Lecture 8- Protein Analysis Flashcards
What is protein analysis important?
Nutrition
Funtional properties
Economic consideration
What are the subunits of proteins?
Amino acids
What are the different structures of proteins?
Primary, secondary, tertiary, quaternary
What polypeptide bond links amino acids?
Peptide bond
What are the Non polar amino acids?
Glycine Alanine Valine Leucine Methionine Isoleucine
What are the polar amino acids?
Serine Threonine Cysteine Proline Asparagine Glutamine
What are the Aromatic amino acids?
Phenylalanine
Tyrosine
Tryptophan
What are the positively charged amino acids>
Lysine
Arginine
Histidine
What are teh negatively charged amino acids?
Aspartate
Glutamate
What is the distinguishing element in proteins?
Nitrogen
What is the range of nitrogen content in food proteins?
13-19%
What are the basic principles for protein determination?
- determination of N
- Peptide Bonds
- ARomatic Amino acids
- Dye binding capacity
- Ultraviolet absorptivity
What is the %Crude Protein?
Total N x Conversion Factor (~6.25)
What is total N?
Non Protein Nitrogen (NPN)
+
True Protein Nitrogen (TPN)
What are some examples of Non protein nitrogen?
Free amino acids Peptides Phospholipids Amino sugar nucleic acids Urea Nitrates Nitrites
In proximate analysis, what proteins content do we measure?
Crude , not True
What is the converstion factor?
Nitrogen to protein conversion assumes that 1kg of plant or animal protein contain a specific amount of nitrogen
6.25
If the nitrogen content ranges from ____% that means that nitrogen content is ___g/kg
13-19%
130-190g
What is the conversion factor for eggs? Wheat? Soy?
egg-6.25
wheat-5.33
soy-5.52
Calculation the converison factor for eggs
16% N therefore 1Kg egg proteins contains 160g N
1000/160=6.25
What are the two methods to determine crude protein?
Kjeldahl method--(N measured as ammonia NH3) Dumas Method (N measured as N2)
What is the Kjeldahl method based on?
Conversion of organic nitrogen (Total N) in food sample to ammonia (NH3)
What are the two steps in the Kjeldahl method?
Digestion: converts all N to NH3
Measurement of NH3: 1) distillation followed by titration 2) Colormetic methods 3) ammonium electrode technique
What happens in the digestion step?
Sample(N) +Conc H2SO4 (@300-400C)—–> CO2+ NH4+SO4+H2O
(release some toxic gas)
NH4+H2SO4–> H2SO4
( Clear solution, very stable salt in acid solution, nitrogen trapped in ammonium salts)
What is the first part of digestion?
PRotein nitrogen is liberated to form NH4 ions
H2SO4 oxidizes organic matter and combines with NH4 to form non volatile ammonium sulfate NH4SO4
Carbon and hydrogen elements are converted to CO2 and H2O
What does the catalyst do in Kjeldahl digestion?
Speeds up digestion/oxdiation
Seres and O carrier in oxidation
What are the catalysts used in Kjeldahl digestion? (3)
- Mercury oxide–> toxic, no longer used
- Selenium
- Copper
Why is K2SO4 added to Kjeldahl digestion?
The boiling point of H2SO4 is 290C, not enough to convert all protein N ot NH3 –> INCREASE BP