Water

Question 1

Which equation is used to determine water density?

Answer 1

Density= mass/ volume

Question 2

What is the reason for the high surface tension of water?

Answer 2

The hydrogen bonding

Question 3

What type of bonds are present in water?

Answer 3

Covalent bonding- O and H

- 2S and 2P sub shells hydrides to form four 2SP3 orbitals

Question 4

Outline the relation between food stability and water.

Answer 4

If there is a high water content in foods, these foods will spoil more quickly

Question 5

What methods can be used to inhibit food deterioration?

Answer 5

We can inhibit food deterioration but reducing the availability of water, this is done by freezing, drying and adding salt or sugar.

Question 6

Which equation is used to determine water activity?

Answer 6

aw = P/P0

aw = water activity
P = partial pressure of water above the material
P0 = partial pressure of pure water at the same temperature

Question 7

How is Equilibrium relative humidity (ERH) expressed?

Answer 7

Equilibrium relative humidity is water activity expressed as a percentage; ERH = aw x 100

Question 8

What variable can we increase to increase water activity?

Answer 8

Temperature can be increased to increase water activity.

Question 9

What are the four ‘levels’ of water?

Answer 9

Vicinal
Bound
Entrapped
Free

Question 10

What are the key features of vicinal water?

Answer 10

Strongly bound
Hard to remove with heat
Does not freeze
Not a solvent
aw= 0.25

Question 11

What are the key features of bound water?

Answer 11

Freezes at -40 degrees
1-5% of the water in high moisture food
aw= 0.8

Question 12

What are the key features of entrapped water?

Answer 12

Water that is being physically held by tissues

96% of the water in high moisture food

Question 13

What are the key features of free water?

Answer 13

Has normal solvent capacity and freezing point96% of the water in high moisture food

Question 14

What is the name of the law that can be used to estimate water activity?

Answer 14

Raoult’s Law

Question 15

What is the equation of Raoult’s Law?

Answer 15

aw = nw / (ns + nw)

Question 16

What does this refer to: ‘a law stating that the vapour pressure of an ideal solution is proportional to the mole fraction of solvent’?

Answer 16

Raoult’s Law

Question 17

What two minerals does hard water contain?

Answer 17

Hard water contains dissolved magnesium and calcium ions

Question 18

What causes temporary hardness (water)?

Answer 18

Temporary hardness is caused by dissolved calcium hydrogencarbonate

Question 19

What causes permanent hardness (water)?

Answer 19

Permanent hardness is caused by dissolved calcium sulfate

Question 20

How can temporary hardness resolved?

Answer 20

Dissolved calcium hydrogencarbonate can be removed by boiling

Question 21

Can permanent hardness be resolved?

Answer 21

No it is permanent- dissolved calcium sulfate cannot be removed by boiling

Question 22

What may be the consequence of a dry atmosphere on food?

Answer 22

It will cause a loss of water and therefore dried out food e.g. stale food

Question 23

What may be the consequence of a moist atmosphere on food?

Answer 23

It will cause a gain of water and therefore ‘sticky’ food e.g. sugar clumps

Question 24

Give an example of a water borne pathogen that is spread through faecal contamination

Answer 24

Salmonella

Question 25

Define enteric virus

Answer 25

The term 'enteric virus' refers to an important, but diverse, group of viruses found in the intestinal tract of humans and animals. Enteric viruses may also be present in contaminated water supplies and waterborne outbreaks of disease are not uncommon.

Question 26

Give an example of an enteric virus that is spread through a contaminated water supply

Answer 26

Hepatitis A

Question 27

Give an example of a disease that is spread through parasites stemming from a contaminated water supply

Answer 27

Cyclospora - an infection of the bowel caused by a tiny parasite called Cyclospora cayetanensis. It's usually caught from eating raw fruit and vegetables contaminated with human faeces (poo). Diarrhoea, which can often be severe, is the most common symptom of cyclospora.

Question 28

Give two methods for softening water

Answer 28

Ion-exchange resin method. | Lime softening.

Question 29

Define biological oxygen demand (BOD)

Answer 29

The amount of dissolved oxygen used by microorganisms in the biological process of metabolising organic matter in water.

Question 30

Define chemical oxygen demand (COD)

Answer 30

Chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution

Question 31

What are BOD and COD used for?

Answer 31

To assess the effect discharged wastewater will have on the receiving environment

Question 32

Outline the method of sewage treatment

Answer 32

Sewage is screened at the source, moved into settlement tanks, undergoes aeration, allowed to settle, undergoes filtration and then released into rivers

Question 33

Which illnesses can result from produce contamination?

Answer 33

Norovirus, Salmonella, Listeria

Question 34

What are the sources of produce contamination?

Answer 34

Poor farm worker hygiene, manure overflow, contaminated water or flooding

Question 35

What is the legal limit for chlorine washing fruit and salad in the UK?

Answer 35

50-200ppm, for a short amount of contact time

Question 36

Outline the method of water treatment

Answer 36

Water is screened at the source, put through a flash mixer, undergoes flocculation, sand filtration and then chlorination

Question 37

What is the equation used to establish the percentage of water on a dry weight basis?

Answer 37

Percentage of water (dry)= mass loss/ food mass after drying x 100

Question 38

What is the equation used to establish the percentage of water on a fresh weight basis?

Answer 38

Percentage of water (fresh)= mass loss/ original food mass x 100

Question 39

Outline the method used to determine water content

Answer 39

``` Weigh dry container Record weight Grind foodstuff Add sample to the container Weigh and record weight Heat or freeze dry Weigh and record weight Repeat above process until a constant mass is reached Calculate the mass loss ```