Soaking Flashcards
(25 cards)
How to control water content
- Water removal
- add aw lowering solute
- Water phase change (e.g freezing, drying, frying)
What is osmotic dehydration?
Process of water removal by immersion of water by adding food to concentrated aqueous solution of high osmotic
pressure.
What does solution of high osmotic pressure mean?
Solution with many solute particles. High concentration which wants to move to a low concentration.
Chain contraction explain
When polymer contracts and forms rigid structure which lead to phase sepration
Chain expansion
When polymer expands due to electrostatic repulsions, steric hindrance etc.
Give examples of compounds/soluted used for osmotic pressure
- Calcium chloride -> increases firmness and preserves texture during storage.
- Ethanol -> decreases freezing point
Banana candied dried vs frying banana explain how the first is obtained.
Candied dried banana -> sugar solution, insert banana, sugar enters banana, water exits banana,
After osmotic dehydration is the product dry?
No, an air-drying step is added.
What is the type of mass transfer during osmotic dehydration
isothermal -> temperature remains constant
What is the driving force of osmotic drying
the change in viscosity as water is coming out
What are advantages and disadvantages of osmotic drying
Advantages:
1. mild treatment
2. less energy
3. less water at dryer as some already removed
4. simple equipment and low cost
Disadvantages
1. reduction of acidity of fruits
2. modification of original product composition
What are factors affecting osmotic dehydration process?
- Size and Shape
- Concentration of osmotic solution
- Product characteristics: specie, maturity, tissue location etc
- Sample to solution ratio -> (e.g small apple and many liters of solution)
How can the mass transfer in osmotic dehydration be enhanced?
- Centrifugal force
- Vacuum
- Process duration and time
and others
How does vacuum increase mass transfer?
It create pores in the fruits which increase the exchange surface.
How to freeze quickly a product? And what are the driving forces
Put in contact with solution with solutes which allow to decrease freezing point and thus present the solution at 0 to -40 C. The solutes enter the food product and freeze the food.
The driving forces are the change in viscosity and change in temperature.
Does salt mass transfer increase or decrease the freezing point?
Decrease! Water is coming out so i believe that for most of solutes going in the freezing point is decreased.
Does fast freezing lead to small or large crystals? Over time what happens to this crystals?
Fast freezing leads to small crystals, over time this crystals will come together to form larger ones.
What are the benefits of frying at atmospheric pressure?
- “LOW COST” TECHNOLOGY
- BATCH/CONTINUOUS
- HIGH PRODUCTION YIELDS
- COMPACT PROCESS
- ALL IN “ONE” PROCESS
What is the driving force in frying?
Change of temperature.
What is the bump (increase then decrease and then gradual increase) in slide 67 of the temperature over time in frying
a change in local pressure.
What happens during the cooling stage after frying?
Oil fills the volume freed (made free) by the water leaving. During frying liquid and steam exit with force. During cooling suction mechanism occurs where oil penetrates the product
What are some of the benefits of frying?
- Color
- Aroma
- Increase digestibility and starch gelatinized.
Which water is removed: bound or free water? during drying and other processes
free water
What does the water mediated phenomena depend on?
- Type of water removed: free or bound
- Way water migrates
- Rate of water removal
