Natural aroma chemicals for use in foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 217

Many aldol-type reactions take place spontaneously, or with gentle heating;
for example, 5-methyl-2-phenyl-2-hexenal [10.26] is readily formed from
isovaleraldehyde [10.27] (obtained from eucalyptus oil) and phenylacetaldehyde
[10.28] (from the fermentation of phenylalanine - see below).

[10.26] [10.27] [10.28]

10.6 Natural aroma chemicals by biotechnology
10.6.1 Fermentation products
Language is a tricky beast, and never more so than here. 'Biotechnology'
invokes scientists in white coats in laboratories and scientists are, as we
are informed by the press, and know from the movies, at best, naive and bit
barmy ('the nutty professor'), and even more often deranged sociopaths
(Dr Strangelove, Dr Frankenstein). The term 'fermentation' is more acceptable
and 'brewing' is positively cuddly. So this is the cuddly fl uffy section on brewing
derivatives, or more generally by the use of different varieties of yeast
( Saccharomyces spp.)
The single biggest use of yeast (in chemical terms) is in the production of
ethanol, both for consumption in alcoholic liquors and for use in fuel. Ethanol
[10.29] is also of great importance in fl avours, where it can contribute to the
fl avour, act as a solvent or be considered an additive (as E1510). However, while
it is the primary product of fermentation, other highly valuable materials are
produced as well. The isolation of dimethyl sulfi de [10.1] from the effl uent gases
has already been mentioned; the residues after the ethanol has been distilled off,
the fusel oils (from the German 'fusel', referring to 'bad spirits') are the main
source of 'isoamyl alcohol', a mixture of 2-methyl- and 3-methyl-butan-1-ol
[10.30], together with smaller amounts of other alcohols such as butan-1-ol and
hexan-1-ol. The residues after the removal of the isoamyl alcohols can be further
processed to give natural pyrazines. These are the simple alkyl pyrazines,
predominantly the isomers of dimethylpyrazine, e.g. 2,3-dimethylpyrazine [10.31],
trimethylpyrazine and ethyldimethylpyrazines (such as [10.32]); there is little
tetramethylpyrazine and the cyclic pyrazines such as 5,6,7,8-tetrahydroquinoxaline
are not present. Finally, from the residues of the residues of the residues, the
carotenoid derivative β -damascenone [10.33] can be isolated.
Table 10.2 shows the structures of these materials and their boiling points. The
commercial feasibility of isolating these materials derives solely from their origins

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