kettle
2. heat evaporation method
3. vacuum evaporation
4. filtration method

Question 35

What is the moisture content of intermediate moisture foods?

Answer 35

20 to 50%

Question 36

T or F : reduction of the water activity is not the only mechanism that explains the preservative effect of concentration

Answer 36

True, because there is also reduction in pH and also increase in the osmotic pressure