1. Felix Dyrek
Biological Investigation: Detection of Proteins
Introduction:
The experiment was performed in order to observe the methods which can be used to
demonstrate that proteins are present in different types of food.
Research Question:
In what kind of foods are proteins present and what kind of techniques are used to prove the
presence of proteins ?
Hypothesis:
If four samples of food,
* two of which are known to be rich in protein
* and two that lack in protein
come into contact with three different substances, being:
* concentrated nitric acid (xanthoproteic reaction),
* potassium hydroxide and copper (II) sulfate, together with potassium sodium tartrate, also
known as Biuret reagent , and
* ethanol, 89% alcohol by volume (process of denaturation),
then, the samples of ham and cheese will react to these substances, while lettuce and apple
samples will not.
Hypothesis Explanation:
Ham and cheese are rich in protein,lettuce and apple are not.A xanthoproteic reaction will be
produced when the samples which are rich in protein being combined with nitric acid.Its also
called ''the xanthoproteic test'' in which a yellow acid substance is formed by the action of hot
nitric acid on albuminous or proteid matter. It is changed to a deep orange-yellow color by the
addition of ammonia.
In combination with biuret reagent,the blue reagent will turn into violet in case proteins are
present.

2. Denaturation will appear when ethanol is added.Denatured proteins exhibit loss of solubility to
communal aggregation.No change will occur if this substances are being combined with the low
protein food apple or lettuce.
Compounds:
* apple
* swiss cheese
* iceberg lettuce
* plain ham
* concentrated nitric acid
* Biuret reagent
* ethanol (89%)
Variables:
* three reactant substances
* the reaction of the combined protein foods and the substances
Apparatus:
* lab apron
* gloves
* knife
* cutting board
*12 test tubes
* test tube rack
Method:
1.Put on the apron
2.Cut the cheese,apple,lettuce and ham small enough that it fits into the test tube

3. 3.Put the test tubes on a test table
4.Put the gloves on,take a test tube and fill a small amount of nitric acid into the tube
5.Observe what happens and write down your observations
6.Do the same with the other test tubes
7.Do the same again but this time use the biuret reagent and then the ethanol instead of nitric
acid
8.Write down your final observations
Data Collection & Processing:
Substance Sample of Food Observations
Concentrated Nitric Acid ham Sample turned yellow, transparency
increased
(xanthoproteic reaction) cheese Turned almost orange, acid turned a bit
cloudy
lettuce No visible reaction
apple No reaction, except apple turned a bit
brown due to oxidizing with air
Biuret reagent ham No visible reaction
cheese No visible reaction
lettuce No significant reaction – lettuce had a
tinge of blue
apple No visible reaction
Ethanol ham No visible reaction
cheese No visible reaction
lettuce No visible reaction
apple No visible reaction
Table 1: Reactions observed in the experiment.
Analysis & Conclusion:
In conclusion the results of this experiment dont fit 100% with the suggestions but at least the
xanthoproteic reaction prooved the presence of proteins and was therefore succesfull.running
another experiment with more efficient samples might hopefully let me observe the actually
expactable outcomes.

4. Bibliography
“Biuret reagent.” Wikipedia. February 18, 2008. March 2, 2008. <http://en.wikipedia.org/wiki/Biuret_reagent>
“Denaturation (biochemistry)” Wikipedia. February 9, 2008. March 2, 2008.
<http://en.wikipedia.org/wiki/Denaturation>
“Denature” The Free Dictionary by Farlex. 2003. March 2, 2008. <http://www.thefreedictionary.com/denature>
Dolson, Laura. “List of High-Protein Foods and Amount of Protein in Each.” About.com: Low-Carb Diets. January
21, 2008. March 2, 2008. <http://lowcarbdiets.about.com/od/whattoeat/a/highproteinfood.htm>
“Low Protein Diets.” Every Diet. March 2, 2008. <http://www.everydiet.org/low_protein_diets.htm>