Identification of Novel Colored Compounds Containing Pyrrole and Pyrrolinone Structures Formed by Maillard Reactions of Pentoses and Primary Amino Acids

Abstract

Heating of pentoses with alanine in a ratio of 10:1 in aqueous solution at pH 7.0 generated the yellow 2-[(2-furyl)methylidene]-4-hydroxy-5-methyl-2H-furan-3-one (1), being well in line with data reported in the literature. Decreasing the relative concentrations of the pentose produced further colored nitrogen-containing compounds, among which (S)-4-hydroxy-5-methyl-2-[N-(1‘-carboxyethyl)pyrrolyl-2-methylidene]-2H-furan-3-one (2) could be identified by spectroscopic and synthetic experiments. On the other hand, thermal treatment of an aqueous solution of pentose and l-alanine in the presence of furan-2-carboxaldehyde led to the formation of the novel red (2R)-4-oxo-3,5-bis[(2-furyl)methylidene] tetrahydropyrrolo[1,2-c]-5(S)-(2-furyl)oxazolidine and its 5(R)-(2-furyl)oxazolidine diasteromer (3a/3b), which were characterized by several 1D- and 2D-NMR techniques, LC/MS, and UV−vis spectroscopy as well as by synthesis of the chromophoric substructure. In addition, the red compounds (S)-4-[(E)-1-formyl-2-(2-furyl)ethenyl]-5-(2-furyl)-2-[(E)-(2-furyl)methylidene]-2,3-dihydo-α-amino-3-oxo-1H-pyrrole-1-acetic acid (4b) and the corresponding 2-[(Z)-(2-furyl)methylidene] isomer (4b) were identified in this Maillard mixture. Quantitative studies on the formation of these colorants clearly demonstrates the key role of 3-deoxypentos-2-ulose as an intermediate in the formation of 4a/4b. Reaction pathways leading to the colorants 2, 3a/3b, and 4a/4b from pentoses and alanine are discussed. Keywords: Maillard reaction; colored compounds; (S)-4-hydroxy-5-methyl-2-[N-(1‘-carboxyethyl)pyrrolyl-2-methylidene]-2H-furan-3-one; (2R)-4-oxo-3,5-bis[(2-furyl)methylidene]tetrahydropyrrolo[1,2-c]-5(S)-(2-furyl)oxazolidine; (S)-4-[(E)-1-formyl-2-(2-furyl)ethenyl]-5-(2-furyl)-2-[(E)-(2-furyl)methylidene]-2,3-dihydo-α-amino-3-oxo-1H-pyrrole-1-acetic acid

Recent Advances in the Chemistry of Strecker Degradation and Amadori Rearrangement: Implications to Aroma and Color Formation

“…According to Hofmann (1999), such intermediates, formed specifically from glycolaldehyde play an important role in the early melanoidization of Maillard mixtures compared with the longer chain analogs of ␣-hydroxycarbonyl intermediates. Apart from this free radical based browning pathway, Hofmann (1998b) also identified an ionic pathway that leads to the formation of low molecular weight non-melanoidin type colored compounds at the later stages of Maillard reaction. This pathway is mainly initiated by the further interactions of furan moieties such as furan aldehydes and acetylformoin (2,4-dihydroxy-2,5-dimethyl-3(H)-furanone), the latter compound is described as a chemical switch activated in the presence of excess of either primary or secondary amino acids to direct the formation of amino acid specific chromophores (Hofmann, 1998c).…”

“…In the case of glycolaldehyde/glyoxal couple, it is statistically less likely to generate a furan moiety through repeated aldol condensations, hence there is only one pathway of browning through ARP (free radical). With C 3 and C 4 precursors, aldol condensation can genarate furanoid species that lead to browning (Hofmann, 1998b). As to the variation in the differences of browning abilities (8 fold versus 256) among the precursors, this could be related to their relative ability to be reduced or to be oxidized in the reaction system.…”

A Novel Yellow Compound and Furpipate Derivatives Formed from Furfural or 5-Hydroxymethylfurfural in the Presence of Lysine

“…Our group has shown that furfural is a good indicator of the browning of orange juice, which is high in ascorbic acid, during storage (Shinoda et al, 2004;Shinoda et al, 2005). Although the chemical structure of the brown polymer is unclear, some low molecular weight yellow, red or blue pigments formed by the Maillard reaction of furfural or pentose have been reported (Hofmann, 1997(Hofmann, , 1998a(Hofmann, , 1998bAmes et al, 1993;Amoldi et al, 1997;Hayase et al, 1999;Sasaki et al, 2006). Recently our group also isolated and identified a novel yellow compound named furpipate (1; Fig.…”

Browning of Furfural and Amino Acids, and a Novel Yellow Compound, Furpipate, Formed from Lysine and Furfural

“…Our group has shown that furfural was a good indicator of the browning of orange juice, which is rich in ascorbic acid, during storage. 11,12) Some colored reaction products of furfural 13,14) or pentose [15][16][17] have been reported (Fig. 1).…”