Mutation Research/Genetic Toxicology and Environmental Mutagenesis
Trigonelline, a naturally occurring constituent of green coffee beans behind the mutagenic activity of roasted coffee?
Introduction
Coffee is one of the most popular beverages in the world, especially in the Scandinavian countries; in Finland the consumption is an average 5.3 cups per day [1]. Concerns about the safety or health risk associated with drinking coffee have resulted in a number of scientific publications. Recently, the International Agency on Cancer concluded that for urinary bladder cancer there was some evidence that coffee drinking may constitute a certain carcinogenic risk for humans [2]. There was no evidence that coffee could cause cancer to other organs. Furthermore, there is some epidemiological evidence that heavy coffee consumption may reduce the risk of colon cancer [3]. The roasting of coffee produces a wide range of new compounds; some of which are known to be mutagenic while others possess antimutagenic effects [4]. Many investigators have reported measurable mutagenic activity in Salmonella strain TA 100 without metabolic activation due to the presence of methylglyoxal 5, 6, 7, 8, 9, 10, 11. Also, the H2O2 content was shown to contribute to the mutagenic activity in coffee [12]. Mutagenic activity in Salmonella strain TA 98 with metabolic activation has been reported for coffee in some studies 13, 14, 15, 16. The mutagenic heterocyclic amine 2-amino-3,4-methylimidazo-[4,5-f]quinoline (MeIQ) has been identified in an extract of high-temperature roasted coffee [15], but in another report, MeIQ was not detected in roasted coffee [17]. The results are thus somewhat contradictory, and the presence of other heterocyclic-amine-like mutagens in roasted coffee has also been observed 14, 16. Heat treatment of coffee causes great chemical changes to the coffee beans. Among the naturally occurring heat-sensitive components in the dry bean, are trigonelline, present at an average concentration of about 1% (calculated on a dry basis), amino acids (0.8%) and glucose (0.04%) 18, 19. Trigonelline is transformed into several volatile products when heated, e.g. pyridines and pyrroles [20]. Green coffee beans have no mutagenic activity, but after 2 min roasting, when the temperature of the beans had reached 120°C, mutagenic activity was already observed [21]. It has earlier been shown that mutagenic activity can be produced when heating model reactions of amino acids together with creatine in the presence or absence of glucose [22]. Recently, Knize et al. [23]reported the formation of mutagenic activity when single amino acids or binary combinations of amino acids were heated without creatine. In this study we have investigated whether mutagenic activity could be produced by trigonelline when heated alone or together with amino acids or glucose in a model system mimicking coffee roasting. The mutagenic response was quantified using Salmonella tester strains, and the mutagenic compounds were characterised by chromatography and a comparison with the mutagenic heterocyclic amines found in cooked meats.
Section snippets
Chemicals
All commercially available chemicals were of analytical grade. Solvents were of HPLC grade. Acetonitrile, methanol and dichloromethane were purchased from Merck (Darmstadt, Germany). Water was taken from a Milli-Q water purification system (Millipore, Bedford, MA, USA). Arginine, aspartic acid, asparagine, glutamic acid, isoleucine, leucine, phenylalanine, serine, threonine, and tyrosine were purchased from Sigma Chemical Co. (St Louis, MO, USA), glycine, histidine and valine from Merck,
Results and discussion
The finding of mutagenic activity in coffee similar to that of heterocyclic amines 14, 15, 16led us to search for probable precursors capable of forming mutagens in roasted coffee. Trigonelline is transformed into several volatile products when heated [20]and is one of the nitrogenous compounds in green coffee that could be a candidate for mutagen production. Others are amino acids, e.g. arginine, which has recently been shown to produce mutagenic activity when heated together with certain
Acknowledgements
X.W. is grateful to the Swedish Institute and the Education Committee of the P.R. China for a bilateral scholarship making her stay at the Lund University possible. The study was financially supported by the Swedish Cancer Society (1824-B95-14XAB), the Swedish Council for Forestry and Agricultural Research (50.0201/94) and the Swedish Nutrition Foundation.
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