Water Activity

Question 1

Water Content

Answer 1

How many g water is present in 100g in food and drink

Question 2

Water activity

Answer 2

Water that is not strongly bound to other molecules

Determines food properties

Question 3

Properties of water

Answer 3

Polar
Adhesion and cohesion
Binds to hydrophilic molecules
Causes phase seperation

Question 4

Adhesion and cohesion

Answer 4

Surface tension

Capillary tube action - means hard to remove water from pores as acts against gravity

Question 5

Phase seperation

Answer 5

Hydrophobic molecules are separated from water and squeezed out

Question 6

Water activity

Answer 6

Amount of water available to form new hydrogen bonds

Pure water has an aw of 1.0
No available water is 0.0

Question 7

Drying

Answer 7

Removing water lowering the water activity

Question 8

Freezing

Answer 8

Reduces water that is available as frozen crystals are not available to form hydrogen bonds

Question 9

Spoilage and water activity

Answer 9

Growth of microorganism

Only occur above certain water activity

Question 10

Vapour Pressure

Answer 10

At any temperature there will be some molecules that have vaporised.
Water leaves water pool enter vacuum
H2O in vacuum enters water pool
Equilibrium does reach

Question 11

Vapour pressure and solutes

Answer 11

Dissolved molecules reduce vapour pressure
Proportional to number of dissolved molecules
Not relevant to size

Hence why large molecules do not affect water as much as small in same concentration

Question 12

Vapour pressure and salt reduction

Answer 12

Relevant to food as reduction of salt increases water activity

Question 13

Vapour pressure and water activity

Answer 13

Relative vapour pressure = Vapour pressure / Vapour pressure pure water = Water activity
Chemical and enzymic reactions related to RVP

Question 14

Relative humidity %

Answer 14

Relative Vapour Pressure x 100

Question 15

Properties of Ice

Answer 15

Ice is lighter than water as H2O molecules not random so less packed

Question 16

Freezing principle

Answer 16

Slowing the moving particles binding to ice crystals and then increase crystal size.

When an atom stops moving it gives of energy raising the temperature of the body temperature

Therefore while both ice and water are present temperature remains stable

Question 17

Freezing with solvent

Answer 17

Solvent lowers freezing point

This is as crystal matrix does not hav space for other molecules in it

Also means section become ice first will not be as concentrated as liquid

Question 18

Delete

Answer 18

Delete

Question 19

Delete

Answer 19

Delete