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6266 J. Agric. Food Chem., Vol. 52, No. 20, 2004
Buttery and Takeoka
LITERATURE CITED
unknown seemed to be a lipid oxidation product because
concentration changes in the unknown also coincided with
concentration changes in other known lipid oxidation products.
A number of compounds were synthesized on the basis of
possibilities from interpretation of the mass spectrum, but none
matched that of the unknown. In 1993 Werkhoff et al. (10)
published the results of some studies on the identification of
meat volatiles. One of the unusual compounds they identified
was 5-ethylcyclopentene-1-carbaldehyde (Figure 1, structure 3),
the identity of which they had confirmed by synthesis. The mass
spectrum of this compound was consistent with that of the
tomato unknown. In addition, the GC retention data [personal
communication, G. E. Krammer, Haarmann and Reimer GmbH
(now Symrise GmbH), Germany] on both DB-1 (KI ) 1008)
and DB-Wax (KI ) 1422) were also consistent.
This compound is very likely formed by linolenic acid
oxidative degradation (possibly enzymatically induced) by a
variation of the well-known mechanisms already established for
the formation of the aliphatic noncyclic aldehydes (cf. ref 11).
With linolenic acid, formation of a free radical at carbon position
14 could lead to a pentadienyl radical between positions 12 and
16, which might ring close to give an ethyl cylopentenyl system.
The other requirement would be for the modified linolenic acid
molecule to break between positions 11 and 10, with position
11 being converted to an aldehyde group. Possibly this occurs
through â-scission via a position 11 hydroperoxy group. The
detailed mechanism of how this whole process occurs is,
however, not clear at present.
Conclusions. Of the three minor components discussed,
probably the most interesting is 5-ethyl-2(5H)-furanone because
its formation represents an additional pathway for the degrada-
tion of the key tomato aroma component, (Z)-3-hexenal.
The identification of pentyl nitrate is interesting because no
volatile alkyl nitrates had previously been reported in vegetables
and fruits, and the fact that it is a vasodilator may be important
in future studies on compounds in foods which could affect
human physiology.
The identification of 5-ethylcyclopentene-1-carbaldehyde
shows that this unusual lipid oxidation product can occur in
vegetables besides its first discovery in meat products.
Although the compounds discussed occur in minute amounts
in the tomato samples studied, there may be cases in breeding
new varieties, or in using different fertilizing and other growing
conditions, when these compounds could occur in much higher
amounts.
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Received for review April 12, 2004. Revised manuscript received July
9, 2004. Accepted July 10, 2004.
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