1,2-Dicarbonyl compounds, formed from carbohydrates during thermal processing in the course of caramelization and Maillard reactions, are intensively discussed as precursors for advanced glycation endproducts in foods and in vivo. To obtain information about the uptake of individual compounds with commonly consumed foods, a comprehensive analysis of the content of 3-deoxyglucosone (3-DG), 3-deoxygalactosone (3-DGal), and methylglyoxal (MGO) together with 5-hydroxymethylfurfural (HMF) in 173 food items like bakery products, pasta, nonalcoholic and alcoholic beverages, sweet spreads, and condiments was performed. Following suitable cleanup procedures, 1,2-dicarbonyl compounds were quantitated after derivatization with o-phenylenediamine via RP-HPLC with UV detection. 3-DG proved to be the predominant 1,2-dicarbonyl compound with concentrations up to 410 mg/L in fruit juices, 2622 mg/L in balsamic vinegars, and 385 mg/kg in cookies, thus exceeding the corresponding concentrations of HMF. 3-DGal was found to be of relevance in many foods even in the absence of galactose. MGO was only of minor quantitative importance in all foods studied, except for manuka honey. Dietary intake was estimated to range between 20 and 160 mg/day for 3-DG and 5 and 20 mg/day for MGO, respectively.

1,2-Dicarbonyl compounds are formed in food during Maillard and caramelization reactions. 3-Deoxy-D-threo-hexos-2-ulose (3-deoxygalactosone, 3-DGal) and galactosone, two 1,2-dicarbonyl compounds originating from the degradation of galactose, were synthesized and converted to the respective quinoxalines, which were characterized by NMR spectroscopy. Analytical separation of the quinoxalines from the epimeric glucose-derived quinoxalines of 3-deoxyglucosone (3-DG) and glucosone was achieved by RP-HPLC on an RP-phenyl column. This method was used to study the relevance of galactose-derived 1,2-dicarbonyl compounds in a variety of foods. 3-DG and 3-DGal were quantified besides 3-deoxypentosone, methylglyoxal, and glyoxal after derivatization with o-phenylenediamine in lactose-hydrolyzed UHT milk, ranging from 2.5 to 18 mg/L and from 2.0 to 11 mg/L, respectively. The concentrations of both compounds tended to be higher in other lactose-hydrolyzed food items as well. During storage of lactose-hydrolyzed milk, the concentrations of the 3-deoxyhexosones first increased, but especially the concentration of 3-DGal tended to decrease on prolonged storage, pointing to lower stability of the compound. 3-DGal was also detected in galactose-free food items such as apple juice and beer. The possible formation of 3-DGal from 3-DG by 3,4-dideoxyglucosone-3-ene as an intermediate is discussed. Compared to the relatively high concentrations of 3-DG and 3-DGal, 3-deoxypentosone, methylglyoxal, and glyoxal were of only minor quantitative importance in all foods studied.

Methylglyoxal (MGO) is responsible for the pronounced antibacterial activity of manuka honey, in which it may reach concentrations up to 800 mg/kg. As MGO formed in vivo is discussed to play a role in diabetic complications, the metabolic transit of dietary MGO was studied within a 3 day dietary recall with four healthy volunteers. Determination of MGO in 24 h urine was performed with GC-MS after derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine, and D-lactate was quantified enzymatically. Following a diet virtually free from MGO and other glycation compounds, a defined amount of MGO (500 μmol in manuka honey) was administered in the morning of day 2. Renal excretion was between 0.1 and 0.4 μmol/day for MGO and between 50 and 220 μmol/day for D-lactate. No influence on excretion of both compounds was observed following administration of MGO. To investigate the stability of MGO under physiological conditions, a simulated in vitro gastrointestinal digestion was performed with MGO-containing honey. After 8 h of in vitro digestion, only 5-20% of the initial methylglyoxal was recovered. This indicates that dietary MGO is rapidly degraded during the digestion process in the intestine and, therefore, exerts no influence on the MGO level in vivo.

Following incubation of methylglyoxal and creatine under physiological conditions, N-(4-methyl-5-oxo-1-imidazolin-2-yl)sarcosine (MG-HCr) was isolated and identified by NMR and mass spectrometry. Due to its rapid formation, MG-HCr represents a specific product following "scavenging" of methylglyoxal by creatine. Using hydrophilic interaction chromatography coupled to mass spectrometry, MG-HCr was analyzed in urine samples of healthy volunteers. Daily MG-HCr excretion of nonvegetarians ranged from 0.35 to 3.84 μmol/24 h urine (median: 0.90 μmol/24 h urine) and of vegetarians from 0.11 to 0.31 μmol/24 h urine (median: 0.19 μmol/24 h urine), indicating that formation of MG-HCr in vivo is influenced by the dietary intake of creatine. The trapping of methylglyoxal by creatine may delay the formation of advanced glycation compounds in vivo and, therefore, could be of special importance in situations in which the body has to deal with pathophysiologically increased amounts of dicarbonyl compounds ("carbonyl stress"), for instance in diabetic patients.

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