Analysis of tetrahydro-β-carboline-3-carboxylic acids in foods by solid-phase extraction and reversed-phase high-performance liquid chromatography combined with fluorescence detection

The presence and analysis of two tetrahydro-β-carboline-3-carboxylic acids in foods are studied. Sample preparation with benzenesulfonic acid strong cation-exchange columns followed by RP-HPLC–fluorescence allowed a reliable analysis and spectral characterization of 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (THCA) and 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (MTCA). Experimental data showed that upon oxidation tetrahydro-β-carboline-3-carboxylic acids gave rise to β-carbolines (norharman and harman) that were also chromatographically separated and their fluorescent profile monitored. This approach was useful to confirm identification of tetrahydro-β-carboline-3-carboxylic acids in foods. Several foods and beverages contained THCA and MTCA in varying proportions. Their occurrence in foods implies that diet is a source of these compounds in humans.