Lecture 3- Sample Preparation Flashcards
What is the flow od food analysis?
Sampling–> preprocessing–> processing–> testing
Why do we sample pre-treatement and sample processing?
Reducing sample size
Homogeous
Preventing changes in samples
Avoiding matrix interference during analysis
What is coning and quatering?
Gather the material into a cone –> flatten –> divide in half–> divide in quarters –> pick a quarter–> Repeat until you have a Sample
How do you reduce sample a sample?
Depend on physical size: blenders for solid and coning and quartering for powdered sample
Which smaples are usually heterogenous?
Samples obtained
What causes heterogeneneity?
Variations in the properties of differnet units within the sample
How can you homogenize?
Grinders, mixers, blenders
How do you choose the device to homogenize?
Depends on the composition of the sample
What do you use to homogenize a high fat high moisture food?
knife blades
What do you use to homogenize low fat low
grinder or mills
What are the reasons that we sould lose a sample?
- Losses as dust or particulates
- Losses through volatilization
- Losses due to adsorption
How do you stop the loss of a sample due to vessel?
Make sure the vesel is clean
Why would you lose a sample to dust/particles
Ashing –> dust get elsewhere
Ariflow –> due to changes in temp
Breathing –> dust goes places
How to reduce loss to dust
Never open the door of a hot furnace
Use plug of glass or quartz wool to collect particulates with combustion
Ash/ finely ground –> cover
Add reagaents slowly
How to do you lose sample to volatilization?
During heating
Decreases in water during grinding solid during local heating
Elements may be volatile
Whatis blanching
Exposing a food to high heat via boiling water or steam fora short time
How do you migitate loss through volatilation
Use properly sealing vessel for wet ashing
Why would we have loss of sample due to adsorption?
Absorption of molecule to plastic or glass containers
Poly phenyloxidase
Add acid, stop oxidation (browning) or fruits
How do you migitate loss to absorption
Use pretreated glassware with a hydrated layer
Soak new glassware overnight with dilute nitric or hydrochoric acid
What are some changes that can occur in samples over time?
Enzymatic inactivation Lipid oxidation Microbila growth Physical change Contamination
What happens during enzymatic degradation?
Enzyme may degrade the food components being analyzed
How do you migitate enzymatic degradation?
Heat denaturation
Sotrage in freezer
pH
Adding reducing agents to prevent oxidative enzymes
How do you wet ash?
Acid and boiling
lipid oxidation
Unstaruated lipids are sensitive to oxidative degradation
Exposure t light can accelerate lipid peroxidation
How do you migitate lpid oxidation?
Storing under nitrogen or vacuum
Use anti-oxidant
What changes do microbial growth cause?
Microbial contamination
Degrade food components
Introduce foreign components
How do you mitigate microbial growth?
Addition of preservative
Low Temperature storage
Freeze drying
Storage under modified atmosphere
What happens with physical change?
Drying
Fluctuating storage temperature
Fluctuatin gas pressure
How do you mitigate physical changes?
Storage in air tight humidity controlled containers
Maintain temperature
What are some sources of contamination?
Airborne Reagent Glassware Facilities Cross-contamination
Why is is important to reduce matrix interference?
Matrix components interfere with assay –> pigments interfering with colorimetric assay for reducing sugars
Examples of getting rid of the matrix
dry ashing, wet ashing,
How can sample preparation be performed?
- Extractoin of target analytes
2. Removal of itnerfering substances
What are the methods of extraction of analytes?
Digestion
Solvent extraction
Sorbent extraction
Membrane Extraction
Contamination from ICP-MS
Wash equipment with acid to wash away contaminants
What is digestion?
Microwve, UV photolysis
What is solvent extraction?
Pressurized liquid extraction
Supercritical fluid extraction -> lq, CO2
Microwave assisted extraction
Solvent Assisted Flavour evaporation-> minor components
Liquid phase microextraction
What is sorbent extraction?
Solid phase extraction Dispersive solid phase extraction Matrix solid phase dispersion Solid phase microextraction Solidphase dynamic extraction Stir Bar Sorptive Extraction Headspace Sorptive extraction Solid Phase aroma concentration extraction
What is membrane extraction?
Dialysis
Membrane extraction witha sorbent interface
What is a standard curve?
Independent -> X
Dependent -> Y
What is the point of making a standard curve?
To find the relationship between a independent and dependent variable through their slope
What is the lineary regression of a standard curve?
y=ax+b
What are confidence bands?
Define statistical uncertaincty of the regression line
What is the corrleation coefficient?
Defines how well the data fits toa straight line
What is outliner data?
Data point that is far outside the norm for a variable or population
- increase error variance
- reduce the power of a statistical test
- decrease normality
What is the upper limit equation?
X+1.96*σ/√ n
What is σ?
The std. dev of the population
How do you determine outlier Data?
Q test Qvalue= 𝑋2−𝑋1/𝑊 X1= outliner value X2= next closets value to X1 W total spread of all value obtained by substracting the lowest value from the highest value
What does outlier data tell you?
Says that the experiemtn is not well done
Due to errors in data ( human error, etc)
What are some other forms of error?
Sampling error
Intentional misrepressentation of sample
Instrument/assay condition failure
Legitimate cases
Coefficient of Regression
Determine how accruate the line is
