Solubility Tests of Proteins- Definition, Principle, Procedure, Result, Uses

Solubility Tests of Proteins Definition

Solubility tests are tests performed to determine the ability of compounds to dissolve in a solvent, which is usually a liquid. These tests are essential to determine the size and polarity of unknown compounds and the presence of acidic and basic functional groups. Solubility tests for proteins and amino acids are qualitative tests that determine the presence and absence of different proteins. The determination of the solubility of proteins is an important factor that provides information on their functionality.

Objectives of Solubility Tests of Proteins

• To determine the solubility of proteins in different solvents.

Principle of Solubility Tests of Proteins

The solubility of proteins is the proportion of nitrogen present in the protein sample, which is in a soluble state under specific conditions. Amino acids present in proteins are generally soluble in water but are insoluble in non-polar organic solvents. The presence of amino and carboxyl groups in amino acids enables the amino acids and proteins to accept and donate protons to the aqueous solution. The solubility of a protein in a solvent is influenced by various factors like the molecular size, pH of the medium, hydration of the proteins, and the salting-in process. In the salting-in technique, the addition of salts generates an interaction between the surface ionic charges on the proteins and the electrolyte, preventing the aggregation of protein particles. Depending on all of these factors, the solubility of the protein in different solvents might differ.

Requirements

Reagent

• Sample solution
• Solvents (HCl, NaOH, Chloroform, Water)

Materials required

• Test tubes
• Test tube stand
• Dropper

Procedure of Solubility Tests of Proteins

1. A small amount of different solvents are taken in different test tubes.
2. To this, a few drops of the protein sample solution are added and mixed properly.
3. The test tubes are allowed to stand for about 5 minutes, and then the observations are made.

Result and Interpretation of Solubility Tests of Proteins

• Positive result: The positive result in the solubility test is demonstrated by the appearance of a clear solution with no precipitation of cloudiness.
• Negative result: The negative result in the solubility test is demonstrated by the appearance of a cloudy solution with precipitation.

Uses of Solubility Tests of Proteins

• The solubility tests of proteins help to understand the pattern of solubility of proteins which then helps in the detection and differentiation of such proteins.
• The solubility of proteins provides insight into the solubility of proteins during the development and testing of new protein composition.
• Solubility testing of proteins enables the selection of proteins for their use in liquid foods and beverages.
• The solubility of proteins also provides information about the amino acid composition and molecular weight.

Limitations

• The observation in solubility tests must be carried out carefully as chances of false-negative results might be prevalent.
• The test tubes should be allowed to stand for some time to provide some time for solubility.

References

• Zayas J.F. (1997) Solubility of Proteins. In: Functionality of Proteins in Food. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-59116-7_2
• D (2012). Biochemistry. Fourteenth Edition. Academic Publishers. Kolkata.
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