Occurrence, Formation from d-Fructose and 3-Deoxyglucosone, and Activity of the Carbohydrate-Derived β-Carbolines in Foods

Abstract

β-Carbolines are naturally occurring bioactive alkaloids. In this work, carbohydrate-derived β-carbolines (βCs), 1-(1,3,4,5-tetrahydroxypent-1-yl)-β-carboline isomers ( 1a/b ), 1-(1,4,5-trihydroxypent-1-yl)-β-carboline ( 2 ), 1-(1,5-dihydroxypent-3-en-1-yl)-β-carboline ( 3 ), and 1-(1,2,3,4,5-pentahydroxypent-1-yl)-β-carboline ( 4 ) were identified and analyzed in commercial foods. The concentrations of βCs 1–4 in foods ranged from undetectable to 11.4 μg/g levels, suggesting their intake in the diet. Processed foods contained higher amounts than fresh or unprocessed foods, and the highest content was found in processed tomato and fruit products, sauces, and baked foods. βCs 1–3 were formed in foods during heating, and 1a/b were the main compounds. The formation of carbohydrate-derived βCs was studied in model reactions of tryptophan and carbohydrates. They formed in reactions of tryptophan with glucose under acidic conditions at temperatures higher than 80 °C. The formation of 1a/b was favored, but 2–3 increased at high temperatures. Noticeably, the βCs 1–3 formed in the reactions of tryptophan with fructose or sucrose, and the formation from fructose was much higher than from glucose. Thus, fructose was the main carbohydrate involved in the formation of 1–3 , whereas sucrose gave these βCs after acid hydrolysis. It is shown for the first time that the mechanism of formation of βCs 1–3 occurs from the sugar intermediate 3-deoxyglucosone that reacts with tryptophan affording these carbohydrate-derived βCs. A mechanism of reaction to give βCs 1–3 is proposed that relies on the tautomerism (keto–enediol or enamine–imine) of intermediates involved in the reaction. Carbohydrate βCs 1–4 were assessed as inhibitors of monoamine oxidase (MAO), as antioxidants, and for their interaction with DNA. They were not good inhibitors of MAO-A or -B, were poor antioxidants, and did not appreciably interact with DNA.

Formation, Characterization, and Occurrence of β-Carboline Alkaloids Derived from α-Dicarbonyl Compounds and l-Tryptophan

“…The βCs 1−3 arising from 3-deoxyglucosone were studied in a previous work. 15 In this work, the βC HET-βC was identified by HPLC-MS (m/z at 213 (M + H) + and 195 (213−18)) (Figure 8) and it appeared in many processed foods. Analysis was accomplished by HPLC with fluorescence detection (Figure S8), and the content ranged from undetected to hundreds of ng/g (Table 1).…”

“…20,22 These compounds have been previously identified in foods, and their complete spectral data have been reported. 15,20,22,23,35 Formation of βCs Derived from α-Dicarbonyl Compounds in Model Reactions and Foods. Model reactions containing Ltryptophan and glyoxal, methylglyoxal, 3-deoxyglucosone, or the carbohydrates, glucose or fructose, were carried out to evaluate the formation of α-dicarbonyl-derived βCs.…”

“…The carbohydrate-derived βCs 1−3 arising from 3-deoxyglucosone were also formed in those reactions as reported here and in a previous work. 15 The βCs derived from methylglyoxal (HET-βC) and glyoxal (HME-βC) were formed in lower amounts than the βCs 1−3 arising from 3-deoxyglucosone (Figure 7a,b). Fructose gave higher amounts of HET-βC and βCs 1−3 than glucose (Figure 7a,b).…”

“…Glyoxal afforded 1-hydroxymethyl-β-carboline (HME-βC), and methylglyoxal afforded 1-(1-hydroxyethyl)-β-carboline (HET-βC). In addition, L-tryptophan reacted with the α-dicarbonyl compound 3-deoxyglucosone, giving the so-called carbohydrate-derived βCs studied in foods: 15,20,22 The carbonyl group (C�O) in the α-dicarbonyl is converted into an alcohol (C-OH) substituent in these βCs. A mechanism for this is proposed in Figure 5.…”

“…In a recent work, we provided the first evidence that the so-called carbohydrate-derived aromatic βCs came from 3-deoxyglucosone, an intermediate formed from glucose and particularly fructose. 15 substances generated in foods and in vivo. Among them, the most important are glyoxal and methylglyoxal in addition to 3deoxyglucosone.…”