Occurrence of Tetrahydro-β-carboline-3-carboxylic Acids in Commercial Foodstuffs

The occurrence of tetrahydro-β-carboline-3-carboxylic acids (THβC-3-COOHs) in foodstuffs was investigated. Spectral and chromatographic data showed the occurrence 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) in foodstuffs. The content of THβC-3-COOHs given as a sum of both THCA and MTCA was as follows: soy sauce, 94−517 mg/L; seasoning, 0.75−32.8 μg/g; table wine, 1.7−6.6 mg/L; beer, 0.3−17.9 mg/L; cider, 0.06−0.2 mg/L; liquor, 0−7.6 mg/L; wine vinegar, 3.9−9.7 mg/L; cider vinegar, 0.19−1 mg/L; yogurt, 0.05−0.15 μg/g; cheese, 0−3.4 μg/g; soft drinks, 0−0.45 mg/L; fruit juices, 0.1−5.1 mg/L; smoked fish, 0.08−0.4 μg/g; and bread, 0.16−3 μg/g. Usually MTCA was the major substance within THβC-3-COOHs, but bread and smoked fish contained more THCA. Experiments in which foodstuffs were spiked with formaldehyde and acetaldehyde proved the chemical formation of THCA and MTCA, respectively. It is concluded that the exogenous intake of these substances during the human ingestion of foods may be partially responsible of the reported endogenous presence of THβC-3-COOHs in the human biological tissues and fluids.