Protein Analysis

Question 1

Methods of Protein Analysis

Answer 1

1) Kjeldahl
2) Dumas
3) Infrared Spectrop

Question 2

Proteins are composed of (elements)

Answer 2

C-H-N (sometimes sulfur)

Question 3

Proteins consist of

Answer 3

amino acids

Question 4

Amino acid structure

Answer 4

Aromatic and Aliphatic

Question 5

Protein Content (equation)

Answer 5

N content * conversion factor

Question 6

Steps of Kjeldahl

Answer 6

1) Digestion (acid + catalyst)

2) Neutralization & Distillation

3) Titration

Question 7

Why are metallic catalysts used

Answer 7

Mercury, copper, and selenium is added to sulfuric acid to complete digestion

Question 8

What is potassium sulfate used for

Answer 8

increasing the boiling point in accelerate digestion

Question 9

Advantages of Kjedahl

Answer 9

1. Applicable to all types of foods
2. Inexpensive (if not using an automated system)
3. Accurate; an official method for crude protein
   content
4. Has been modified (micro Kjeldahl method) to
   measure microgram quantities of proteins

Question 10

Disadvantages to Kjeldahl

Answer 10

1. Measures total organic nitrogen, not just protein nitrogen
2. Time consuming (at least 2 h to complete)
3. Poorer precision than the biuret method
4. Corrosive reagent

Question 11

Dumas method

Answer 11

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

Question 12

Advantages of Dumas

Answer 12

1. Requires no hazardous chemicals.
2. Can be accomplished in 3 min.
3. Recent automated instruments can analyze up to 150 samples without attention.

Question 13

Disadvantages of Dumas

Answer 13

1. Expensive equipment is required.
2. Measures total organic nitrogen, not just protein nitrogen.

Question 14

Infrared Spectroscopy

Answer 14

Infrared spectroscopy measures the absorption of
radiation (near- or mid-infrared regions) by molecules in food or other substances