282 4 Carbohydrates
Various oxidation and condensation products
(R^1 =OH, CONHR; R^2 =OH, NHR) were
isolated from a heated, neutral solution. It can
be assumed from the structures shown that
protein cross-linkages are possible if, e. g., R 1
and R 2 represent theε-amino group of lysine
(Formula 4.83).
In conclusion, it should be mentioned here that
more recent studies also assume the direct elimin-
ation of water from the cyclic hemiacetals. This is
shown in Formula 4.85 for the direct formation of
maltol from theAmadoriproduct.
4.2.4.4.6 RedoxReactions........................................
In the course of the Maillard reaction, de-
oxyosones and reductones,e. g., acetylformoin
(cf. III, Formula 4.67), are formed. They can
react to give enol and triketo compounds via an
addition with disproportionation (Formula 4.86).
Redox reactions of this type can explain the
formation of products which are not possible ac-
cording to the reactions described till now. In fact,
it has recently been found that, for example, glu-
cose 6-phosphate and fructose-1,6-diphosphate,
which occur in baker’s yeast and muscle, form
4-hydroxy-2,5-dimethyl-3(2H)-furanone to a lar-
ge extent. Since the formation from hexoses (or
hexose phosphates) is not explainable, reduction
of the intermediate acetylformoin (Formula 4.87)
must have occurred. As shown, this reduction
can proceed through acetylformoin itself or
other reductones, e. g., ascorbic acid. Such re-
(4.87)dox reactions also play an important role in the
formation of the aroma substances 2-acetyl-1-
pyrroline and 2-acetyltetrahydropyridine, which
have been shown to exhibit slight oxidizability
ofα-eneaminols (cf. 5.3.1.6). Furthermore, such
processes also play a part in the formation of car-
boxymethyllysine (cf. 4.2.4.4.9).(4.86)4.2.4.4.7 StreckerReaction
The reactions betweenα-dicarbonyl compounds,
like the deoxyosones obtained in theMaillard
reaction, and amino acids are classed under the
term Streckerreaction. This reaction leads to
the formation of aldehydes (Streckeraldehydes),
CO 2 andα-aminoketones on oxidative decarb-
oxylation of theα-amino acids (Formula 4.88).
It occurs in foods at higher concentrations of
free amino acids and under more drastic reaction
conditions, e. g., at higher temperatures or under
pressure.
The aldehydes, which have one C-atom less than
the amino acids, possess a considerable aroma
potential, depending on the amino acid degraded.