1666 J. Agric. Food Chem., Vol. 47, No. 4, 1999
Cutzach et al.
sible for slightly “honeyed” or “rancid” aromatic zones
(Cutzach et al., 1998). These compounds were known
as possible derivatives of Maillard reactions. In fact,
reactions between glucose and phenylalanine when they
are heated together produce large quantities of 2,5-
furandicarbaldehyde and furylhydroxymethyl ketone
(Baltes et al., 1988). Furthermore, 2,5-furandicarbal-
dehyde and furylhydroxymethyl ketone are also major
components in the aroma of honey (Graddon et al.,
1979). These two compounds were formally identified
by their mass spectrum, retention index (1985 and 2009,
respectively, on a BP-20 polar column), and GC-FTIR
(Figures 2 and 3). Identification was confirmed by co-
injection with standard reference compounds obtained
by organic synthesis.
These molecules were both present in toasted wood:
2,5-furanedicarbaldehyde was more abundant, while
furylhydroxymethyl ketone was usually present only in
trace amounts. Both of these molecules may also be
identified in the pyrolysis of glucose. According to Baltes
and Mevissen (1988), the Maillard reactions produced
by heating the glucose-proline mixture, or in particular
glucose-phenylalanine, give much higher concentra-
tions. No 2,5-furandicarbaldehyde was found when
fructose was pyrolyzed alone.
Hydroxymaltol, 2,5-furanedicarbaldehyde, and furyl-
hydroxymethyl ketone have also recently been identified
in extracts of old sweet fortified wines (vins doux
naturels), such as Banyuls, Rivesaltes, and Port (Cutzach
et al., 1998). Hydroxymaltol and furylhydroxymethyl
ketone, when pure, had a “honey” and “toasty-caramel”
odor detected after combined gas chromatography and
olfactory detection. Nevertheless, 2,5-furanedicarbalde-
hyde had a “honey” odor detected after combined gas
chromatography and olfactory detection, whereas the
pure compound had a “cheese” odor.
Con fir m a tion of th e Id en tifica tion of a Molecu le
w ith a “Toa sty” Ch a r a cter P r od u ced by P yr olysis
of Glu cose a n d by Hea tin g th e P r olin e-Glu cose
Mixtu r e. The chromatographic peak corresponding to
odorous zone ZO 7 in the heated glucose-proline
mixture (Cutzach et al., 1997) had not previously been
formally identified. Its fragmentation by electron impact
had led to the supposition that it had a molecular weight
of 144. With the help of bibliographical research (Ledl
et al., 1984; Schieberle, 1992; Kim and Baltes, 1996;
D’Arcy et al., 1997), its electron impact mass spectrum
and retention index have led to the formal identification
of this compound as 2,4-dihydroxy-2,5-dimethyl-3(2H)-
furanone, or acetylformo¨ıne (Figure 4). This compound
was also present in extracts of old sweet fortified wines
(vins doux naturels) (Cutzach et al., 1998), as well as
pyrolyses of glucose and fructose, but was mainly formed
when a sugar was heated with an amino acid. Acetyl-
formo¨ıne has not always been identified in toasted wood
extracts. It seems, therefore, that the conditions under
which oak wood is toasted are not conducive to the
formation of this molecule. This compound was probably
broken down by dehydration and reduction into furaneol
(4-hydroxy-2,5-dimethyl-3(2H)-furanone) (Ledl et al.,
1984; Schieberle, 1992; Kim et al., 1996). Furthermore,
acetylformo¨ıne, and certain other aliphatic isomers, may
be formed by the breakdown of 2,3-dihydro-3,5-dihy-
droxy-6-methyl-4H-pyran-4-one (DDMP) on heating and
can coexist in a keto-enolic balance (Kim and Baltes,
1996). This product, when pure, has a “toasty-caramel”
odor detected after combined gas chromatography and
olfactory detection.
CONCLUSION
We confirm the presence of acetylformo¨ıne in heated
extracts of various sugars and sugar mixtures with
amino acids. This molecule was not detected in extracts
of toasted oak wood.
Both 2,5-furandicarbaldehyde and furylhydroxym-
ethyl ketone were identified in toasted oak for the first
time. These molecules may be formed by direct pyrolysis
of glucose. The pyrolysis of fructose does not result in
the formation of 2,5-furanedicarbaldehyde. These two
molecules were also present when sugars and amino
acids were heated together, and in particular in the
glucose-phenylalanine mixture.
Hydroxymaltol is only identifiable in trace amounts
in toasted wood.
The presence of these compounds in oak from barrels
toasted according to cooperage techniques may be
attributable to Maillard reactions and pyrolysis of
sugars.
Future research will focus on developing a sufficiently
sensitive method for measuring concentrations of these
compounds and determining their perception thresholds
in wine. These data will make it possible to draw
conclusions concerning the organoleptic impact of these
substances and the influence of toasting intensity.
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