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Nutrition Semester 1 > BMS1064: Wk2 - Water > Flashcards

BMS1064: Wk2 - Water Flashcards

1
Q

How do you calculate density?

A

Density = Mass/Volume

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2
Q

At what temp is water most dense?
Whats unusual about water?

A

Around 4 degrees C.

It expands when freezing (less dense as solid).

SO water at 4C is at bottom of lake with ice floating on top.

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3
Q

Water has an unusually great: (what 5 things?)

A
  • Density
  • Surface tension
  • Dielectric Constant
  • Heat Capacity (energy to raise by 1 degree)
  • Latent Heat Capacity (energy to convert liquid to gas without temp change)
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4
Q

Which are stronger? Hydrogen or Covalent bonds?

A

Covalent (Intramolecular)

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5
Q

How do you determine the water content of a sample?

A
  1. Weigh dry container
  2. Grind food, add to container and weight container again (with sample)
  3. Heat at specified temp for specified time
  4. Weigh sample again
  5. Reheat untul constant mass
  6. Calculate mass lossW
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6
Q

When determining water content of a sample, what could cause variations in mass loss?

A

Incomplete removal of ‘bound’ water molecules.
Loss of substances other than water.

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7
Q

What is the equation to calculate % of water in a sample on a FRESH WEIGHT basis?

A

% water = (Mass loss / original food mass) x 100

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8
Q

What is the equation to calculate % of water in a sample on a DRY WEIGHT basis?

A

% water = (Mass loss / food mass after drying) x 100

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9
Q

When answering Qs where you need to calculate things, how should you answer?

A

Write out equation
Identify components in Q
Put numbers into equation
Calculate answer

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10
Q

How can you increase the shelf-life of food in relation to water and why would you do this?

A

Remove water (by drying or concentrating) or Immobilise water (by freezing or adding sugar - unavailable for reactions).

Food with high water content spoil more rapidly.

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11
Q

What is Water Activity?

A

How ‘available’ water is to take place in chemical reactions.
aw is an average for all the water in the food.

More strongly bound water has lower Water Activity.

Water Activity is more important than just the water content of food.

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12
Q

What can strongly bound water not do?

A
  • Does not move easily within a food.
  • Does not freeze (cannot move to form ice crystals).
  • Does not act as a solvent - i.e. dissolve substances.
  • Is not available to take part in spoilage reactions.
  • Does not escape easily into the atmosphere (low vapour pressure).
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13
Q

What is Vapour Pressure?

A

The tendency of molecules to escape from a liquid (i.e. evaporate)

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14
Q

What is the equation for Water Activity?

A

aw = p / p0

Water Activity = vapour pressure of water in equilibrium with sample / vapour pressure of pure water at the same temperature

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15
Q

How can you calculate Equilibrium Relative Humidity from Water Activity?

A

aw x 100 = Equilibrium Relative Humidity (ERH %)

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16
Q

What are the catagories that water can be divided into based on the strength of its binding?

A

*Free/bulk water
*Entrapped water
*Bound/multilayer water
*Vicinal water (closest to food surface)

17
Q

How does aw change with temp?

And how does water move according to aw?

A

aw increases with increasing temperature.

Water moves from regions of high aw to regions of lower aw.

18
Q

Describe Vicinal/monolayer water.

A

Found closest to the food surface.

Most strongly bound - removal by heat difficult, does not freeze, not a solvent.

Associated with proteins, polysaccharides and salts.

Present at 0.5 ±0.4% of total water in high moisture food.
The layer of water is complete at aw approx 0.25.

19
Q

Describe bound/multilayer water.

A
  • Successive layers of water bound by hydrogen bonding.
  • Strength of binding declines progressively.
    *Water held in smaller capillaries <1 μm diameter
    *Does not freeze until < -40C
  • 3 ±2% of water of typical high moisture food.
    *Layers complete at awabout 0.8
20
Q

Describe entrapped water.

A

Water physically held/entrapped in the food matrix:
- behind membranes, in capillaries > 1 μm diameter
- prevented from flowing freely by gel structure

Solvent capacity, freezing point, water mobility all slightly less than free water
- Can move short distances

*Up to 96% of total water of a typical high moisture food

21
Q

Describe Free/bulk Water

A

Behaves like pure water.

Held within structure, but readily squeezed out by pressure.
Solvent capacity and freezing point are normal.

  • Up to 96% of total water of a typical high moisture food
22
Q

What causes transfer of water in food?

A

If atmosphere and food have same aw - no water movement.

If aw(food) > aw(atmosphere) then the food loses water.

If aw(food) < aw(atmosphere) then the food gains water

  • Also applies to foods in contact with each other e.g. cucumber sandwiches
23
Q

How do you calculate water activity using moles of solvent and solute?

A

aw = mol of solvent (water) / (mol of solute + mol of solvent)

aw= nw/(ns + nw)

24
Q

What are the units for aw? What is the largest number it can be?

A

No units for aw!

aw will always be <1.

25
Q

Hard -> soft water.

What can be removed by boiling?
What cannot be removed?

A

Temporary hardness - bicarbonates removed by boiling.

Permanent hardness - sulphates and chlorides

26
Q

What are 2 methods of water softening?

A

LIME SOFTENING = addition of Ca(OH)2 and Na2CO2. Calcium and Magnesium ppts.

ION EXCHANGE CARTRIDGES
Resins in cartidges have Na+ ions tompararily associated.
Hard water passes through and Ca2+ and Mg2+ exchange with Na+.
Na+ leaves and becomes NaCl.

27
Q

Name some baecal bacteria that can be found in water.

A

Salmonella
VTEC
Shigella
Vibrio cholerae
Campylobacter

28
Q

Name some Viruses that can be found in water.

A

Hepatitis.
Norovirus.

29
Q

Name some parasites that can be found in water.

A

Cryptosporidium
Cyclospora

30
Q

Give the whole process (including 3 steps) of Portable water treatment.

A

Water screened to remove large particles.
Aeration to remove CO2 etc
Flash mixer - mixed with aluminum suphate (helps form sludge).

1) Flocculation tank - floc (sludge) settles out.
2) Slow or rapid sand filtration
–> ozone, activated carbon and pH control –>
3) Chlorination kills microorganisms
–> UV disinfection —> tap water

31
Q

What is used instead of chlorine gas in chlorination of water?

How is this made safe when using to wash fruit/ev?

A

NH2Cl (Chloramine) + HOCl (Hypochlorus acid)

HOCl inactivated by organic matter when washing fruit/veg.
Short contact time.
Resistance to chlorine varies - 99% reduction

32
Q

Name some common contaminants of food produce (think bacteria/virus/pathogens)

A

Norovirus
Salmonella
Cyclospora
Listeria

33
Q

Name some sources of contamination of food produce.

A

Farm worker hygiene
Manure
Unsanitary conditions on farm processing
Contaminated irrigation water/flooding

34
Q

Describe the whole process of Sewage/Effluent Treatment (inlcudes 4 steps).

A

Sewage screened to remove large particles.

1) Settlement tank to sediment organic solid matter.

2) Aeration - good bacteria consume bad bactera

3) Final settlement of organic matter.

4) Sand filtration

(Sludge burned, anaerobically digested or used as fertiliser)

35
Q

Water pollution testing: Describe the test for Biochemical Oxidation Demand (BOD).

A

Add waste sample to aerated water.
Incubate at 20 degrees C for 5 days.
Measure oxygen used (in mg/L or ppm).

Properly treated effluent should be < 20 mg/L (sewage = 600 mg/L)

36
Q

Water pollution testing: Describe the test for Chemical Oxidation Demand (COD).

A

Add waste sample to boiling dichromate solution.
Measure oxygen used (in mg/L or ppm).

Properly treated effluent should be 200-1000 mg/L.

37
Q

How do we use aerobic oxidation to reduce the BOD value?

A

Organic compound + O2 + minerals + biomass –> CO2 + H2O + more biomass + heat

38
Q

How do we use anaerobic digestion to reduce the BOD value?

  • used more often where there are heavy contaminant
A

Organic compound + minerals + biomass –> CO2 + CH4 + H2O + more biomass + heat

difference = no O2 reactant, extra CH4 product

Nutrition Semester 1 (11 decks)

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