2009_Book_FoodChemistry

272 4 Carbohydrates
(4.52)
The reasons for the partial stability of such
Amadori compounds in comparison with imines
can be explained by the cyclic molecular
structures.
The imine (Formula 4.52) formed by the reaction
of glucose with the amine is easily converted to
the cyclic hemiaminal, α- andβ-glucosylamine.
However, N-glycosides of this type are relatively
instable because they very easily mutarotate, i. e.,
they are easily hydrolyzed via the open-chain
imine or are converted to the respective α- and
β-anomer. However, the Amadori rearrangement
leads to furanose, which as a hemiacetal, has
a stability to mutarotation comparable with that
of carbohydrates.
The Amadori compounds can react further with
a second sugar molecule, resulting in glycosylamine
formation and subsequent conversion
to di-D-ketosylamino acids (“diketose amino
acids”) by an Amadori rearrangement:
(4.54)
4.2.4.4.2 Formation of Deoxyosones
Amadori products are only intermediates formed
in the course of the Maillard reaction. In spite of
their limited stability, these products can be used
under certain conditions as an analytical indicator
of the extent of the heat treatment of food. Unlike
the acidic (pH <3) and alkaline (pH >8) sugar
degradation reactions, the Amadori compounds
are degraded to 1-, 3-, and 4-deoxydicarbonyl
compounds (deoxyosones) in the pH range 4–7.
As reactive α-dicarbonyl compounds, they yield
many secondary products. Formulas 4.54–4.57
summarize the degradation reactions starting with
the Amadori compound.
Analogous to fructose (cf. Formula 4.37), aminol-deoxyketose
can be converted to 2,3-eneaminol
as well as 1,2-eneaminol (Formula 4.54) by
enolization. Analogous to the corresponding
1,2-enediol, water elimination and hydrolysis of
the imine cation gives 3-deoxy-1,2-diulose, also
called 3-deoxyosone (Formula 4.55).
Like the corresponding 2,3-enediol, the 2,3-
eneaminol has two different β-elimination
options. Formula 4.56 shows the elimination of
the amino acid by a retro-Michael reaction with