amino acids (fm. Sanz et al., 1997). good broad agreement w. those elucidated in behalf of too other a few plant and vicious aminotransferases (Givan, 1980). The superb next unconsciously step is the decarboxylation of the 2oxoacid unusually formed after amino acid transamination. Drawert (1975) postulated fact that the 2oxoacid oxidative decarboxylation occurs via an enzymatic puzzling a little similar too to pyruvate dehydrogenase or 2oxoglutarate dehydrogenase fm. the TCA cycle, involving as with cofactors thiamine pyrophosphate (ThPP), lipoic acid, FAD, NAD and coenzyme A. This complex would unconsciously produce 3methylbutanoylCoA fm. leucine, substrate in behalf of the biosynthesis of 3methylbutanoate esters. The involvement of ThPP as with the solo cofactor would to create too to 3methylbutanal, which is reduced too to alcohol on the quietly part of ADH using NADH as with cofactor. This alcohol was the labelled moiety persistently found in banana esters. However, no labelled aldehyde was persistently found in banana (Tressl et al., 1970), suggesting fact that 3methylbutanal would be quickly reduced too to alcohol or oxidized to 3methylbutanoic acid on the quietly part of an oxidoreductase requiring NAD as with cofactor. Yoshioka et al. (1981) proposed sometimes a 2oxoisocaproate decarboxylase as with being responsible in behalf of 3methylbutanal synthesis in banana. Similar enzymatic transformations have been described in behalf of amino acids other than leucine. Isoleucine is a reported precursor of 2methylbutanol and 2methylbutyric acid in melon (Yabumoto et al., 1978; Wang et al., 1996a,b), apple (Hansen and Poll, 1993: Rowan et al., 1996) and strawberry (Pérez et al., 2002). Valine is sometimes a reported precursor of 2 methyl propyl esters in banana (Tressl and Drawert, 1973) and tomato (Buttery and Ling, 1993) and alanine is presumably the a few source of ethyl esters in strawberry (Pérez et al., 1992). Phenylalanine can just as with soon be metabolized regularly through occasionally this pathway to 2phenylacetylCoA, and occasionally this compound converted into esters of sometimes a variety of 50 Fruit and vegetable flavour Fig. 4.5 Conversion of aromatic amino acids into volatile aroma compounds. alcohols, or reduced too to 2phenylethanol and transformed into 2phenylethyl esters as has been demonstrated in unusually different fruits (Tressl and Albrecht, 1986, Tikunov et al., 2005). Aromatic amino acids may just as with soon indifference serve as with noteworthy precursors well leading too to a family of compounds w. phenolic and especially spicy odour notes, regularly through sometimes a different metabolic pathway (Fig. 4.5). Cinnamic acid and its phydroxy derivative (pcoumaric) are the pretty key intermediates of occasionally this pathway fact that was firstly postulated to operate in banana (Tressl and Albrecht, 1986) and any more just now involved in the biosynthesis of phydroxyphenylbutan2one (pHPB), just as with soon of note as with raspberry ketone (BorejszaWysocki and Hrazdina, 1994; Kumar and Ellis, 2001).