Isovaleric flavours

Methylbutanoates and methylbutyl esters are essential flavour compounds in fruit flavours they can be produced biotechnologically as mentioned before. Chowdary et al. [33] have described the production of a fruit-like flavour isoamyl isovalerate by direct esterification of isoamyl alcohol and isovaleric acid in hexane with the help of Mucor miehei lipase immobilised on a weak anion-exchange resin. 

The following example shows a strawberry flavour, analysed by the GC/MSD coupling technique using the TIC-method (Fig. 6.5). The identification of peak No. 5 (ethyl isovalerate), peak No. 14 (alpha-ionone) and peak No. 21 (ethyl 3-phenyl-glycidate) by the mass-spectrum shows the usefulness of this modem analysis technique. 

Volatile fatty acids p resent in wine may derive from the anabolism of lipids, resulting in compounds with even number of carbon atoms, by oxidative decarboxylation of a-keto acids or by the oxidation of aldehydes. Volatile fatty acids synthesised from a-keto acids are mainly propanoic add, 2-methyl-l-propanoic acid (isobutyric acid), 2-methyl-l-butanoic acid, 3-methyl-l-butanoic acid (isovaleric acid 3-methylbutyric add) and phenylacetic add. From lipid metabolism, the following fatty acids are reported butanoic add (butyric), hexanoic acid (caproic), odanoic acid (caprylic) and decanoic add (capric) (Dubois, 1994). Although fatty adds are charaderized by unpleasant notes (Table 1), only few compounds of this family attain its perception threshold. However, their flavour is essential to the aromatic equilibrium of wines (Etievant, 1991). 

The five-carbon short-chain isovaleric acid is apphed for the production of flavours and perfumes. Also, this acid is broadly used as intermediate for synthesis of insecticides, fungicides and depressants. The esters serve as plasticisers (Rdmpp 2005). 

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