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

Lecture 4/5- Moisture Analysis Flashcards

(85 cards)

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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
What are the adavantages of the vacuum oven?
Drying under reduced pressure Faster rate of evaporation Removal of water with out decmposition
26
What is the vacuum overn based on?
The fact than water boils at lower T under vacuum
27
What is the purpose of the vacuum pump?
Reduce the ovens pressure to between 25-50mmHg
28
What are some common drying agents for vacuum ovens?
Anhydroud CaCl2 Anhydrous SO3 Phosphorous Pentaoxide P2O5 Concentrated H2SO4
29
What are the advantages of vacuum drying?
- Reduced Temp 2- Reduction of loss volatiles 3- Less effect on degradation of some components 4- Shorten analysis time
30
What are factors that affect oven drying?
Temperature Time PArticle size
31
What is infra red drying
Penetrating infrared rays dry sample Shorten drying time to 10-25mins Heat of lamp is 1730-2230C
32
Is infrared drying approved by AOAC?
No
33
What is distillation
Recovery of water via distillation process, then the measurement of the volume of water
34
What is removed via distillation
H2O | When the vapour is cooled
35
What should a distillation solvent be like?
stable and used as a heat transfer media
36
What are the 2 version of distillation solvents?
1. Immiscible/ non volatile ex mineral oil | 2. Immiscible/volatile liquid ex toluene
37
What is the direct method of moisture determination
Water is removed quickly because of faster heat transfer --> may be less decomposition
38
Is the distillation method an AOAC approved technique?
YES
39
What is the other distiallation method?
Reflux distillation
40
What are the two solvents to distillation?
Mineral oil | Toluene
41
Mineral oil
immiscible in water Volatile Boiling point 200-310C Density 0.8g/mL
42
Toluene
``` Immiscible with water Volatile Boiling point 110.6C Density 0.87g/mL flammable ```
43
Two other solvents?
Xylen and Tetrachlorethylene
44
Is it better to use volatile liquid or non volatile liquid?
Volatile, more effective
45
Toluene distillation
Toluene and water will be collected in the receiving trap but will not mix Water is heavier so the lower layer is measured
46
What are the disadvantages of distillation?
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
What is a Karl-Fisher Titration?
Adapted to food products that show erratic results when heated or submitted to a vacuum
48
What is the advantages of the Karl Fisher Titration
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
What can you measure the Karl Fischer with?
ppm to %
50
What are the application of the Karls Fischer Method
Used in low and very low moisture foods (dehydrated veggies, spices, chocolate Also in non food applcations
51
what is the Karl Fischer based on?
Bunsen Reaction | 2H2O+SO2+I2---------->H2SO4+2HI
52
What does a bunsen reaction need?
Non-aq solvent (benzene- give erradic results, meth and pyridine(non aq base)
53
what is the best titrant ratio
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
what are the ingredients of KF reagents?
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
How do you minimize losse?
(1) a solution of iodine in methanol and (2) sulfur dioxide | in pyridine.
56
What is different about a karl fischer titration?
Iodine and SO2 in the KF reagent are added by a burret to the sample in a closed chamber protected from atmospheric moisture.
57
What is the lowest moisture content in a KF titration?
>0.03%
58
What is the endpoint of Karl Fischer?
The excess of I2 that cannot react with the water produce a dark redbrown color which aids in determining the end point.
59
What happens when the titration is a solid?
Karl Fischer reagent KFR is added directly as the titrant if the moisture in the sample s accesible
60
What happens when the moisture of the solid sample is inaccessible to the reagent?
The moisture is extracted from the food with an appropriate solvent
61
What is used for the titration?
Methanolic extract
62
How to you stnadardize the reagent of the KFT?
Pretitration with KF reagent to determine KFR water eq
63
What does the KFReq value represent?
Equivalent amount of water that reacts with 1mL of KFR
64
What are major sources of error in the Karl Fischer titration?
1. Incomplete moisture extraction 2. ATmospheric moisture --> external air must not be allowed to infiltrate the reaction chaber Moisture adhering to walls of unit 4. Interferences from certain food constituents - oxidation -acetal formation - reaction of unstaturated FA
65
Coulometric KFT
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
What moisture percent can you use the culometric Karl Fischer titration?
<0.03% ppm
67
What are some physical methods to get rid of moisture?
Electrical
68
What does Electrical method take advantage of?
Conductance - reciprocal of resistance 1/R | Capacitance - dielectric constant
69
What do electrical methods need?
Calibration
70
What is the dielectric constant of water?
80.37 at 20C
71
What is the dielectric constant?
Measured as an index of capacitance
72
Hydrometers?
LActometer Brix Hydrometer Alcoholmeters
73
Lactometer?
Used to determine the density of milk
74
Brix hydrometer
Saccharometer used for sugar solution such as fruit juices and syrups
75
Alcoholmeters
Estimate alcohol content beverages
76
Pycnometer
Measuring specific gravity by comparing the weights of equal volumes of a liquid and water in standardized glassware
77
What is the specific gravity?
weight of sample/weight of water
78
What are some other methods of moisture analysis?
Infrared analysis Nuclear Megnetic Resonance NMR Chromatography
79
How can you measure the water activity ?
Vapour pressure of the headspace after the closed system containing food sample attains equilibrium
80
What happens to the water in a container headspace?
Water will migitate out of the sample until the aw of the food and relative humidity are equal
81
What is important with headspaces?
Temperature - 25C
82
What are the dectors sued to determine the measurement of water activity in headspaces?
Dewpoint measurement, electric hygrometer sensors, direct measuremnt of pressure, freezing point determination
83
What is loiture loss a function of?
Time and temperature
84
What do carbohydrates release at higher temperatures?
Water
85
When fatty acids are oxidized...
They increase the weight of the sample

5) FDSC 300 (14 decks)

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