Pentoses and Hexoses as Sources of New Melanoidin-like Maillard Polymers

Abstract

N-Substituted pyrroles (1), 2-furaldehyde (2), and N-substituted 2-formylpyrroles (3), formed in pentose (hexose) Maillard systems, were identified as components of extraordinary polycondensation activity. The polycondensation was studied in model experiments with 2), and N-(2-methoxycarbonylethyl)pyrrole (1b)/2-furaldehyde (2), respectively. MALDI-TOF-MS spectra indicated regular oligomers of up to 15-30 methine-bridged N-methyl(or N-2-methoxycarbonylethyl)pyrroles. With participation of aldehyde 2, furan rings instead of pyrrole rings were incorporated. The oligomers 5-11 were isolated and identified by MS and NMR techniques. A complementary experiment with N-methyl-2-[ 13 C]formylpyrrole ([ 13 CHO]-3a)/N-methylpyrrole (1a) was performed. The relevance of the new (type II) melanoidin-like oligomers/polymers in Maillard reactions is discussed and, in conclusion, a corresponding structure for native melanoidins is proposed. The oligomers 5, 6, 8, and 9 were tested for antioxidative activity in an iron(III) thiocyanate assay. Keywords: Model compounds for melanoidins; pyrroles from pentoses and hexoses; β-dicarbonyl pathway of the Maillard reaction; polycondensation of N-methylpyrrole with N-methyl-2-formylpyrrole (N-methyl-2-[ 13 C]formylpyrrole) or 2-formylfuran; polycondensation of N-(2-methoxycarbonylethyl)pyrrole with N-(2-methoxycarbonylethyl)-2-formylpyrrole or 2-formylfuran; MALDI-TOF-MS analysis of melanoidin-like oligomers/polymers; antioxidative activity of oligomeric model compounds

The role of lipids in nonenzymatic browning

“…Additional studies with 15 N-labeled amino acids showed that the melanoidins obtained exhibited signals in the pyrrole, indole, and amide region of the 15 N-NMR spectrum (Benzing-Purdie and Ratcliffe, 1986). These last results seem to be, at least partially, in agreement with the polypyrrolic structure proposed recently for these melanoidin-like Maillard polymers (Tressl et al, 1998a(Tressl et al, , 1998b, which is also very similar to the structure previously proposed for the melanoidins produced by oxidized lipid/protein reactions, see below (Hidalgo and Zamora, 1993a).…”

“…Brown pigments enzymatic pathway If the reaction mixtures of sugars and amines are submitted to exclusion chromatography, fractions can be obtained with molecular weights of about 7000 Da and even greater, and these fractions are predominant (> 95% p. w.) (Tressl et al, 1998b). However, so far it has not yet proved possible to isolate homogeneous high molecular weight Maillard products, and very little is known about the structure of these products, the so-called melanoidins.…”

“…Although, a priori, melanoidins obtained from sugars and oxidized lipids should be different, the recent studies of Tressl et al (1998aTressl et al ( , 1998b, Hidalgo and Zamora (1993a), and Hidalgo et al (1999), have demonstrated that it is possible to obtain the same, or very similar, polymers starting from both oxidized lipids and carbohydrates. To confirm this hypothesis in systems closer to real foods, new methods should be developed that allow either to fractionate melanoidins or to study the groups present in them.…”

Effects of surface Fe(III) oxides in a steel slag on the formation of humic-like dark-colored polymers by the polycondensation of humic precursors

“…In HS formation, biomacromolecules such as proteins, polysaccharides, lignins and polyphenols are hydrolyzed to low-molecular-weight compounds such as amino acids, sugar and quinone, which are referred to as humic precursors. These precursors are subsequently recombined via polycondensation reactions to form humic-like dark-colored polymers [1][2][3]. It has been reported that minerals in soil can influence the formation of dark-colored polymers that are formed by the polycondensation of humic precursors.…”

Genotoxic Maillard byproducts in current phytopharmaceutical preparations of Echinodorus grandiflorus

“…Maillard's-induced melanoidins pigments responsible for browning color in foods are polymeric compounds of pyrrol and furan rings formed during more advanced stages of the reaction (Tressl et al 1998). Remarkably, this is the first paper reporting in the appearance of such compounds in a phytomedicine.…”