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Characterization of the chemical structure of novel colored Maillard reaction products from furan-2-carboxaldehyde and amino acids

Hofmann, T.
Journal of agricultural and food chemistry 1998 v.46 no.3 pp. 932-940
Maillard reaction, Maillard reaction products, food coloring, aldehydes, amino acids, alanine, proline, chemical structure, spectral analysis
Colored compounds formed by Maillard-type reactions from furan-2-carboxaldehyde and primary and secondary amino acids including L-alanine and L-proline, respectively, have been identified. When furan-2-carboxaldehyde was heated with L-proline in aqueous solution at pH 7.0, an intensely yellow compound was generated, which was identified as 5(S)-(2-carboxy-1-pyrrolidinyl)-2-hydroxy-(E,E)-2,4-pentadienal-(S)-(2-carboxypy rrolidine)imine (1) by application of several one- and two-dimensional NMR experiments and, in addition, by MS, UV, and IR spectroscopy. Further thermal treatment of compound 1 resulted, upon a ring closure reaction, in the formation of (E)-4,5-bis[(S)-2-carboxy-1-pyrrolidinyl]-2-cyclopenten-1-one (5), which has bee n, to our knowledge, as yet not reported in the literature. To confirm the proposed structures, L-proline was substituted by pyrrolidine and piperidine, leading to analogous N-cyanines (2 and 3) and cyclopentenones (4 and 6). On the other hand, thermal treatment of an aqueous solution of furan-2-carboxaldehyde and L-alanine led to the formation of the novel red compounds 8a and 8b, which were identified as (S)-4-[(E)-1-formyl-2-(2-furyl)ethenyl]-5-(2-furyl)-2-[(E)-(2-furyl)methylidene] -2,3-dihydo-alpha-amino-3-oxo-1H-pyrrole-6-acetic acid and the corresponding 2-(Z)-(2-furyl)methylidene isomer. This is the first time that chromophoric compounds comprising four linked rings with an amino acid moiety incorporated were identified in a Maillard reaction system.