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5) FDSC 300 > Lecture 3- Sample Preparation > Flashcards

Lecture 3- Sample Preparation Flashcards

(52 cards)

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1
Q

What is the flow od food analysis?

A

Sampling–> preprocessing–> processing–> testing

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2
Q

Why do we sample pre-treatement and sample processing?

A

Reducing sample size
Homogeous
Preventing changes in samples
Avoiding matrix interference during analysis

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3
Q

What is coning and quatering?

A

Gather the material into a cone –> flatten –> divide in half–> divide in quarters –> pick a quarter–> Repeat until you have a Sample

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4
Q

How do you reduce sample a sample?

A

Depend on physical size: blenders for solid and coning and quartering for powdered sample

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5
Q

Which smaples are usually heterogenous?

A

Samples obtained

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6
Q

What causes heterogeneneity?

A

Variations in the properties of differnet units within the sample

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7
Q

How can you homogenize?

A

Grinders, mixers, blenders

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8
Q

How do you choose the device to homogenize?

A

Depends on the composition of the sample

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9
Q

What do you use to homogenize a high fat high moisture food?

A

knife blades

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10
Q

What do you use to homogenize low fat low

A

grinder or mills

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11
Q

What are the reasons that we sould lose a sample?

A
  1. Losses as dust or particulates
  2. Losses through volatilization
  3. Losses due to adsorption
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12
Q

How do you stop the loss of a sample due to vessel?

A

Make sure the vesel is clean

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13
Q

Why would you lose a sample to dust/particles

A

Ashing –> dust get elsewhere
Ariflow –> due to changes in temp
Breathing –> dust goes places

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14
Q

How to reduce loss to dust

A

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

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15
Q

How to do you lose sample to volatilization?

A

During heating
Decreases in water during grinding solid during local heating
Elements may be volatile

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16
Q

Whatis blanching

A

Exposing a food to high heat via boiling water or steam fora short time

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17
Q

How do you migitate loss through volatilation

A

Use properly sealing vessel for wet ashing

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18
Q

Why would we have loss of sample due to adsorption?

A

Absorption of molecule to plastic or glass containers

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19
Q

Poly phenyloxidase

A

Add acid, stop oxidation (browning) or fruits

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20
Q

How do you migitate loss to absorption

A

Use pretreated glassware with a hydrated layer

Soak new glassware overnight with dilute nitric or hydrochoric acid

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21
Q

What are some changes that can occur in samples over time?

Study These Flashcards
A 
Enzymatic inactivation
Lipid oxidation
Microbila growth
Physical change
Contamination
22
Q

What happens during enzymatic degradation?

Study These Flashcards
A

Enzyme may degrade the food components being analyzed

23
Q

How do you migitate enzymatic degradation?

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A

Heat denaturation
Sotrage in freezer
pH
Adding reducing agents to prevent oxidative enzymes

24
Q

How do you wet ash?

Study These Flashcards
A

Acid and boiling

25
lipid oxidation
Unstaruated lipids are sensitive to oxidative degradation | Exposure t light can accelerate lipid peroxidation
26
How do you migitate lpid oxidation?
Storing under nitrogen or vacuum | Use anti-oxidant
27
What changes do microbial growth cause?
Microbial contamination Degrade food components Introduce foreign components
28
How do you mitigate microbial growth?
Addition of preservative Low Temperature storage Freeze drying Storage under modified atmosphere
29
What happens with physical change?
Drying Fluctuating storage temperature Fluctuatin gas pressure
30
How do you mitigate physical changes?
Storage in air tight humidity controlled containers | Maintain temperature
31
What are some sources of contamination?
``` Airborne Reagent Glassware Facilities Cross-contamination ```
32
Why is is important to reduce matrix interference?
Matrix components interfere with assay --> pigments interfering with colorimetric assay for reducing sugars
33
Examples of getting rid of the matrix
dry ashing, wet ashing,
34
How can sample preparation be performed?
1. Extractoin of target analytes | 2. Removal of itnerfering substances
35
What are the methods of extraction of analytes?
Digestion Solvent extraction Sorbent extraction Membrane Extraction
36
Contamination from ICP-MS
Wash equipment with acid to wash away contaminants
37
What is digestion?
Microwve, UV photolysis
38
What is solvent extraction?
Pressurized liquid extraction Supercritical fluid extraction -> lq, CO2 Microwave assisted extraction Solvent Assisted Flavour evaporation-> minor components Liquid phase microextraction
39
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 ```
40
What is membrane extraction?
Dialysis | Membrane extraction witha sorbent interface
41
What is a standard curve?
Independent -> X | Dependent -> Y
42
What is the point of making a standard curve?
To find the relationship between a independent and dependent variable through their slope
43
What is the lineary regression of a standard curve?
y=ax+b
44
What are confidence bands?
Define statistical uncertaincty of the regression line
45
What is the corrleation coefficient?
Defines how well the data fits toa straight line
46
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
47
What is the upper limit equation?
X+1.96*σ/√ n
48
What is σ?
The std. dev of the population
49
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 ```
50
What does outlier data tell you?
Says that the experiemtn is not well done | Due to errors in data ( human error, etc)
51
What are some other forms of error?
Sampling error Intentional misrepressentation of sample Instrument/assay condition failure Legitimate cases
52
Coefficient of Regression
Determine how accruate the line is

5) FDSC 300 (14 decks)

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