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Food Analysis > Analysis of Proteins > Flashcards

Analysis of Proteins Flashcards

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1
Q

Importance of analysis

A

Enzymes
Enzyme inhibitors
Functional proteins
Nutritional labeling

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2
Q

Kjeldahl

A

Digested with sulfuric acid + catalyst
Organic N –> ammonium sulfate
Neutralized with base
Distilled into boric acid
Create borate anions
Titrated with acid
Crude protein content

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3
Q

Kjeldahl Sample Prep

A

Solid foods are ground
Samples should be homogenous
No other prep

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4
Q

Kheldahl digestion

A

Nitrogen –> ammonium ions
C and H elements –> CO2 + water

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5
Q

Kjeldahl neutralization + distillation

A

Diluted with water
Sodium thiosulfate neutralizes
Ammonia distilled into acid

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6
Q

Kjeldahl calculation

A

Mol HCl = mol NH3 = mol N

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7
Q

Kjeldahl Advantage

A

All types of food
Simple
inexpensive
Accurate
Official method
Small quantities of sample

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8
Q

Kjeldahl disadvantages

A

Total organic N (not protein N)
Time-consuming
Poorer precision than biuret
Corrosive reagents
False + results
Bias from adulterants

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9
Q

Biuret Method

A

Violet purple color
Copper ions complex w/ peptide bonds
Read absorbance
BSA curve

Cereal, meat, soybean `

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10
Q

Biuret advantages

A

Less expensive than Kjeldahl
Rapid
Simple
Very few interferences
Does not detect non protein N

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11
Q

Biuret Disadvantages

A

Not very sensitive
Color varies w/ diff proteins
High concentration of ammonium salts interfere

Opalescence (high fat/carb)

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12
Q

Lowry method

A

Biuret + folin ciocalteau

Tyrosine and tryptophan residues
Read blue color
BSA curve

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13
Q

Lowry advantages

A

Sensitive
Less affected by turbidity

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14
Q

Disadvantages

A

Color varies w/ different proteins
Color is not proportional to [protein]
interference

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15
Q

BCA

A

Peptide bonds reduce Cu ions under high pH

Color change from green to purple
Phospholipids interfere

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16
Q

UV

A

Tryptophan and tyrosine residues show absorption

Need a pure system

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17
Q

Bradford method

A

Brilliant blue binds to protein
Color change (red to blue)
Change in absorbance proportional to concentration

Beer, potatoes

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18
Q

Bradford advantages

A

Rapid
Reproducible
Sensitive
No interference from cations, ammonium sulfate, polyphenols

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19
Q

Bradford disadvantages

A

Complex binds to cuvettes
Use glass or plastic cuvettes
Color varies w/ proteins

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20
Q

Anionic dye binding

A

Protein binds dye to form precipitate

Unbound dye is measured after removal of precipitate

Unbound dye inversely proportional to protein

Milk, wheat flour, soy product, meat

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21
Q

Anionic dye advantages

A

Rapid
Inexpensive
Relatively accurate
Lys in cereals

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22
Q

Anionic dye disadvantages

A

Not sensitive
Need calibration curve for a given food
Interferences and errors

23
Q

Rapid protein analyzer

A

Simple
Fast
No hazard chemicals
Approved
Unbound dye inversely proportional to protein

24
Q

Ninhydrin

A

Purple color formed
Hydrolysis of peptide bonds
Quantitate AA
Rapid

25
Q

Ninhydrin Disadvantages

A

Color varies w/ AA composition
Standard calibration curve needed

26
Q

Dumas method

A

Combust at high temp in the presence of O2

Traps to move certain compounds

27
Q

Dumas advantages

A

Alt to Kjeldahl
No hazardous chemicals
Quick
Can do many samples at once

28
Q

Dumas disadvantage

A

Expensive equipment
Nonprotein N included

29
Q

IR

A

Mid or near IR
Expensive
Rapid
Grain, cereal, meat, dairy

30
Q

Separate proteins by

A

Size
Charge
Absorption
Solubility
Heat stability

31
Q

Solubility characteristics determined by

A

Type and charge of AA

32
Q

Precipitate proteins by

A

Buffer
pH
Ionic strength
Dielectric constant
Temp

33
Q

Salting out

A

Proteins precipitate out as ionic strength is increased

34
Q

Isoelectric precipitation

A

Proteins aggregate at pI

35
Q

Solvent precipitation

A

Separate by solubility in different solvent mixtures

Acetone and ethanol decrease solubility (mostly)

36
Q

Separation by adsorption

A

Ion exchange chromatography
Affinity chromatography

37
Q

Ion exchange chromatography

A

Column has a certain charge
Proteins with that same charge exit first
Proteins with the opposite charge stick to the column and come out last

38
Q

Affinity chromatography

A

Column has a ligand for a certain protein
Unwanted proteins are washed through
Protein sticks to the ligand
Release with elusion

39
Q

Dialysis

A

Use semipermeable membranes
Low MW solutes diffuse out

40
Q

Ultrafiltration

A

Similar to dialysis
Semipermeable membranes with cutoffs

Molecules larger than the cutoff are retained
Molecules smaller than the cutoff pass through the membrane

41
Q

Size exclusion chromatography

A

Agarose or dextran = stationary phase
Molecules larger than the pores are excluded, leave 1st
Small molecules enter the pores and are retained

42
Q

Electrophoresis

A

Migration of charged molecules in a solution through an electric field
Polyacrylamide gels
Small proteins migrate faster

43
Q

Capillary Electrophoresis

A

Uses really thin capillary tubes
High efficiency separation
High electric field strengths
Minute amounts of sample
Precise quantitative analysis

44
Q

Amino Acid Analysis

A

Directly measure or estimate the essential AA content

Measure how well a protein is Digested, Absorbed, Utilized

45
Q

Protein Efficiency Ratio

A

Based on weight gain of rats
Test protein vs control diet
How much protein is used to build muscle, absorbed

46
Q

Net Protein Ratio

A

Value of a test protein for cell maintenance

47
Q

Biological Value

A

Absorbed N retained for maintenance or growth
Corrected for metabolic losses

48
Q

True digestibility

A

Based on amount of N ingested and feed intake
Corrected for losses in the feces

49
Q

PDCASS

A

AA score x true digestibility

50
Q

Solubility test

A

Find concentration where the protein is no longer soluble

51
Q

Emulsification

A

Tested by centrifugation or agitation
Wait for separation

52
Q

Foaming

A

Volume and stability are important
Overrun measures the air incorporated into the foam

53
Q

Gelation and gel formation

A

Measure rheological properties
Mixograph and farinograph

54
Q

Nitrogen titration

A

%N =
(Volume - Blank)(Normality)(MW) / Sample Mass

(All x 100%)

Food Analysis (19 decks)

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