Chemical and Functional Properties of Food Saccharides

HO
N
H 2
C
H 2
C
HC
CH
© 2004 by CRC Press LLC
NH CH COOH
O
R 2
OH
HC OH
CH 2 OH
18.4
CH COOH
+
R 1
Reaction 18.17
H 2 O
aldehydes was described by Rizzi. 65 The reaction called reductive amination consists
of the transamination of conjugated carbonyls in the presence of amino acids
to unsaturated amines with concomitant formation of Strecker aldehydes. Other
mechanisms yielding Strecker aldehydes propose decarbonylation followed by
deamination of amino acids, or decarboxylation of imine formed from a-amino
acid and a-keto acid. 18,66
18.9 MELANOIDINS
HO
HO
C
H 2
C
HC
CH
HC OH
HC
HC
HC
NH CH COOH
OH
CH 2 OH
CH
HC OH
CH 2 OH
R 1
N CH COOH
R 2
NH CH COOH
OH
R 2
CO2 H2O The term melanoidins is used for high-molecular-weight brown polymers that arise
at the final stage of the Maillard reaction. Although these polymers generally
represent the principal reaction products of Maillard reaction in foods and despite
extensive studies over the last two decades, the chemical nature of melanoidins is
not yet clear. One theory is that the formation of high-molecular-weight colored
products proceeds via polymerization of low-molecular-weight Maillard reaction
intermediates. For example, Tressl and coworkers reported on the formation and
characterization of a linear polymer (18.73) from N-methyl-2-
(hydroxymethyl)pyrrole as well as a branched polymer (18.74) from N-alkyl-2formylpyrrole,
N-alkyl-2-pyrrole, or 2-furaldehyde. 37,67 The corresponding pyrrole
C
H 2
C
HC
CH
OH
HC OH
CH 2 OH
R 1
NH CH COOH H2C NH CH COOH
N CH
R 2
R1 R1 N CH COOH HC N CH
CO2 H2O HO
HC
CH
CH
X X X
18.73 (X = O;
OH
HC OH
CH 2 OH
H 2 O
H 2 O
HO
C
HC
CH 2
NH
OH
HC OH
CH 2 OH
HC NH
HC
CH 2
CH
OH
HC OH
CH 2 OH
R 1
+
+
R 2 CHO
R 1 CHO