Lecture 4/5- Moisture Analysis Flashcards
What are the compoenents of Proximate analysis?
- Moisture
- Ash
- Protein
- Fibre
- Fat
What does water allow?
Stucture
Indentity
Cheap filler
What is dry matter?
Often the expensive prt
Define nutritional part
Convinient for transport
Why is moisture determination important?
Food safety Shelf life Food quality Economic considerations Government regulation
What are the 4 forms of water in food?
Free
Capillary/trapped
Physically bound
Chemically bound
Characteristics of free water
Free from other constituents
Surrounded by other water constituents
Physiochemical same aspure water
Waht are the characteristics of capillary water?
WAter is held in narrow channels fromed by physical barriers by capillary forces
–> physiochemical like bulk water
What are the characteristics of physically bound water
Water is bound with other molecules (Proteins, Polysaccharides)
What are the characteristics of chemically bound water?
WAter is bound chemically (lactose monohydrate, salts)
Different physiochemical properties tob bulk water
What are the methods for moisture measurement?
- Drying methods
- Distillation methods
- Chemical methods
- Physical methods
What happens with drying methods?
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
What are some drying methods?
- Oven drying
- Freeze drying
- Infrared drying
What is Raoult’s Law?
The boiling point of water increases 0.512C for every 1 mol os solute dissolved in 1L of water
What is moisture loss a function of?
Time and temperature
At what temp does protein decomposition occur?
185C
What happens with carbs break down?
at higher temperature and release water
What could increase the weight of the sample during drying?
Oxidation of fatty acids
Convection oven
As heating takes place, water is lost a sample and moisture remains in teh chanber (105-110)
What are the disadvantages of drying methods
Longer analysis time
Loss of volatile components other than water
Larger temperature gradient
What is a forced air oven
Air is circulated by a fan
T can be higher and time can be shorter
What are the advantages to a forced air oven
Faster, efficient and water vapour will not condense to the fan
Microwave analyzer
Microwave drying is rapid technique
How do you make a microwave analyzer accurate?
microwave energy and time need to be defined
Vacuum Oven
The boiling point of substance is the temperature at whcih the vapor pressure of the liquid equals the pressure surroundin the liquid
What are the adavantages of the vacuum oven?
Drying under reduced pressure
Faster rate of evaporation
Removal of water with out decmposition
What is the vacuum overn based on?
The fact than water boils at lower T under vacuum
What is the purpose of the vacuum pump?
Reduce the ovens pressure to between 25-50mmHg
What are some common drying agents for vacuum ovens?
Anhydroud CaCl2
Anhydrous SO3
Phosphorous Pentaoxide P2O5
Concentrated H2SO4
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
What are factors that affect oven drying?
Temperature
Time
PArticle size
What is infra red drying
Penetrating infrared rays dry sample
Shorten drying time to 10-25mins
Heat of lamp is 1730-2230C
Is infrared drying approved by AOAC?
No
What is distillation
Recovery of water via distillation process, then the measurement of the volume of water
What is removed via distillation
H2O
When the vapour is cooled
What should a distillation solvent be like?
stable and used as a heat transfer media
What are the 2 version of distillation solvents?
- Immiscible/ non volatile ex mineral oil
2. Immiscible/volatile liquid ex toluene
What is the direct method of moisture determination
Water is removed quickly because of faster heat transfer –> may be less decomposition
Is the distillation method an AOAC approved technique?
YES
What is the other distiallation method?
Reflux distillation
What are the two solvents to distillation?
Mineral oil
Toluene
Mineral oil
immiscible in water
Volatile
Boiling point 200-310C
Density 0.8g/mL
Toluene
Immiscible with water Volatile Boiling point 110.6C Density 0.87g/mL flammable
Two other solvents?
Xylen and Tetrachlorethylene
Is it better to use volatile liquid or non volatile liquid?
Volatile, more effective
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
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
What is a Karl-Fisher Titration?
Adapted to food products that show erratic results when heated or submitted to a vacuum
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
What can you measure the Karl Fischer with?
ppm to %
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
what is the Karl Fischer based on?
Bunsen Reaction
2H2O+SO2+I2———->H2SO4+2HI
What does a bunsen reaction need?
Non-aq solvent (benzene- give erradic results, meth and pyridine(non aq base)
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).
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)
How do you minimize losse?
(1) a solution of iodine in methanol and (2) sulfur dioxide
in pyridine.
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.
What is the lowest moisture content in a KF titration?
> 0.03%
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.
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
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
What is used for the titration?
Methanolic extract
How to you stnadardize the reagent of the KFT?
Pretitration with KF reagent to determine KFR water eq
What does the KFReq value represent?
Equivalent amount of water that reacts with 1mL of KFR
What are major sources of error in the Karl Fischer titration?
- Incomplete moisture extraction
- ATmospheric moisture –> external air must not be allowed to infiltrate the reaction chaber
Moisture adhering to walls of unit - Interferences from certain food constituents
- oxidation
-acetal formation
- reaction of unstaturated FA
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
What moisture percent can you use the culometric Karl Fischer titration?
<0.03% ppm
What are some physical methods to get rid of moisture?
Electrical
What does Electrical method take advantage of?
Conductance - reciprocal of resistance 1/R
Capacitance - dielectric constant
What do electrical methods need?
Calibration
What is the dielectric constant of water?
80.37 at 20C
What is the dielectric constant?
Measured as an index of capacitance
Hydrometers?
LActometer
Brix Hydrometer
Alcoholmeters
Lactometer?
Used to determine the density of milk
Brix hydrometer
Saccharometer used for sugar solution such as fruit juices and syrups
Alcoholmeters
Estimate alcohol content beverages
Pycnometer
Measuring specific gravity by comparing the weights of equal volumes of a liquid and water in standardized glassware
What is the specific gravity?
weight of sample/weight of water
What are some other methods of moisture analysis?
Infrared analysis
Nuclear Megnetic Resonance NMR
Chromatography
How can you measure the water activity ?
Vapour pressure of the headspace after the closed system containing food sample attains equilibrium
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
What is important with headspaces?
Temperature - 25C
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
What is loiture loss a function of?
Time and temperature
What do carbohydrates release at higher temperatures?
Water
When fatty acids are oxidized…
They increase the weight of the sample
