Agriculture Reference
In-Depth Information
It is an important aspect of adopting greener processes that the purifi cation of
products that arise from primary processing is kept to a minimum rather than
expending energy and resources to obtain materials of a purity that is not necessary
for the application in which they are being used. For example, low-energy
pyrolysis of a food grade carbohydrate source might generate a range of molecules
that have a sweet caramel fl avour; this can be used as a fl avour substance without
further purifi cation rather than attempting to isolate individual molecules.
Any process that leads to the production of a natural fl avouring ingredient
needs natural precursors and these can be isolated from crops, waste streams that
arise from crops or by fermentation. Other precursors can be obtained by
enzymatic hydrolysis of macromolecules or by controlled pyrolysis. The
interaction between these processes is shown in Fig. 12.6.
Although fermentation processes can produce a wide range of fl avour
molecules, yields are often low and therefore the fermenter volume and cost are
correspondingly high. An alternative approach is to use a solvent such as
supercritical carbon dioxide in which the fl avour molecules will be much more
soluble (Reverchon 1997) and to carry out biocatalysis in this medium.
12.3.1 Biocatalysis in non-aqueous solvents
Enzymes are generally more stable in supercritical carbon dioxide (scCO 2 ) than
they are in water and can catalyse a wide range of reactions that are useful in the
synthesis of fl avour molecules (Sheldon 2005). High conversion rates can be
achieved and recovery of both product and enzyme is straightforward. Examples
￿ ￿ ￿ ￿ ￿
Fig. 12.6
Primary processing options for the production of natural fl avour molecules.
 
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