Protein Analysis Flashcards
Methods of Protein Analysis
1) Kjeldahl
2) Dumas
3) Infrared Spectrop
Proteins are composed of (elements)
C-H-N (sometimes sulfur)
Proteins consist of
amino acids
Amino acid structure
Aromatic and Aliphatic
Protein Content (equation)
N content * conversion factor
Steps of Kjeldahl
1) Digestion (acid + catalyst)
2) Neutralization & Distillation
3) Titration
Why are metallic catalysts used
Mercury, copper, and selenium is added to sulfuric acid to complete digestion
What is potassium sulfate used for
increasing the boiling point in accelerate digestion
Advantages of Kjedahl
- Applicable to all types of foods
- Inexpensive (if not using an automated system)
- Accurate; an official method for crude protein
content - Has been modified (micro Kjeldahl method) to
measure microgram quantities of proteins
Disadvantages to Kjeldahl
- Measures total organic nitrogen, not just protein nitrogen
- Time consuming (at least 2 h to complete)
- Poorer precision than the biuret method
- Corrosive reagent
Dumas method
All carbon in the sample
is converted to carbon dioxide during the flash combustion.
The nitrogen oxides
are reduced to nitrogen in a copper reduction column at a high temperature (600◦C). The total nitrogen
(including inorganic fraction, i.e., including nitrate
and nitrite) released is carried by pure helium and
quantitated by gas chromatography using a thermal
conductivity detector
Advantages of Dumas
- Requires no hazardous chemicals.
- Can be accomplished in 3 min.
- Recent automated instruments can analyze up to 150 samples without attention.
Disadvantages of Dumas
- Expensive equipment is required.
- Measures total organic nitrogen, not just protein nitrogen.
Infrared Spectroscopy
Infrared spectroscopy measures the absorption of
radiation (near- or mid-infrared regions) by molecules in food or other substances
