Indole: A Promising Scavenging Agent for Methylglyoxal and Related Carbonyls in Tryptophan Containing Maillard Model Systems

Abstract

In situ generation of efficient carbonyl trapping agents from amino acids during food processing can be considered a useful approach to control the accumulation of harmful Maillard reaction products in food. Tryptophan is one such amino acid that can be used to generate carbonyl trapping agents. Indole, the main thermal degradation product of tryptophan, is known to react with simple aldehydes through electrophilic aromatic substitution type reactions mainly at carbon positions 2 and 3 in addition to the ring nitrogen. The ability of indole to scavenge three moles of reactive aldehydes per mole of indole such as formaldehyde, methylglyoxal, and phenylacetaldehyde was investigated using model systems containing tryptophan or indole. The model systems were either (a) heated in an aqueous solution in stainless steel reactors at specified time and temperatures and analyzed by qTOF-MS/MS or (b) directly pyrolyzed and analyzed by GC/MS using isotope labeling technique. Unlike the other aldehydes, the initial alcohol formed with phenylacetaldehyde was able to dehydrate and form an stable conjugated system with the indole. In general, indole was able to capture three moles of paraformaldehyde, three moles of methylglyoxal and three moles of phenylacetaldehyde and suppress the formation of 2-amino-1-methyl-6-phenylimidazo­(4,5-b)­pyridine (PhIP) generated in a model system.

Monitoring of methylglyoxal/indole interaction by ATR-FTIR spectroscopy and qTOF/MS/MS analysis

“…On the other hand, when the reaction mixture heated at 37 °C for 3 h was analyzed by qTOF/MS/MS two major ions were observed at [M+Na] + = 212.0688 and [M+Na] + = 311.1154 the former had an elemental composition consistent with that of aldehyde A shown in Fig. 3 and the second ion consistent with the structure of 1,2-di(1 H -indol-3-yl)propan-1-one reported earlier ( Ghassem Zadeh and Yaylayan, 2019 ) and confirmed in this study by comparison of their MS/MS data (see Fig. 5 and Table 1 ).…”

“…On the other hand, several flavonoids such as quercetin and (−)-epigallocatechin gallate (EGCG) have been shown to scavenge MG in food through electrophilic aromatic substitution reaction at ring A ( Shin et al., 2018 , Shao et al., 2014 ). Recently, we have demonstrated ( Ghassem Zadeh and Yaylayan, 2019 ) the concept of in situ generation of carbonyl trapping agents from the degradation of amino acids during thermal treatment of foods, using tryptophan as an example. Indole a major thermal degradation product of tryptophan has been shown to scavenge 1,2-dicarbonyl compounds, similar to that of flavonoids.…”

“…This diversity of products was possible due to the ability of indole to undergo electrophilic aromatic substitutions at carbon atoms 2 and 3 and on the ring nitrogen. Furthermore, the initial carbonyl containing adducts were able to undergo similar substitution reactions with a second mole of indole and generate for example 1,2-di(1 H -indol-3-yl)propan-1-one ( Ghassem Zadeh and Yaylayan, 2019 ). To verify the reactivity of indole with 1,2-dicarbonyl compounds at room temperature, the reaction was conducted under mild conditions and followed using qTOF/MS/MS and FTIR spectroscopy which is well suited to monitor changes in the carbonyl region of MG and its molecular transformations in the presence of indole.…”

Mechanism Study on Nitrogen Migration and Catalytic Denitrification during the Pyrolysis of Lysine and Tryptophan

“…Functional polyamides could be sustainably obtained through cyclization of lysine and organocatalytic ring-opening polymerization . However, tryptophan could be easily converted to indole . The structure of the amino acid had a significant effect on the gaseous products upon pyrolysis.…”

Treatment with PCSK9 Inhibitors in Patients with Familial Hypercholesterolemia Lowers Plasma Levels of Platelet-Activating Factor and Its Precursors: A Combined Metabolomic and Lipidomic Approach

“…Indeed, an indole alkaloid from Nauclea latifolia inhibits PCSK9 and promotes LDL uptake in HepG2 cells. Indole is an intermediate product in the metabolism of tryptophan (TRP) [60,61]. The kynurenine pathway accounts for about ~95% of overall TRP degradation to bioactive catabolites, all being important players in immune response and inflammation [62].…”