Sources of flavours and fragrances prone to thermal degradation

Byshaheen shaikh

Many molecules are prone to thermal degradation i.e. change in molecular composition under the action of heat / high temperature. When heat is applied, bonds between atoms which form the molecules often break down.  Aromatic molecules which form the sources of flavours and fragrances are no exception.

On account of this fact of a fundamental nature, the extraction of flavours and fragrances requires a process that does not employ high temperatures. The supercritical fluid extraction process using carbon dioxide as the supercritical fluid i.e. the CO2 SCFE process fits this requirement completely.

Here is a list of the properties of CO2 that make it an ideal fluid for this extraction process. Carbon dioxide has a:

  • Critical temperature of 31.10C, which is around the ambient temperature improving its compatibility with temperature-sensitive compounds.
  • More manageable critical pressure of 73.9 bar.
  • Non-flammable and non-toxic nature.
  • Customizable density to upgrade its solvent power.
  • Ample availability in pure form.
  • Comparatively low cost.

Because the critical temperature of CO2 is approximately equal to the room temperature, it does not require the SCFE process to utilize higher temperatures. At the very least, thermal distortion is minimized. At best, it is eliminated – making the process an excellent tool for the extraction of flavours and fragrances.

A supercritical fluid is one with its pressure and temperature respectively above its critical pressure and critical temperature. Such fluids have properties that can be similar to that of its:

  • Liquid state
  • Gaseous state
  • Somewhere in between

The solvent power of such a fluid i.e. its capacity to dissolve the required molecule (called target molecule) from the raw material rises and falls with increase and decrease in density. And, its density changes by a large amount when its pressure and temperature change by a relatively small magnitude:

  • At high pressure, the solvent power of supercritical fluids is high.
  • At low pressure, its solvent power is low.

The supercritical fluid extraction process dissolves the target molecule from the raw material at high pressure. This operation takes place in the extractor. At low pressure, the target molecule separates out from the fluid. Since the extraction action is based on pressure difference, there is very little or zero contamination of the target molecule by the fluid.

And if CO2 is used for the SCFE procedure, the process temperature is around the room temperature, further minimizing the possibility of thermal distortion. The process is preferred in the extraction of flavours and fragrances because the molecules of flavour and fragrance raw materials are prone to thermal degradation.

Steam distillation and hydrodistillation were used earlier for extraction of fragrances and flavours but fell out of favour because they used high temperatures. The solvent extraction method similarly receded because it leaves solvent residues in the extracted flavours and fragrances.

More than 250 types of plants serve as the source for the 500-plus raw materials used in the flavour and fragrance industry. The most popular oils in the industry include rose oil, tuberose absolute, angelica root oil, jasmine absolute, ambrette seed oil, and orange flavor oil.