Proteins or poly-L-lysine which were incubated in the presence of ascorbic acid, dehydroascorbic acid (ascorbylation), or various sugars (glycation) were analyzed by gas chromatography-mass spectrometry (GC-MS). To also detect more labile reaction products, the Maillard modified proteins or poly-L-lysine were enzymatically hydrolyzed and reacted with N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide to form the N(O)-tert-butyldimethylsilyl (tBDMS) derivatives prior to GC analysis. Under these conditions, the known Maillard products N (epsilon)-(carboxymethyl)lysine (1), oxalic acid mono-N (epsilon)-lysinylamide (2), and N (epsilon)-(carboxyethyl)lysine (3) could be simultaneously detected and quantified in glycated and ascorbylated proteins. Additionally, N (epsilon)-(1-carboxy-3-hydroxypropyl)-L-lysine (4) was identified for the first time as a Maillard product of proteins. Under the conditions applied here, 4 was found only in ascorbylated proteins or poly-L-lysine, but not in glycated proteins. Maillard-modified poly-L-lysine was further subjected to high-performance liquid chromatography (HPLC) analysis after enzymatic hydrolysis and formation of the phenyl isothiocyanate derivatized amino acids. Using this method, N (epsilon)-formyl-L-lysine (5), which cannot be distinguished from 2 by GC-MS analysis, was identified for the first time as a glycation product. Compound 5 is mainly formed from ribose, lactose, and fructose. The indicated Maillard products were quantified in beta-lactoglobulin (GC-MS) or poly-L-lysine (HPLC) which were glycated or ascorbylated using different precursors.

The reaction of L-tryptophan (Trp) with D-glucose under conditions that can occur during food processing and preparation was studied by high-performance liquid chromatography with diode array detection (HPLC/DAD). Besides the well-established glucose-tryptophan Amadori product (AP), (1R,3S)-1-(D-gluco-1,2,3,4,5-pentahydroxypentyl)-1,2,3, 4-tetrahydro-beta-carboline-3-carboxylic acid (PHP-THbetaC) was identified as an important product of this reaction. For preparation, PHP-THbetaC was obtained in high yields when Trp and D-glucose were reacted under strongly acidic conditions after heating in methanol. At elevated reaction temperatures (150 degrees C) 1-acetyl-beta-carboline (acetyl-betaC), was detected in significant concentrations. The mixtures were heated under variations of reaction time and temperature, and AP, PHP-THbetaC, and acetyl-betaC were quantified. In the presence of air oxygen or mild, food relevant oxidants, such as L-dehydroascorbic acid, PHP-THbetaC was readily oxidized to a product that was identified as the previously unknown 1-(D-gluco-1,2,3,4,5-pentahydroxypentyl)-beta-carboline (PHP-betaC). Formation of PHP-THbetaC and PHP-betaC in foodstuffs would deserve particular interest because multiple physiological activity of THbetaC and betaC derivatives has been shown previously.