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N-NITROSAMINES, INCLUDING N-NITROSOAMINOACIDS
TABLE 4.1.3 Concentrations of NDMA in beer from the German market. NDMA, g/kg Number of samples 158 401 454 72 175 87 71 580 13 Mean 2.7 0.28 0.44 <0.1 <0.1 0.1 0.1 0.1 0.15 Range <0.5 68 <0.5 9.2 <0.5 7 <0.2 1.3 <0.2 0.8 <0.2 1.0 <0.2 0.6 <0.2 1.7 <0.2 0.6 Year (Reference) 1977/78 (42) 1980 (45) 1981 (44) 1983 (46) 1984 (46) 1985 (46) 1986 (46) 1987 (46) 1989/90 (22)
smoked herring at 1600 g/kg NTCA (31). In samples of smoked oyster, concentrations of 167 g/kg NTCA and 109 g/kg NTHZ were reported (30). 4.1.2.1.3 Beer and Other Alcoholic Beverages In a publication by Spiegelhalder et al. (42), contamination of beer with N-nitrosamines was reported for the rst time. In 70% of 158 different beer samples tested, NDMA was identi ed at a mean concentration of 2.7 g/kg. The highest concentration found was 68 g/kg. Other N-nitrosamines like NDEA and NPYR were only found very rarely (17). Studies investigating the origin of this contamination unraveled that the contamination with N-nitrosamines arose during thermal treatment of the malt (kilning). Precursors of NDMA in malt are hordenin, gramine, and dimethylamine, the latter in concentrations of 5.5 12 mg/kg (15). Hordenin and gramine are naturally occurring alkaloids with a tertiary amine structure and are produced in barley during germination processes. Their nitrosation leads to the formation of NDMA. Gramine is converted more rapidly than hordenin; however, hordenin concentrations are higher (43). It has been found that the heating technique is of major importance. Heating the air in the kilning process by direct ring resulted in substantial higher amounts of NDMA in the malt (up to 1080 g/kg) compared with indirect heating using heat exchanger technology (44). In particular, gas burner ames operating at high temperatures (>1500 C) generate substantial amounts of nitrogen oxides from atmospheric nitrogen in the drying air. NOx react with the precursor amines in the malt and this entails markedly increased NDMA formation in the kiln. Modi cations in the ring technique (e.g., lower operating temperatures and indirect heating) reduced NOx generation and therefore NDMA formation (16, 22). Table 4.1.3 shows the trend of NDMA concentrations in beer in Germany from 1977 to 1990. A similar decrease of NDMA concentrations in beer was subsequently observed also in other countries (see Table 4.1.4). In the United States and Canada, a reduction of NDMA contaminations down to 1 5% of earlier levels has been reported by Scanlan and Barbour
CHEMISTRY, FORMATION, AND OCCURRENCE
TABLE 4.1.4 NDMA concentrations in beer in different countries. NDMA, g/kg Country United States/Canada France Sweden Spain Mean 0.074 0.23 0.1 0.11 Year (Reference) 1991 (47) 1991 (48) 1994 (49) 1996 (50)
(47). Although NDMA amounts in beer have been markedly reduced, consumption of beer still is a major factor with respect to the total dietary exposure with N-nitrosamines. Approximately 30% of the exposure via food results from the consumption of beer, contributing about 0.1 g of NDMA per person and day (20, 22). The daily uptake of NDMA resulting from the consumption of beer in France and Spain was estimated to be 0.02 00.03 g per person (48, 50). Other alcoholic beverages were also studied for contamination with volatile N-nitrosamines. Goff and Fine (51) examined wine, sherry, liqueur, gin, brandy, vodka, rum, and whiskey. Only the latter showed some NDMA contamination with concentrations between 0.3 and 3 g/kg. In a study by Walker et al. (52), the occurrence of volatile N-nitrosamines such as NDMA, NDEA, and N-nitrosodi-N-propylamine (NDPA) at low concentrations (<1 g/kg) in brandy and cider from France has been reported. In 11 out of 15 different whiskey samples examined, NDMA was found at concentrations up to 1.2 g/kg, whereas in wine, volatile N-nitrosamines were not detected (20, 22). 4.1.2.1.4 Milk Products and Cheese In general, only rather low concentrations of NDMA were found in cheese and powdered milk. In two of eight cheese samples, NDMA was detected at concentrations of 0.8 1.1 g/kg (22). This con rmed results from an earlier study with 200 cheese samples where a low contamination was reported (17). A single study reports the occurrence of NDBA (up to 1.7 g/kg) along with NDMA (up to 0.84 g/kg) in cheese from Italy. However, these ndings were not con rmed by other studies (53). In powdered milk, NDMA might be formed when direct drying processes are used (52). Studies by Sen and Seaman (54) reported a mean NDMA concentration of 0.4 g/kg in Canadian samples, whereas in two studies in Europe, only trace amounts of NDMA were found in milk powder (mean: 0.07 g/kg NDMA) (20, 22). In the United States, mean NDMA concentrations in milk powder products of 0.7 1.05 g/kg were reported (55). 4.1.2.1.5 Other Foods N-nitrosamines were also found in other foods processed by direct drying techniques, encompassing increased NOx exposure. Low amounts of N-nitrosamines (<1 g/kg, primarily NDMA) have been reported for instant coffee, infant formula, cocoa, powdered egg, and instant