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5) FDSC 300 > Lecture 4/5- Moisture Analysis > Flashcards

Lecture 4/5- Moisture Analysis Flashcards

1
Q

What are the compoenents of Proximate analysis?

A
  1. Moisture
  2. Ash
  3. Protein
  4. Fibre
  5. Fat
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2
Q

What does water allow?

A

Stucture
Indentity
Cheap filler

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3
Q

What is dry matter?

A

Often the expensive prt
Define nutritional part
Convinient for transport

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4
Q

Why is moisture determination important?

A 
Food safety
Shelf life
Food quality
Economic considerations
Government regulation
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5
Q

What are the 4 forms of water in food?

A

Free
Capillary/trapped
Physically bound
Chemically bound

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6
Q

Characteristics of free water

A

Free from other constituents
Surrounded by other water constituents
Physiochemical same aspure water

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7
Q

Waht are the characteristics of capillary water?

A

WAter is held in narrow channels fromed by physical barriers by capillary forces
–> physiochemical like bulk water

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8
Q

What are the characteristics of physically bound water

A

Water is bound with other molecules (Proteins, Polysaccharides)

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9
Q

What are the characteristics of chemically bound water?

A

WAter is bound chemically (lactose monohydrate, salts)

Different physiochemical properties tob bulk water

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10
Q

What are the methods for moisture measurement?

A
  1. Drying methods
  2. Distillation methods
  3. Chemical methods
  4. Physical methods
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11
Q

What happens with drying methods?

A

Deal with removal of water in the form of vapour and the loss of weight is taken as a measure of the moisture content

  • indirect
  • less specific to water
  • simple
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12
Q

What are some drying methods?

A
  1. Oven drying
  2. Freeze drying
  3. Infrared drying
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13
Q

What is Raoult’s Law?

A

The boiling point of water increases 0.512C for every 1 mol os solute dissolved in 1L of water

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14
Q

What is moisture loss a function of?

A

Time and temperature

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15
Q

At what temp does protein decomposition occur?

A

185C

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16
Q

What happens with carbs break down?

A

at higher temperature and release water

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17
Q

What could increase the weight of the sample during drying?

A

Oxidation of fatty acids

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18
Q

Convection oven

A

As heating takes place, water is lost a sample and moisture remains in teh chanber (105-110)

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19
Q

What are the disadvantages of drying methods

A

Longer analysis time
Loss of volatile components other than water
Larger temperature gradient

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20
Q

What is a forced air oven

A

Air is circulated by a fan

T can be higher and time can be shorter

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21
Q

What are the advantages to a forced air oven

A

Faster, efficient and water vapour will not condense to the fan

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22
Q

Microwave analyzer

A

Microwave drying is rapid technique

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23
Q

How do you make a microwave analyzer accurate?

A

microwave energy and time need to be defined

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24
Q

Vacuum Oven

A

The boiling point of substance is the temperature at whcih the vapor pressure of the liquid equals the pressure surroundin the liquid

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25
Q

What are the adavantages of the vacuum oven?

A

Drying under reduced pressure
Faster rate of evaporation
Removal of water with out decmposition

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26
Q

What is the vacuum overn based on?

A

The fact than water boils at lower T under vacuum

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27
Q

What is the purpose of the vacuum pump?

A

Reduce the ovens pressure to between 25-50mmHg

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28
Q

What are some common drying agents for vacuum ovens?

A

Anhydroud CaCl2
Anhydrous SO3
Phosphorous Pentaoxide P2O5
Concentrated H2SO4

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29
Q

What are the advantages of vacuum drying?

A
  • Reduced Temp
    2- Reduction of loss volatiles
    3- Less effect on degradation of some components
    4- Shorten analysis time
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30
Q

What are factors that affect oven drying?

A

Temperature
Time
PArticle size

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31
Q

What is infra red drying

A

Penetrating infrared rays dry sample
Shorten drying time to 10-25mins
Heat of lamp is 1730-2230C

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32
Q

Is infrared drying approved by AOAC?

A

No

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33
Q

What is distillation

A

Recovery of water via distillation process, then the measurement of the volume of water

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34
Q

What is removed via distillation

A

H2O

When the vapour is cooled

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35
Q

What should a distillation solvent be like?

A

stable and used as a heat transfer media

36
Q

What are the 2 version of distillation solvents?

A
  1. Immiscible/ non volatile ex mineral oil

2. Immiscible/volatile liquid ex toluene

37
Q

What is the direct method of moisture determination

A

Water is removed quickly because of faster heat transfer –> may be less decomposition

38
Q

Is the distillation method an AOAC approved technique?

A

YES

39
Q

What is the other distiallation method?

A

Reflux distillation

40
Q

What are the two solvents to distillation?

A

Mineral oil

Toluene

41
Q

Mineral oil

A

immiscible in water
Volatile
Boiling point 200-310C
Density 0.8g/mL

42
Q

Toluene

A 
Immiscible with water
Volatile
Boiling point 110.6C
Density 0.87g/mL
flammable
43
Q

Two other solvents?

A

Xylen and Tetrachlorethylene

44
Q

Is it better to use volatile liquid or non volatile liquid?

A

Volatile, more effective

45
Q

Toluene distillation

A

Toluene and water will be collected in the receiving trap but will not mix
Water is heavier so the lower layer is measured

46
Q

What are the disadvantages of distillation?

A

Meniscus layer can be hard to read
Toluene is aromatic hydrocarbon ( health and enviromental hazard + flammable
It is not adaptable to routine, fast testing
Possibility of carbohydrate decomposition or maillard reaction

47
Q

What is a Karl-Fisher Titration?

A

Adapted to food products that show erratic results when heated or submitted to a vacuum

48
Q

What is the advantages of the Karl Fisher Titration

A

More specific for H20 than oven drying and distillation
Both free and bound H2O can be determined
Fast
Selective for water
Accurate and precise

49
Q

What can you measure the Karl Fischer with?

A

ppm to %

50
Q

What are the application of the Karls Fischer Method

A

Used in low and very low moisture foods (dehydrated veggies, spices, chocolate
Also in non food applcations

51
Q

what is the Karl Fischer based on?

A

Bunsen Reaction

2H2O+SO2+I2———->H2SO4+2HI

52
Q

What does a bunsen reaction need?

A

Non-aq solvent (benzene- give erradic results, meth and pyridine(non aq base)

53
Q

what is the best titrant ratio

A

Practically, a methanol Karl Fisher solution is used as the titrant
containing Iodine : SO2 : Pyridine at a ratio of 1:3:10 (v/v/v).

54
Q

what are the ingredients of KF reagents?

A

Iodine: I2 (react with water and get converted to
iodide)
Sulfur dioxide: SO2 (to produce sulfuric acid)
Pyridine: C5H5N (as base)
Methanol: CH3OH (solvent)

55
Q

How do you minimize losse?

A

(1) a solution of iodine in methanol and (2) sulfur dioxide

in pyridine.

56
Q

What is different about a karl fischer titration?

A

Iodine and SO2 in the KF reagent are
added by a burret to the sample in a
closed chamber protected from
atmospheric moisture.

57
Q

What is the lowest moisture content in a KF titration?

A

> 0.03%

58
Q

What is the endpoint of Karl Fischer?

A

The excess of I2 that cannot react
with the water produce a dark redbrown
color which aids in
determining the end point.

59
Q

What happens when the titration is a solid?

A

Karl Fischer reagent KFR is added directly as the titrant if the moisture in the sample s accesible

60
Q

What happens when the moisture of the solid sample is inaccessible to the reagent?

A

The moisture is extracted from the food with an appropriate solvent

61
Q

What is used for the titration?

A

Methanolic extract

62
Q

How to you stnadardize the reagent of the KFT?

A

Pretitration with KF reagent to determine KFR water eq

63
Q

What does the KFReq value represent?

A

Equivalent amount of water that reacts with 1mL of KFR

64
Q

What are major sources of error in the Karl Fischer titration?

A
  1. Incomplete moisture extraction
  2. ATmospheric moisture –> external air must not be allowed to infiltrate the reaction chaber
    Moisture adhering to walls of unit
  3. Interferences from certain food constituents
    - oxidation
    -acetal formation
    - reaction of unstaturated FA
65
Q

Coulometric KFT

A

Iodine is generated electrochemically during titration to titrate water in sample
Amount of iodine required to titrate the water is determined by the current needed to generate the iodine

66
Q

What moisture percent can you use the culometric Karl Fischer titration?

A

<0.03% ppm

67
Q

What are some physical methods to get rid of moisture?

A

Electrical

68
Q

What does Electrical method take advantage of?

A

Conductance - reciprocal of resistance 1/R

Capacitance - dielectric constant

69
Q

What do electrical methods need?

A

Calibration

70
Q

What is the dielectric constant of water?

A

80.37 at 20C

71
Q

What is the dielectric constant?

A

Measured as an index of capacitance

72
Q

Hydrometers?

A

LActometer
Brix Hydrometer
Alcoholmeters

73
Q

Lactometer?

A

Used to determine the density of milk

74
Q

Brix hydrometer

A

Saccharometer used for sugar solution such as fruit juices and syrups

75
Q

Alcoholmeters

A

Estimate alcohol content beverages

76
Q

Pycnometer

A

Measuring specific gravity by comparing the weights of equal volumes of a liquid and water in standardized glassware

77
Q

What is the specific gravity?

A

weight of sample/weight of water

78
Q

What are some other methods of moisture analysis?

A

Infrared analysis
Nuclear Megnetic Resonance NMR
Chromatography

79
Q

How can you measure the water activity ?

A

Vapour pressure of the headspace after the closed system containing food sample attains equilibrium

80
Q

What happens to the water in a container headspace?

A

Water will migitate out of the sample until the aw of the food and relative humidity are equal

81
Q

What is important with headspaces?

A

Temperature - 25C

82
Q

What are the dectors sued to determine the measurement of water activity in headspaces?

A

Dewpoint measurement, electric hygrometer sensors, direct measuremnt of pressure, freezing point determination

83
Q

What is loiture loss a function of?

A

Time and temperature

84
Q

What do carbohydrates release at higher temperatures?

A

Water

85
Q

When fatty acids are oxidized…

A

They increase the weight of the sample

5) FDSC 300 (14 decks)

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