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Food Science and Nutrition > Water > Flashcards

Water Flashcards

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1
Q

Which equation is used to determine water density?

A

Density= mass/ volume

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2
Q

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

A

The hydrogen bonding

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3
Q

What type of bonds are present in water?

A

Covalent bonding- O and H

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

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4
Q

Outline the relation between food stability and water.

A

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

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5
Q

What methods can be used to inhibit food deterioration?

A

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

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6
Q

Which equation is used to determine water activity?

A

aw = P/P0

aw = water activity
P = partial pressure of water above the material
P0 = partial pressure of pure water at the same temperature
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7
Q

How is Equilibrium relative humidity (ERH) expressed?

A

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

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8
Q

What variable can we increase to increase water activity?

A

Temperature can be increased to increase water activity.

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9
Q

What are the four ‘levels’ of water?

A

Vicinal
Bound
Entrapped
Free

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10
Q

What are the key features of vicinal water?

A 
Strongly bound
Hard to remove with heat
Does not freeze
Not a solvent
aw= 0.25
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11
Q

What are the key features of bound water?

A

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

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12
Q

What are the key features of entrapped water?

A

Water that is being physically held by tissues

96% of the water in high moisture food

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13
Q

What are the key features of free water?

A

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

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14
Q

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

A

Raoult’s Law

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15
Q

What is the equation of Raoult’s Law?

A

aw = nw / (ns + nw)

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16
Q

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

A

Raoult’s Law

17
Q

What two minerals does hard water contain?

A

Hard water contains dissolved magnesium and calcium ions

18
Q

What causes temporary hardness (water)?

A

Temporary hardness is caused by dissolved calcium hydrogencarbonate

19
Q

What causes permanent hardness (water)?

A

Permanent hardness is caused by dissolved calcium sulfate

20
Q

How can temporary hardness resolved?

A

Dissolved calcium hydrogencarbonate can be removed by boiling

21
Q

Can permanent hardness be resolved?

A

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

22
Q

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

A

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

23
Q

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

A

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

24
Q

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

A

Salmonella

25
Q

Define enteric virus

A

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.

26
Q

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

A

Hepatitis A

27
Q

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

A

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.

28
Q

Give two methods for softening water

A

Ion-exchange resin method.

Lime softening.

29
Q

Define biological oxygen demand (BOD)

A

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

30
Q

Define chemical oxygen demand (COD)

A

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

31
Q

What are BOD and COD used for?

A

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

32
Q

Outline the method of sewage treatment

A

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

33
Q

Which illnesses can result from produce contamination?

A

Norovirus, Salmonella, Listeria

34
Q

What are the sources of produce contamination?

A

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

35
Q

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

A

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

36
Q

Outline the method of water treatment

A

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

37
Q

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

A

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

38
Q

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

A

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

39
Q

Outline the method used to determine water content

A 
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

Food Science and Nutrition (28 decks)

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