Lade Inhalt...

In what kind of foods are proteins present and what kind of techniques are used to prove the presence of proteins?

Referat / Aufsatz (Schule) 2008 4 Seiten

Biologie - Krankheiten, Gesundheit, Ernährung


Biological Investigation: Detection of Proteins


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 ?


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.

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.


- apple
- swiss cheese
- iceberg lettuce
- plain ham
- concentrated nitric acid
- Biuret reagent
- ethanol (89%)


- three reactant substances
- the reaction of the combined protein foods and the substances


- lab apron
- gloves
- knife
- cutting board
- 12 test tubes
- test tube rack


1.Put on the apron
2.Cut the cheese,apple,lettuce and ham small enough that it fits into the test tube
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:

illustration not visible in this excerpt

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.


386 KB
International Baccalaureate Biology SL Investigation Detection of Proteins Felix Dyrek




Titel: In what kind of foods are proteins present and what kind of techniques are used to prove the presence of proteins?