Week12C2 Flashcards
What is the moisture sorption isotherm?
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.
Give the formula that relates the Aw to the RH
Aw = RH/100
How do you measure the moisture sorption isotherm?
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.
What can the moisture sorption isotherm tell you? (5)
- shows the behavior as a function of RH
- indicate the effect of temperature on the moisture content (from various graphs)
- We can know the expected Aw of a product at a specific temperature and RH (stability)
- Predict the final moisture content
- indicate the packaging requirements
What are the factors affecting the drying process?
- Pressure (vaccuum) because the boiling point is reduced
- Latent heat (enthalpy) of evaporation
- Structure of the product (example layer of fat around)
T or F : reducing the pressure means the process of drying will require less temperature difference
t
for every ____ ˚C rise in temperature, the air holds twice as much moisture in vapor form
15˚C
T or F : faster is the drying better the quality. Hence, the food product should be dried the fastest way possible
false because a hard shell that traps moisture called case hardening can occur if the drying is too fast.
T or F : dehydration temperature are not high enough to denature the enzymes so many foods are pretreated to inactivate enzymes
t
What are the ways to control the enzymatic activity?
- pasteurization
- blanching (water or steam)
- sulfiting
- sulfuring
What are the ways to control the enzymatic activity by heat?
- pasteurization
2. blanching (water or steam)
What is sulfiting?
soaking food in sodium bisulfite and a water solution for 10 ro 30 minutes to control the enzymatic activity.
What are the disadvantages of sulfiting?
- extend drying time
2. can cause allergic response for people allergic to bisulfite
What is the chemical used in sulfiting?
sodium bisulfite
What is sulfuring?
exposing the fruits to fumes from burning sulfur up to 4 hours
What are the disadvantages of sulfuring and sulfiting?
destroys thiamin
What can people be allergic to in the case of :
sulfiting
sulfuring
sulfiting : bisulfate
sulfuring : sulfure dioxide
T or F : sulfuring is made from dipping the fruits in a sulfure dioxide solution
true, it can be made that way
What is the difference between sulfuring and sulfiting?
sulfuring involves sulfure dioxide and sulfiting involves bisulfate
What are the advantages of sulfuring?
- shortened drying time
- inhibited mold growth
- insect repellent
Name the various dehydration method seen in class (6)
- tray drying
- belt drying
- drum drying
- spray drying
- vacuum drying
- freeze drying
What is the easiest method of all the drying methods?
the tray drying method
What is the belt drying method? what is the moisture content you can reach with this method?
food on a tunnel dehydrator. It is a continuous method and can reach a moisture content of 5 to 7%.
What is the best drying method for heat resistant food such has potatoes, sweet potatoes and tomato pastes?
drum drying
What is the best method for drying liquids?
spray drying.
What is the best method for heat sensitive products like milk, eggs, protein powders, flavoring and instant coffee?
spray drying
What is the fastest drying method?
spray drying
T or F : vacuum drying would be suitable for products that don’t cost a lot of money
false
What are the other names of freeze drying ?
lypholization or dehydrofreezing.
T or F : freeze drying would be suitable for products that don’t cost a lot of money
false, it is an expensive method
What is freeze drying?
freezing food than applying a vaccum so the water can sublimate.
T or F : concentration may be the first step to dehydration
true
What are the problems with concentrates ?
- cooked flavors
- color changes
- gritty textures
- denatured proteins
What are the 4 concentration methods seen in class
- open kettle
- heat evaporation method
- vacuum evaporation
- filtration method
What is the moisture content of intermediate moisture foods?
20 to 50%
T or F : reduction of the water activity is not the only mechanism that explains the preservative effect of concentration
True, because there is also reduction in pH and also increase in the osmotic pressure
