Formation of Tetrahydro-β-carbolines and β-Carbolines during the Reaction of l-Tryptophan with d-Glucose

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Abstract
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-β-carboline-3-carboxylic acid (PHP-THβC) was identified as an important product of this reaction. For preparation, PHP-THβC 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 °C) 1-acetyl-β-carboline (acetyl-βC), was detected in significant concentrations. The mixtures were heated under variations of reaction time and temperature, and AP, PHP-THβC, and acetyl-βC were quantified. In the presence of air oxygen or mild, food relevant oxidants, such as l-dehydroascorbic acid, PHP-THβC was readily oxidized to a product that was identified as the previously unknown 1-(d-gluco-1,2,3,4,5-pentahydroxypentyl)-β-carboline (PHP-βC). Formation of PHP-THβC and PHP-βC in foodstuffs would deserve particular interest because multiple physiological activity of THβC and βC derivatives has been shown previously. Keywords: Maillard reaction; tryptophan; tetrahydro-β-carboline; β-carboline