Formation of tetrahydro-β-carbolines and β-carbolines during the reaction of L-tryptophan with D-glucose

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-TH beta C) was identified as an important product of this reaction. For preparation, PHP-TH beta C 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-beta C), was detected in significant concentrations. The mixtures were heated under variations of reaction time and temperature, and AP, PHP-TH beta C, and acetyl-beta C were quantified. In the presence of air oxygen or mild, food relevant oxidants, such as L-dehydroascorbic acid, PHP-TH beta C 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-beta C). Formation of PHP-TH beta C and PHP-beta C in foodstuffs would deserve particular interest because multiple physiological activity of TH beta C and beta C derivatives has been shown previously.