Chapter 27
Nitrosamide Formation from Foodstuffs P. Mende, R. Preussmann, and B. Spiegelhalder
Downloaded by UNIV OF ROCHESTER on June 21, 2017 | http://pubs.acs.org Publication Date: March 28, 1994 | doi: 10.1021/bk-1994-0553.ch027
Department of Environmental Carcinogens, FSP03, German Cancer Research Center, Im Neuenheimer Feld 280, D-6900 Heidelberg, Germany
During a study on in vitro nitrosation of foodstuffs and analysis of the nitrosation products by gas chromatography combined with NO-specific chemiluminescence detection we observed the formation of an unknown nitroso compound from cocoa and dried tomatoes. The instability of this nitrosation product both under alkaline and acidic conditions together with its strongly acid-catalyzed formation indicated the presence of a volatile nitrosamide. Its structure was determined by mass spectrometry analysis as N-nitrosopyrrolidin-(2)-one (NPyrO).
When treated with 50 mM nitrite at pH 2, NPyrO forms up to 35 mg/kg from cocoa, coffee and coffee surrogates. Such high levels of nitrosamides have never been reported for nitrosated foodstuffs (1). At nitrite concentrations closer to physiological conditions the NPyrO formation strongly depends on the nitrite/ sample ratio due to nitrite scavenging activity of the sample. The presence of the NPyrO precursor pyrrolidin-(2)-one (PyrO) in food was shown using gas chromatography with nitrogen-specific chemiluminescence detection after conversion of PyrO into its trifluoroacetyl derivative. Only traces of PyrO were found in fresh food, but high amounts were detected in all dried samples (Table I). The increase in PyrO concentration does not correlate to the water loss during the drying process so it is evident that a reaction takes place which generates PyrOfroma precursor compound. 4-Aminobutyric acid probably is involved in this reaction since it is known to form PyrO under dehydrating conditions.
0097-6156/94/0553-O314$08.00/0 © 1994 American Chemical Society
Loeppky and Michejda; Nitrosamines and Related N-Nitroso Compounds ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
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M E N D E ET AL.
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Nitrosamide Formation from Foodstuffs
Using a test system specific for detection of nitrosamides which release nonpolar diazoalkanes (1) a nitrosamide-derived methylating activity was additionally detected in foodstuffs which contain caffeine (Table II). This activity has been reported previously in nitrosated Kashmir tea which is prepared by boiling tea leaves for several hours in the presence of sodium hydrogen carbonate (2). The slightly alkaline treatment (pH 7.5-8) results in hydrolysis of caffeine and formation of the nitrosamide precursors caffeidine and Â^iV-dimethylurea. However, the results from Table II indicate that a nitrosamide precursor is already present in the food sample and caffeine hydrolysis during boiling under alkaline conditions is not relevant for formation of the nitrosamide precursors). Furthermore, the concentrations of caffeidine (Table Π) and Af,N'-dimethylurea (< 0.7 mg/1) are too low to explain the methylating activity found in nitrosated beverages. Other relevant nitrosamide precursors therefore remain to be identified.
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Table I: Occurrence ofpyrrolidinone in foodstuffs pyrrolidinone (mg/kg) food item
average
fresh fruits / vegetable / meat / fish beer dried vegetables coffee surrogates coffee beans, instant coffee cocoa powder
0.1 1.5 22 36 40 55
range 0 0.3 5 30 29 32
-
0.4 4 48 41 50 77
Table II: Methylating activity due to unknown nitrosamides in nitrosated caffeinecontaining beverages (preparedfrom 50 g driedfood per liter). Nitrosation was done with 100 mM nitrite at pH 2 for one hour at 37°C. The methylating activity is compared to methylnitrosourea (MNU). Caffeidine was determined by gas chromatography/chemiluminescence detection (amine mode) after extraction with dichloromethane and derivatization with trifluoroacetic acid The methylating activity of Img caffeidine after nitrosation is equivalent to 0.002 mgMNU nitrosated sample
Kashmir tea (boiled with NaHC0 ) black tea black tea (boiled with NaHC0 ) green tea green tea (boiled with NaHC0 ) Mate tea coffee cocoa 3
3
3
methylating activity (mg/l, MNU equivalents)
caffeidine (mg/l)
3.0 2.4 2.1 1.5 1.7 4.4 2.1 0.6
0.1 0.3 0.2 0.5 0.4 0.2 0.3 0.4
Loeppky and Michejda; Nitrosamines and Related N-Nitroso Compounds ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
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NITROSAMINES AND RELATED JV-NITROSO COMPOUNDS
References: (1) Mende, P., Spiegelhalder, B. and Preussmann, R. (1991) Fd. Chem. Tox. 27, 475-478 (2) Kumar, R., Mende, P., Wacker, C.-D., Spiegelhalder, B., Preussmann, R. and Siddiqi, M. (1992) Carcinogenesis 13, 2179-2182
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R E C E I V E D January 26, 1994
Loeppky and Michejda; Nitrosamines and Related N-Nitroso Compounds ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
