Determination and occurrence of various tetrahydro-β-carboline-3-carboxylic acids and the corresponding N-nitroso compounds in foods and alcoholic beverages

An HPLC-fluorometric detection method and an HPLC-mass spectrometric (HPLC-MS) confirmation method were developed for the determination of 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (THβCCA), 1-methyl-THβCCA (MTHβCCA), and 1-(hydroxymethyl)-THβCCA (HMTHβCCA) in foods and alcoholic beverages. The occurrence of these THβCCAs in various foods and beverages is of considerable interest because of their role as neuro-modulators, and as precursors of N-nitroso-THβCCAs. Of various samples (nine soya sauce, 12 wines, 14 beers and ales, and 19 cured and smoked meats) analysed, the soya sauces and the wines contained more MTHβCCA (0.1-473 μg/g and 0.45̄ μg/g, respectively) than THβCCA (0–9μg/g and 0.01–0.05 μg/g, respectively). On the other hand, the cured smoked meats contained more THβCCA (0–7.6/gmg/g) than MTHμCCA (0–0.24μg/g). The beer samples contained low concentrations (0.04–0.82 μg/g) of both. Appreciable concentrations of HMTHβCCA were also detected in soya sauce (0.1–5.1 μg/g) but the smoked meats contained only traces (0–0.24). Five smoked meat samples also contained some (13–340 ng/g) N-nitroso-THβCCA, but no detectable amounts of N-nitroso-MTHβCCA. The other samples were not tested for these compounds. The study suggests for the first time that the presence of THβCCAs in nitrite-preserved foods (e.g. cured smoked meats) may lead to the formation of the corresponding, N-nitroso-THβCCAs.