Water Flashcards
Which equation is used to determine water density?
Density= mass/ volume
What is the reason for the high surface tension of water?
The hydrogen bonding
What type of bonds are present in water?
Covalent bonding- O and H
- 2S and 2P sub shells hydrides to form four 2SP3 orbitals
Outline the relation between food stability and water.
If there is a high water content in foods, these foods will spoil more quickly
What methods can be used to inhibit food deterioration?
We can inhibit food deterioration but reducing the availability of water, this is done by freezing, drying and adding salt or sugar.
Which equation is used to determine water activity?
aw = P/P0
aw = water activity P = partial pressure of water above the material P0 = partial pressure of pure water at the same temperature
How is Equilibrium relative humidity (ERH) expressed?
Equilibrium relative humidity is water activity expressed as a percentage; ERH = aw x 100
What variable can we increase to increase water activity?
Temperature can be increased to increase water activity.
What are the four ‘levels’ of water?
Vicinal
Bound
Entrapped
Free
What are the key features of vicinal water?
Strongly bound Hard to remove with heat Does not freeze Not a solvent aw= 0.25
What are the key features of bound water?
Freezes at -40 degrees
1-5% of the water in high moisture food
aw= 0.8
What are the key features of entrapped water?
Water that is being physically held by tissues
96% of the water in high moisture food
What are the key features of free water?
Has normal solvent capacity and freezing point96% of the water in high moisture food
What is the name of the law that can be used to estimate water activity?
Raoult’s Law
What is the equation of Raoult’s Law?
aw = nw / (ns + nw)
What does this refer to: ‘a law stating that the vapour pressure of an ideal solution is proportional to the mole fraction of solvent’?
Raoult’s Law
What two minerals does hard water contain?
Hard water contains dissolved magnesium and calcium ions
What causes temporary hardness (water)?
Temporary hardness is caused by dissolved calcium hydrogencarbonate
What causes permanent hardness (water)?
Permanent hardness is caused by dissolved calcium sulfate
How can temporary hardness resolved?
Dissolved calcium hydrogencarbonate can be removed by boiling
Can permanent hardness be resolved?
No it is permanent- dissolved calcium sulfate cannot be removed by boiling
What may be the consequence of a dry atmosphere on food?
It will cause a loss of water and therefore dried out food e.g. stale food
What may be the consequence of a moist atmosphere on food?
It will cause a gain of water and therefore ‘sticky’ food e.g. sugar clumps
Give an example of a water borne pathogen that is spread through faecal contamination
Salmonella
Define enteric virus
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.
Give an example of an enteric virus that is spread through a contaminated water supply
Hepatitis A
Give an example of a disease that is spread through parasites stemming from a contaminated water supply
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.
Give two methods for softening water
Ion-exchange resin method.
Lime softening.
Define biological oxygen demand (BOD)
The amount of dissolved oxygen used by microorganisms in the biological process of metabolising organic matter in water.
Define chemical oxygen demand (COD)
Chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution
What are BOD and COD used for?
To assess the effect discharged wastewater will have on the receiving environment
Outline the method of sewage treatment
Sewage is screened at the source, moved into settlement tanks, undergoes aeration, allowed to settle, undergoes filtration and then released into rivers
Which illnesses can result from produce contamination?
Norovirus, Salmonella, Listeria
What are the sources of produce contamination?
Poor farm worker hygiene, manure overflow, contaminated water or flooding
What is the legal limit for chlorine washing fruit and salad in the UK?
50-200ppm, for a short amount of contact time
Outline the method of water treatment
Water is screened at the source, put through a flash mixer, undergoes flocculation, sand filtration and then chlorination
What is the equation used to establish the percentage of water on a dry weight basis?
Percentage of water (dry)= mass loss/ food mass after drying x 100
What is the equation used to establish the percentage of water on a fresh weight basis?
Percentage of water (fresh)= mass loss/ original food mass x 100
Outline the method used to determine water content
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
