Extracting not so Water-Soluble Pigments

Not all pigments from plants are water-soluble. Thus, they would have to be extracted using organic solvents.

CARROTS contain beta-carotene, which is the compound that gives it the orange colour.  This compound is very non-polar and would not dissolve in water (polar molecule), but instead it would dissolve in non-polar organic solvent, such as hexane.

Structure of beta-carotene molecule

Using hexane to extract yellow pigment from carrot

Yellow / orange pigment can also be extracted from TUMERIC.  This pigment arises from curcumin, which is a much more polar molecule as compared to beta-carotene.  However, it is more soluble in ethanol than in water, thus making ethanol a more suitable solvent to extract the pigment.

Structure of curcumin molecule

Footnote:

• Commonly used organic solvents:  ethanol, acetone, ethyl acetate, hexane...
• It is extremely important to check the health / environmental hazards of the organic solvents before using them!  This information can be found in the Material Safety Data Sheet (MSDS) that is available in many websites.
• Organic solvents must NOT be disposed into the sink!