The reaction of l-dehydroascorbic acid (DHA) with primary
aliphatic amines including N
α-acetyllysine was examined by HPLC. A new aminoreductone,
2-deoxy-2-(propylamino)ascorbic acid
(1) was isolated and the structure elucidated by
spectroscopic data. Furthermore oxalic acid mono-
(2) and diamides (3) were identified as
important degradation products of DHA under Maillard
conditions. 3-Deoxy-3-(alkylamino)ascorbic acids
(4), typical condensation products of
l-ascorbic
acid and amines, were also detected in the reaction mixtures of DHA.
All products are formed
under oxidative and nonoxidative conditions from DHA.
Keywords: Maillard reaction; l-dehydroascorbic acid;
l-ascorbic acid; oxalic acid amides;
aminoreductones; protein glycation; protein cross link
Covalent binding of l-ascorbic acid (AA) to proteins
(protein ascorbylation) occurs during food
processing and storage and in vivo. It contributes, for example,
to browning and various changes
in the physical and physiological properties of proteins. Since
oxalic acid monoalkylamides (OMAs)
are formed in high yields from AA and primary amines under oxidative
conditions, it was determined
if OMAs also represent an ascorbylation product of proteins.
Therefore a polyclonal anti-OMA
antibody was raised, and a high-titer antiserum was obtained which is
specific against OMA. In a
competitive ELISA total binding inhibition was achieved by ascorbylated
protein, indicating that
ascorbylation of proteins leads to the formation of OMA. OMA is
only formed under aerobic
conditions. Proteins, which were glycosylated with other
carbohydrates such as glucose, did not
show cross-reactivity, indicating that the antiserum can be used to
detect OMA as a specific marker
for ascorbylation.
Keywords: l-Ascorbic acid; ascorbylation; immunochemical
detection; Maillard reaction; OMA
protein; oxalic acid monoalkylamide
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