N-nitrosothiazolidine Research Articles

Volatile Nitrosamines in Fried Bacon

This study included 75 samples of traditionally produced pork bacon and 37 samples of 4 bacon-like products which were manufactured from turkey, beef, pork and turkey, and beef and turkey. All samples were purchased at commercial outlets in the United States, fried, and analyzed for volatile nitrosamines. Volatile nitrosamines detected included N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosodibutylamine (NDBA), N-nitrosopiperidine (NPIP), N-nitrosopyrrolidine (NPYR), and N-nitrosothiazolidine (NTHZ). All traditional pork bacon samples contained NPYR (mean 6.7 μg/kg, range 0.7−25 μg/kg), and all but one contained NDMA (mean 0.95 μg/kg, range none detected to 3.0 μg/kg). NPIP was detected only in samples which contained pepper. NDEA and NDBA occurred sporadically while NTHZ was detected rather consistently throughout the bacon samples. Overall, volatile nitrosamine levels detected in traditional pork bacon confirm the downward trend observed over the past several decades, although 16%...

N‐Nitrosothiazolidine and its 4‐Carboxylic Acid in Frankfurters Containing Alaska Pollock

ABSTRACTIn marine fish of the gadoid family trimethylamine oxide can decompose to formaldehyde. It can then react with cysteine and cysteamine, that may in turn react with nitrite, if present, to form N‐nitrosothia‐zolidine‐4‐carboxylic acid (NTHZC) and N‐nitrosothiazolidine (NTHZ). The NTHZC and NTHZ content of Alaska pollock surimi‐meat frankfurters were similar to or lower than those found in an all‐meat control, even at 50% substitution. No correlation was found between age of the fish protein prior to processing into surimi meat frankfurters and any measured variables.

Detection of a new nitrosamine, N-nitroso-N-methylaniline, and other nitrosamines in Icelandic smoked mutton

Varying levels (1-48 ppb) of N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), and a previously undetected nitrosamine, N-nitroso-N-methylaniline (NMA), were detected in Icelandic smoked mutton. Traces (0.6-2.4 ppb) of N-nitrosothiazolidine (NThZ) and low levels (56-475 ppb) of N-nitrosothiazolidine-4-carboxylic acid (NTCA), the two N-nitroso compounds commonly detected in smoked meats, were also present in such products. Evidence presented suggests that NMA in the meat is produced by the interaction of nitrite and smoke generated by burning sheep dung, the traditional source of fuel used for smoking such products. Nitrosation of laboratory-generated sheep dung smoke produced NMA, as well as NDMA and NPYR. The identity of NDMA, NPYR, and NMA was confirmed by mass spectrometry. It is suggested that the formation of all of the above nitrosamines in Icelandic smoked mutton can be minimized by changing or modifying the method of smoking.

Determination By Liquid Chromatography With Electrochemical Detection Of Cysteamine And Cysteine, Possible Precursors Of /V-Nitrosothiazolidine

A method is described that is selective, sensitive, rapid, and accurate for the quantitative measurement in meat products of both cysteamine and cysteine, potential precursors for N-nitrosothiazolidine (NTHZ) and N-nitrosothiazolidine-4-carboxylic acid (NTHZC), respectively. In general, a ground meat sample is homogenized with acetonitrile-formate buffer in the presence of dithiothreitol, and then is centrifuged, filtered, and recentrifuged in a disposable microfilter. The thiols are quantitated by liquid chromatography using an amperometric detector equipped with a gold/mercury electrode, operated in the oxidative mode. Cysteamine was found in 6 of 20 samples of raw pork belly in concentrations ranging from 150 to 450 ppb, and cysteine was found in all samples in concentrations ranging from 2.4 to 36.5 ppm. Analysis for the thiols and their corresponding nitrosamines--NTHZ and NTHZC--of bacon before and after processing showed no correlation between cysteamine and cysteine levels before processing nor with nitrosamine levels after processing. Liquid chromatography with electrochemical detection was found to be an extremely selective technique to measure the 2 free sulfhydryl compounds in a complex food substrate.

Inhibitory effects of thiols on a mutagenic contaminant from the synthesis of N-nitrosothiazolidine

The effect of S9 and various thiols were studied for potential modifying effects on a mutagenic trace artifact (‘NTHZ’) formed during the synthesis of N-nitrosothiazolidine (NTHZ) from cysteamine, formaldehyde and nitrite. Induced and uninduced S9 prepared from Syrian hamster livers reduced mutagenic activity in Salmonella TA100. Incorporation of boiled S9 into the preincubation medium produced similar effects, indicating a non-enzymatic mechanism for the detoxification reaction. Thiols alone also lowered revertant yields, and inhibitory efficacy was, in general, related to the p K a of the compound. At equimolar concentrations mutagenic activity was reduced in the following order (p K a values in parentheses): Thioglycolate (10.7) > mercaptoethanol (9.6) > reduced glutathione (8.8) > cysteine (8.35) > cystine (8.2). N-Acetylcysteine (9.52) and cysteamine (8.35), however, did not fit this pattern. The results of this study suggest that normal hepatic mechanisms may minimize ‘NTHZ’ genotoxicity thereby reducing potential health risks associated with its exposure.

An Investigation into Glucose as a Potential Precursor of N‐Nitrosothiazolidine in Bacon

ABSTRACTThe possible involvement of glucose in the formation of N‐nitrosothiazolidine (NTHZ) in bacon was investigated by pumping pork bellies with brines containing added glucose (2 and 4%). Raw bacon samples processed with glucose had significantly lower levels of N‐nitrosothiazolidine‐4‐carboxylic acid than the smoked control bacons. When the bacon samples with glucose were fried for 6 and 12 min, no NTHZ was detected in the fried products. N‐Nitrosopyrrolidine (NPYR) levels in these samples were much lower than those in the fried control samples. Results of this study demonstrate that the contribution of glucose to NTHZ formation in bacon is minimal relative to that of formaldehyde in the wood smoke.

Computer automated structure evaluation of the carcinogenicity of N-nitrosothiazolidine and N-nitrosothiazolidine 4-carboxylic acid

N-Nitrosothiazolidine-4-carboxylic acid (NTCA), a sulphur-containing nitrosamine present in human urine, was predicted to be non-carcinogenic by CASE, the newly developed Computer Automated Structure Evaluating system. On the other hand, N-nitrosothiazolidine (NTHZ), a nitrosamine present in food products, was predicted to be carcinogenic. The putative non-carcinogenic NTCA may be metabolized to NTHZ, a predicted carcinogen.

魚粉における揮発性ニトロサミンの存在および生成 ＩＩＩ 魚粉におけるニトロソチアゾリジンの生成機構

Both cysteamine (CysA) and thiazolidine (THZ) are considered to be the precursors of N-nitrosothiazolidine (NTHZ). Regarding the occurrence of these compounds in foods, how-ever, almost no data has been available so far. Present study has revealed the existence of about 200μg/kg of CysA in fresh sardine meat, while the CysA content in the meat de-creased below 30% of the initial level after being boiled, and only 5% of CysA was retained in the meal samples after freeze-drying of the boiled meat. On the contrary, very small quantity of THZ were detected in the fresh sardine meat, however, the contents remarkably increased upon boling to reach 128μg/kg, and the levels did not change even after lyophiliza-tion. Fish meal samples made from whole bodies of fresh sardines were found to contain larger amounts of THZ than those of CysA, in contrast; the THZ levels in the samples made from decomposed fish were appearently lower than those made from fresh materials. It was confirmed that nitrosothiazolidine-4-carboxilic acid (NTZC) was formed in the sardine meal samples after treatment with NO2 gas, and the yield of NTZC reduced by lowering the fresh-ness of raw fish materials. Based on the afbrementioned results, it may be proposed that the following two pathways exist in the formation of NTHZ in fish meal during manufacturing process, viz., (1) formation of NTHZ by nitrosation of THZ, and (2) formation of NTHZ by decarboxylation of NTZC.

Role of Lean Tissue on the Formation of N‐Nitrosothiazolidine in Raw Bacon

ABSTRACTLean tissue, separated from whole bacon, was found to contain the precursors for N‐nitrosothiazolidine (NTHZ), a nitrosamine formed when cured meats are smoked during processing. Of the various treatments investigated, cure incorporation of sodium ascorbate and liquid smoke yielded the lowest NTHZ values.

N-nitrosamines and residual nitrite in cured meats from the Dutch market.

A total of 140 samples of 16 kinds of cured meats were analyzed for contents of residual nitrite and N-nitrosamines. Nitrite was determined by reaction with sulfanilamide/naphthylethylenediamine and colorimetric measurement. N-nitrosamines were isolated from the samples by vacuum distillation and determined by gas-chromatography with chemiluminescence detection (GC-TEA). In six samples no nitrite was detectable (less than 1 mg NaNO2/kg), the remaining samples contained 1-140 mg NaNO2/kg, median value 6.8 mg/kg. In 46 samples (33%) no N-nitrosamines were detected, i.e. less than 0.1-0.5 microgram/kg of the individual nitrosamines, depending upon their structure. N-nitrosodimethylamine (NDMA) was the nitrosamine present most frequently, in 75 samples, contents were 0.1-0.9 microgram/kg, mean 0.3 microgram/kg. Other N-nitrosamines found were: N-nitrosopiperidine (NPIP), 10 times, 0.3-25 micrograms/kg; N-nitrosodiethylamine (NDEA), three times, 0.2-0.9 microgram/kg; N-nitrosopyrrolidine (NPYR), three times, 1.3-4.2 micrograms/kg; N-nitrosomorpholine, once, 0.7 microgram/kg and N-nitrosothiazolidine (NTHZ), 36 times, 0.5-91 micrograms/kg, mean 5.7 micrograms/kg. NTHZ was found most often and with the highest contents in smoked products. Frying of bacon and cured, smoked pork bellies led to substantially increased levels of NPYR in both products, and for the pork bellies also of NTHZ. In five samples of cured, smoked pork bellies after frying NTHZ-contents of 3.6-490 micrograms/kg (mean 179) were found. No correlation between residual nitrite levels and N-nitrosamine contents could be established. Investigations during the nineteen seventies gave much higher levels for NDMA, NDEA, NPIP and NPYR in Dutch cured meats than now found; at that time NTHZ was not measured.

魚粉における揮発性ニトロサミンの存在および生成 Ｉ 市販魚粉より検出された揮発性ニトロサミン

Volatile N-nitrosamines (VNA) in 32 commercial fish meal samples were analyzed by a gas chromatograph equipped with a thermal energy analyzer (GC-TEA), and three different VNA, N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR) and N-nitrosothiazolidine (NTHZ) were detected in these samples in common. The VNA levels were apparently varied depending on the method of preparation, particularly on the drying system of meals. The VNA levels in fish meals which had been dried by blowing hot air exhausted from an oil burner (direct heating-drying type) were found to be much higher than those dried by a steam heating drier system (indirect drying type). The reason for high levels of VNA in the meals prepared by direct heating-drying system might be associated with the higher NOX concentration in the heating air. As to the components of VNA in fish meal samples, the quantities of NDMA were the highest, followed by those of NPYR and NTHZ. The NDMA contents in the direct heating-drying type of fish meals were fairly high, and the maximum value was as much as 1400μg/kg. The mean value of NDMA in this type of meals was about 40times higher than that of NPYR, and 80times that of NTHZ. It was noted that carcinogenic N-nitrosomorpholine (NMOR) could he detected in two samples, although the migration route of morpholine, the precursor of NMOR, into these samples remained unclarified.

Effect of iV-Nitrosothiazolidine-4-Carboxylic Acid on Formation of N-Nitrosothiazolidine in Uncooked Bacon

N-Nitrosothiazolidine-4-carboxylic acid (NTHZC) was recently identified in a variety of smoked fish and cured meat products. While the toxicological properties of NTHZC are currently unknown, it has been speculated that N-nitrosothiazolidine (NTHZ) in fried bacon may be caused in part by decarboxylation of NTHZC. A limited survey of uncooked cured meat products failed to demonstrate any correlation between levels of NTHZC and NTHZ. However, NTHZC levels were significantly higher, ranging from 8 to 1400 ppb, than the corresponding NTHZ levels, which ranged from less than 2 to 18 ppb. Decarboxylation of NTHZC to NTHZ in a model system occurs at 110 degrees C, which is significantly higher than the average bacon processing temperature of 54 degrees C, but lower than the normal frying temperature of 177 degrees C recommended for bacon. Results from both model system and frying experiments with NTHZC and its precursors suggest that NTHZC decarboxylation to NTHZ is not the principal pathway to NTHZ formation in uncooked bacon.

Apparent mutagenicity of N-nitrosothiazolidine caused by a trace contaminant

The identification of N-nitrosothiazolidine (NTHZ) in smoked meat products prompted us to evaluate this compound for mutagenicity by the Salmonella assay. NTHZ was prepared in 99 + % purity by the nitrosation of the cysteamine-formaldehyde reaction mixture without isolation and purification of the resulting amine, and from thiazolidine, directly. Mutagenic activity was observed with TA100 without metabolic activation in the former, but not the latter preparation. An examination of the precursors, reaction intermediates, and HPLC separation of the NTHZ from the mutagenic product demonstrated that the genotoxic activity resulted from a synthesis-produced trace contaminant.

Mutagenicity of 2-hydroxyalkyl- N-nitrosothiazolidines

The mutagenicity of 2-hydroxyalkyl- N-nitrosothiazolidines was tested using Salmonella typhimurium strains TA98 and TA100. The N-nitrosothiazolidines tested were unsubstituted N-nitrosothiazolidine (NT), N-nitrosothiazolidine-4-carboxylic acid (NTC), 2-hydroxymethyl- N-nitrosothiazolidine (HMNT), 2-(1,2,3,4-tetrahydroxybutyl)- N-nitrosothiazolidine, 2-(1,2,3,4-tetrahydroxypentyl)- N-nitrosothiazolidine, 2-(1,2,3,4,5-pentahydroxypentyl)- N-nitrosothiazolidine (PHPNT) and 2-(1,2,3,4,5-pentahydroxypentyl)- N-nitrosothiazolidine-4-carboxylic acid. Among the N-nitrosothiazolidines tested, only HMNT and PHPNT exhibited clear dose-response mutagenicity toward strain TA100 with or without metabolic activation. None of the 2-hydroxyalkyl- N-nitrosothiazolidines were mutagenic to strain TA98. NT exhibited much stronger mutagenicity than either HMNT or PHPNT. Mutagenic activities of NT and PHPNT were eliminated by carboxyl substitution in the position α to the N-nitroso group.

N‐Nitrosothiazolidine in Cured Meat Products

ABSTRACTSince N‐nitrosothiazolidine (NTHZ) formation in cure‐pumped bacon has recently been linked to the heating‐smoking step in bacon processing, a survey of other smoked cured meat products was conducted, Nitrosothiazolidine was detected in 23 of 70 products, other than cure‐pumped bacon, in concentrations ranging from 1.7 ‐19.0 ppb. No correlation of NTHZ values with either residual sodium nitrite or with product type was found.

Factors Affecting the N‐Nitrosothiazolidine Content of Bacon

ABSTRACTThe analysis of raw and cooked bacon for the presence of N‐nitrosothiazolidine (NTHZ), a recently identified nitrosamine in bacon, indicated that the levels found were unrelated to residual nitrite or refrigerated storage. Raw bacon contained higher levels of NTHZ than either fried, baked, or broiled bacon. Since the total amount of NTHZ in whole raw bacon was higher than that found in fried bacon and its drippings combined, it was concluded that NTHZ was not formed during frying as is N‐nitrosopyrrolidine. The presence of NTHZ in bacon appears to be associated with smokehouse processing.

Dual Column Chromatographic Method for Determination of N-Nitrosothiazolidine in Fried Bacon

A dual column chromatographic procedure is described that permits the determination of N-nitrosothiazolidine (NTHZ), a newly identified nitrosamine, and N-nitrosopyrrolidine (NPYR), the principal volatile nitrosamine, in the same fried bacon sample. The procedure used an acid-Celite, Celite, sodium sulfate column followed by a partially deactivated basic alumina column to isolate NTHZ from bacon for subsequent quantitation by gas chromatography with a thermal energy analyzer (GC-TEA). A limited intralaboratory study gave standard deviations for repeatability and reproducibility of 1.20 and 1.55 ppb, respectively. The recovery of N-nitrosothiomorpholine, the internal standard added at the 10 ppb level, was 93.3 +/- 6.03%. The method is also free from artifactual nitrosamine formation.