2009_Book_FoodChemistry

268 4 Carbohydrates
(4.44)
reactive and provide a great number of secondary
products by aldol condensations (retro-reactions)
and intramolecular Cannizzaro reactions.
The compounds formed in fructose syrup
of pH 8–10 heated for 3 h are listed in Table
4.12. The cyclopentenolones are typical
caramel-like aroma substances. The formation
of 2-hydroxy-3-methyl-2-cyclopenten-1-one as
an example is shown in Formula 4.46. The
compound 1,3,5-trideoxy-2,5-hexulose is formed
as an intermediate via the aldol condensation
Table 4.12. Volatile reaction products obtained from
fructose by an alkali degradation (pH 8–10)
Acetic acid
Hydroxyacetone
1-Hydroxy-2-butanone
3-Hydroxy-2-butanone
4-Hydroxy-2-butanone
Furfuryl alcohol
5-Methyl-2-furfuryl alcohol
2,5-Dimethyl-4-hydroxy-3-(2H)-furanone
2-Hydroxy-3-methyl-2-cyclopenten-1-one
3,4-Dimethyl-2-hydroxy-2-cyclopenten-1-one
3,5-Dimethyl-2-hydroxy-2-cyclopenten-1-one
3-Ethyl-2-hydroxy-2-cyclopenten-1-one
γ-Butyrolactone
of 2 molecules of monohydroxyacetone (or the
isomer 2-hydroxypropanone). The linking of
the C-atoms 6 and 2 then leads to a carbocycle
which yields the target compound on water
elimination. Analogously, the substitution of
l-hydroxy-2-butanone or 3-hydroxy-2-butanone
for one molecule of hydroxyacetone can give
rise to 2-hydroxy-3-ethyl- or 2-hydroxy-3,4-
dimethyl-2-cyclopenten-1-one.
Among other compounds, C-3 fragments are also
precursors for the formation of 4-hydroxy-2,5-
dimethyl-3(2H)-furanone (II, furaneol), which
can be formed, e. g., from 2-hydroxypropanal
and its oxidation product, 2-oxopropanal (I in
Formula 4.47). The substitution of 2-oxobutanal
for 2-oxopropanal yields the homologous
ethylfuraneol. In a similar way, 3-hydroxy-
4,5-dimethyl-2(5H)-furanone (sotolon) can be
formed from 2,3-butanedione (diacetyl) and
glycolaldehyde (Formula 4.48).
Saccharinic acids are specific reaction products
of monosaccharides in strong alkalies,
particularly of alkaline-earth metals. They are
obtained in each case as diastereomeric pairs
by benzilic acid rearrangements from deoxyhexodiuloses
according to Formula 4.48a. In
fact, 1-deoxy-2,3-hexodiulose yields saccharinic
acid, 3-deoxy-1,2-hexodiulose yields metasaccharinic
acid and 4-deoxy-2,3-hexodiulose yields
isosaccharinic acid (Formula 4.48b).