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Nutrition > Water in Food > Flashcards

Water in Food Flashcards

1
Q

What is the equation for density?

A

Mass / Volume

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2
Q

What are the properties of water?

A

Large surface tension
High heat capacity
High latent heat of vaporisation
High dielectric constant

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3
Q

What is dielectric constant?

A

The relative amount of electrical energy stored in a material vs the amount of electrical energy of free space

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4
Q

What bonding occurs in water?

A 
Covalent = between oxygen and hydrogen within a water molecule 
Hydrogen = between hydrogen and oxygens of different water molecules
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5
Q

How can you determine the water content of a food?

A
  1. Weigh dry container
  2. Weigh sample in the dry container after grinding
  3. Heat at a specified temperature
  4. Weigh sample
  5. Repeat heating and weigh process until a constant mass is obtained
  6. Calculate the mass loss
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6
Q

What are the disadvantages of determining the water content of food by heating and weighing?

A

Mass loss varies with heating conditions
There may be loss of substances other than water
There may be an incomplete removal of bonded water within the food

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7
Q

What is the calculation for percentage of water of a food on a fresh weight basis?

A

(Mass loss / Original food mass) x 100

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8
Q

What is the calculation for percentage of water of a food on a dry weight basis?

A

(Mass loss / Food mass after drying) x 100

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9
Q

Do foods with a high water content spoil more or less easily than foods with a lower water content?

A

More easily

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10
Q

How can foods with a high water content be prevented from spoiling?

A

By making water unavailable

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11
Q

How is water made unavailable in foods with a high water content?

A

Remove water = drying or concentrating

Immobilise water = freezing, adding salt, adding sugar

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12
Q

What are the properties of strongly bonded water?

A 
Low water activity 
Does not move easily 
Does not freeze
Does not act as a solvent 
Cannot partake in spoilage reactions 
Low vapour pressure
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13
Q

What is the equation of water activity?

A

p / po
p = vapour pressure of water in equilibrium with sample
po = vapour pressure of pure water at the same temperature

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14
Q

How is equilibrium relative humidity calculated?

A

Aw x 100

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15
Q

How is water in food categorised?

A

Depending on the strength of its bonding

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16
Q

What are the four layers of water found in food?

A

Free / bulk water
Entrapped water
Bound water
Vicinal water

17
Q

How does water activity change as temperature increases?

A

Increases

18
Q

Water moves from regions of _______ water activity to regions of _______ water activity

A

High

Low

19
Q

What are the properties of vicinal water?

A

Most strongly bonded
Removal by heat is difficult and non-reversible
Does not freeze
Does not act as a solvent

20
Q

What is the estimated water acitivty of vicinal water?

A

0.25

21
Q

What are the properties of bound water?

A

Layers are bound by hydrogen bonds

Water is held in capillaries

22
Q

What is the estimated water activity of bound water?

A

0.8

23
Q

What are the properties of entrapped water?

A

Water is held in tissue matrix (behind membranes of in capillaries) which prevents flow
Lower freezing point than free water
More likely to act as a solvent compared to bound water

24
Q

What are the properties of free / bulk water?

A

Behaves like pure water

Readily squeezed out by pressure

25
Q

What happens to a food when the water activity of the food is greater than the water activity of the atmosphere?

A

Food loses water

26
Q

What happens to a food when the water activity of the food is less than the water activity of the atmosphere?

A

Food gains water

27
Q

Does water movement occur between foods that are in contact with each other?

A

Yes

28
Q

What is Raoults law?

A

Water activity = Nw / (Ns + Nw)
Nw = moles of solvent
Ns = moles of solute

Nutrition (27 decks)

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