Surveillance of preservatives and their interactions in foodstuffs.

The organization of food surveillance in the UK is described, in particular as it has been applied to preservatives and their interaction products in foods. Applications of nitrates and nitrites as preservatives are discussed, together with the consequential exposure of consumers to these anions and their reaction products. Analytical methods for the determination of volatile and non-volatile N-nitroso compounds are referred to in relation to the results in food surveillance studies. Concentrations of Apparent Total N-nitroso Compounds (ATNC) averaged 2900 micrograms(N-NO)/kg in fried smoked bacon compared with 2400 micrograms/kg in fried unsmoked bacon; of this, known volatile and non-volatile N-nitroso compounds accounted for only 10-20%. ATNC were not detected in cheeses except those manufactured with added nitrate when ATNC levels up to 210 micrograms(N-NO)/kg were detected. Further studies are needed to determine the identity and toxicological properties of the non-volatile N-nitroso compounds.     

Examination of some fermented foods for the presence of apparent total N-nitroso compounds

The fermented foods yoghurt, bread and cheese were analysed for the presence of apparent total N-nitroso compounds (ATNC) by a group-selective procedure involving direct chemical denitrosation and chemiluminescence detection of the released nitric oxide. The levels of ATNC were below the 20 micrograms(N-NO)/kg detection limit in all 20 yoghurts, 23 of the 24 bread samples and 28 out of 31 different varieties of cheese analysed. ATNC were detected in most of those cheese samples manufactured with added nitrate, including Edam, Gouda and Havarti, in concentrations ranging from 30 to 210 micrograms(N-NO)/kg.     

Some nitrosoamino acids in bacon adipose tissue and their contribution to the total N-nitroso compound concentration

The levels of nitrosoamino acids and apparent total N-nitroso compounds in the adipose tissue of raw bacon have been examined. Nitrosoamino acids were detected in 80% of the samples in levels of up to 0.2 mg/kg. Apparent total N-nitroso compounds were present in all samples in concentrations of between 0.4 and 3.7 mg (N-NO)/kg. Nitrosoamino acids accounted for approximately only 1% of the apparent total N-nitroso compounds. The majority of the apparent total N-nitroso compounds in the adipose tissue were associated with the insoluble connective tissue fraction, with the remainder present as chloroform soluble species.     

An investigation of the levels of N-nitrosodimethylamine, apparent total N-nitroso compounds and nitrate in beer

Over 170 retail samples of beer have been analysed for N-nitrosodimethylamine (NDMA), apparent total N-nitroso compounds (ATNC) and nitrate. Levels of NDMA ranged from below 0.1 up to 1.2 micrograms/kg with a mean of 0.2 micrograms/kg. ATNC was detected in 42% of the samples in concentrations of up to 569 micrograms (N-NO)/kg. The levels of nitrate ranged from less than 0.2 up to 143 mg/kg with a mean of 16.8 mg/kg. There was no correlation between the amounts of NDMA and ATNC found in the retail beers. Samples taken during the course of fermentation showed that NDMA was unaffected by the bacterial reduction of nitrate which causes ATNC formation. HPLC studies using a photolysis/chemiluminescence detector revealed that the ATNC in beer are highly polar species of as yet unknown identity.     

Some nitrosoamino acids in bacon adipose tissue and their contribution to the total N-nitroso compound concentration

Zusammenfassung Der Gehalt an Nitrosoaminosäuren und ihr Anteil an den Gesamt-N-Nitrosoverbindungen im Fettgewebe von rohem Schinkenspeck wurde untersucht. In 80% der Proben wurde ein Gehalt an Nitrosoaminosäuren von bis zu 0,2 mg/kg festgestellt. Scheinbare Gesamt-N-Nitrosoverbindungen waren in allen Proben in einer Konzentration von 0,4 bis 3,7 mg (N-NO)/kg vorhanden. Die eigentlichen Nitrosoaminosäuren machen nur etwa 1% der scheinbaren Gesamt-N-Nitrosoverbindungen aus. Die Mehrzahl der scheinbaren Gesamt-N-Nitrosoverbindungen im Fettgewebe findet sich im nichtlöslichen Bindegewebe, wobei der verbleibende Rest chloroformlöslich ist.Summary The levels of nitrosoamino acids and apparent total N-nitroso compounds in the adipose tissue of raw bacon have been examined. Nitrosoamino acids were detected in 80% of the samples in levels of up to 0.2 mg/kg. Apparent total N-nitroso compounds were present in all samples in concentrations of between 0.4 and 3.7 mg (N-NO)/kg. Nitrosoamino acids accounted for approximately only 1 % of the apparent total N-nitroso compounds. The majority of the apparent total N-nitroso compounds in the adipose tissue were associated with the insoluble connective tissue fraction, with the remainder present as chloroform soluble species.

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Einige Nitrosoaminosäuren im fettgewebe von Schinkenspeck und ihr anteil an der Konzentration der Gesamt-N-Nitrosoverbindungen

     

The application of a chemical denitrosation and chemiluminescence detection procedure for estimation of the apparent concentration of total N-nitroso compounds in foods and beverages

The apparent total N-nitroso content of foods can be measured by a procedure based on chemical denitrosation and chemiluminescent detection of the eliminated nitric oxide. Procedures have been established which substantially reduce the 'apparatus blank' response to the denitrosating agent and allow total nitroso contents down to 10 micrograms (N-NO)/kg to be measured reproducibly on a 1-g sample. Typically, duplicate analyses of samples containing 10-1000 micrograms (N-NO)/kg differ by less than 15% of their mean. Potentially the method can be subject to some interference from compounds other than N-nitroso compounds, but at least in some commodities these interfering compounds do not exist in measurable amounts.     

A method for the investigation of free and protein-bound N-nitrosoproline in beer

Hydrolysis of beer peptides and proteins by both mild enzymatic and vigorous alkaline conditions has established that peptide-bound N-nitrosoproline residues are not present in beer in significant quantities. Free N-nitrosoproline remains the single most abundant identified N-nitroso compound, and this accounts for up to 10% of the apparent total N-nitroso compounds (ATNC). Both hydrolysis and extractability studies strongly indicate that the majority of the ATNC are not associated with beer peptides, but rather are likely to be low molecular weight possessing in some cases an acidic functional group.     

Tetrahydro-beta-carboline carboxylic acids in smoked foods.

This paper reports for the first time in smoked foods the presence of three tetrahydro-beta-carboline carboxylic acids. One of these, 1-hydroxymethyl-tetrahydro-beta-carboline-3-carboxylic acid, which is derived from the interaction of tryptophan and glycolaldehyde, and which has not previously been reported in foods, was observed in 20 samples at levels up to 444 micrograms/kg. The corresponding products which are derived from tryptophan and formaldehyde or tryptophan and acetaldehyde were found respectively in 28 samples at levels up to 22 mg/kg and in 16 samples at levels up to 881 micrograms/kg. Greater concentrations were generally found in those smoked foods having a lower pH value and produced by using a longer fermentation or maturation. Only 1-methyl-tetrahydro-beta-carboline carboxylic acid (156-574 micrograms/kg) was found in the four unsmoked samples analysed.     

BENZO(A)PYRENE IN SMOKED MEAT PRODUCTS

SUMMARY: A procedure was established for analyzing benzo(a)pyrene (BaP) in smoked meat products, which involves extraction, solvent partition, column chromatography and spectrophotofluorometric measurement. Studies were then made as to the effect of artificial casings on the content of BaP, penetration of BaP through a meat product in smoking, possible presence of the hydrocarbon in unsmoked meats and distribution of the compound after cooking smoked meat. Bologna was used in most experiments except for the one on cooking effect, in which bacon was used. Artificial cellulose casings caused a noticeable reduction in the concentration of BaP. Regardless of whether the smoke was generated in a small-scale or in a larger-scale generator, bologna smoked in casings had much less BaP than that smoked without casings. BaP was concentrated in the outer part of bologna. In smoking with or without casings, the hydrocarbon did not penetrate farther, in most cases, than 1.4–1.6 mm from the surface of the bologna. Several unsmoked meats of beef and pork were analyzed and none seemed to have endogenous BaP, since the detected amount was similar in magnitude to that of the solvent control. More than half the amount of BaP in smoked bacon was found in the fat drippings following cooking.     

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.     

The evaluation in the Ames test of the mutagenicity of tetrahydro-beta-carboline-3-carboxylic acids from smoked foods.

This paper reports the evaluation of five tetrahydro-beta-carboline carboxylic acids, formed from the interaction of woodsmoke carbonyls and tryptophan, for mutagenicity in the Ames test. Three of the compounds tested have been detected recently in smoked foods at levels in the micrograms/kg or mg/kg range. None of the compounds induced mutagenicity in TA 97, TA 98 or TA 100 strains of Salmonella typhimurium either with or without prior activation. However, tetrahydro-beta-carboline-3-carboxylic acid, and to a lesser extent 1-methyl-tetrahydro-beta-carboline-3-carboxylic acid were toxic to the strains of Salmonella typhimurium used. The inability of these beta-carbolines to induce mutation contrasts markedly with the mutagenicity of some beta-carbolines found in grilled meat products.     

麦芽和啤酒中的N-亚硝基化合物

N-亚硝基化合物属强致癌物质,有挥发性N-亚硝基二甲胺（NDMA）和非挥发性N-亚硝基化合物（ATNC）两种。啤酒中的NDMA主要来源于麦芽,在制麦工艺过程中形成;ATNC主要由微生物的硝酸还原反应产生。啤酒中的N-亚硝基化合物的分析检测方法有热能分析仪法、气相色谱法和HPLC法。（孙悟）     

N-Nitrosothiazolidine and N-Nitrosothiazolidine-4-Carboxylic Acid in Smoked Meats and Fish

Various smoked meats including raw and fried bacon and both unsmoked and smoked (uncured) fish were analyzed for NThZ and NTCA. Most meat samples, bacons, and a few smoked fish contained traces of NThZ and considerably high (up to 13,700 ppb) levels of NTCA. Preliminary results indicated that raw bacons processed by old-fashioned direct smoking methods contained the highest (> 1,000 ppb) level of NTCA. Formation of NThZ from the NTCA present in smoked bacon increased with an increase in frying temperature as well as with frying time. NTCA level in the raw bacon and the cooking conditions seemed to be the most important factors involved in the formation of NThZ in the fried bacon. The reason for finding only insignificant levels of NThZ in smoked fish could not be established conclusively.     

Incidence of some non-volatile N-nitroso compounds in cured meats

Procedures are described for the use of high-performance liquid chromatography and gas chromatography with a chemiluminescence detector in the analysis of N-nitrosoamino acids, N-nitrosothiazolidine-4-carboxylic acid, N-nitroso-oxazolidine-4-carboxylic acids and N-nitroso dipeptides N-terminal in N-nitrosoproline in cured meat products. The detection limit is around 5-10 micrograms/kg. Evidence is presented for the presence of all these species except the N-nitrosated dipeptides.     

DEVELOPMENT OF METHODS FOR THE CHARACTERISATION OF NON-VOLATILE N-NITROSO COMPOUNDS IN MALT

The effect of pH on extractability and the chromatographic separation of non-volatile N-nitroso compounds in aqueous wort extracts of malt have been studied. The apparent total N-nitroso compounds (ATNC) contain acidic functional groups and consist of a large number of minor components.     

Effect of the addition of nitrate to milk on the formation of volatile N-nitrosamines and apparent total N-nitroso compounds

 Saint-Paulin, a French semihard cheese, was manufactured from milk with and without added NO₃ ^–. Reference and experimental cheeses were analysed at different stages of ripening for the presence of apparent total N-nitroso compounds (ATNC) by chemical denitrosation and chemiluminescence detection (thermal energy analyser). The fate of NO₃ ^– and NO₂ ^–was also scrutinized. The levels of ATNC and of volatile N-nitrosamines were followed during ripening. After 60 days of ripening, ATNC were detected at concentrations of 27 μg NO-N/kg and 64 μg NO-N/kg in the cheeses obtained from milk with and without added NO₃ ^–, respectively. The NO₃ ^– contents of both cheeses were nearly the same, and below 5 mg/kg. The occurrence of NO₂ ^–was not observed. No relationship was found between the NO₃ ^– contents and the contamination of the cheeses by volatile N-nitrosamines. At the beginning of ripening, the cheeses manufactured with added NO₃ ^- showed high levels of ATNC (mean value 5800 μg N-NO/kg with large variations of 570–15210 μg NO-N/kg). These ATNC contents rapidly decreased during the first days of ripening (96%), but decreased much more slowly during the following days. An hypothetical mechanism, attempting to explain the disappearance of ATNC, involving the formation of alkylated species in the cheese was proposed. Received: 30 March 1998 / Revised version: 7 October 1998     

Characterization studies on insoluble total N-nitroso compounds in bacon adipose connective tissue

Enzymic hydrolysis was employed to solubilize 35% of the total N-nitroso compounds associated with bacon adipose connective tissue. Size exclusion chromatography of the digest showed that 95% of the solubilized N-nitroso compounds had molecular weights equivalent to those of di-, tri- and tetrapeptides. The likely identity of these compounds is discussed in the light of their extractability from acidified solution into ethyl acetate and their thermal and pH stability.     

烟熏工艺对熏肉挥发性风味物质的影响

以熏猪肉为对象,研究传统木熏工艺和现代液熏工艺对熏肉挥发性风味物质的影响。对其挥发性风味物质进行GC-MS分析,重点比较两种烟熏方式产品的特色挥发性风味物质的差别。结果表明,传统木熏工艺产品的挥发性风味物质在种类和数量方面都明显高于现代液熏工艺的产品,传统木熏工艺的产品检测出130种挥发性风味物质,而现代液熏工艺检测出121种,酚类物质作为烟熏产品的特色挥发性风味物质,传统木熏工艺的产品检测出15种,含量达到22.85%,而现代的液熏工艺的产品检测出14种,含量仅为7.87%。因此,传统的木熏工艺在风味方面仍然具有一定的优势。     

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

The 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.     

Nitrate, nitrite, and N-nitroso compounds in Finnish foods and the estimation of the dietary intakes

An estimate of the dietary intakes of nitrite, nitrate and N-nitroso compounds is presented, based on the analytical data supplied by the Finnish Food Quality Control. Figures on the food consumption of the Finnish population, taken from a national dietary survey, and food consumption of 1768 children and adolescents over a 48-h recall period were used. The mean daily dietary nitrate intakes were estimated to be about 55 mg for the total population and for children and adolescents. The mean nitrite intakes were 1.88 mg for the total population and 1.07 mg for children and adolescents. The intake of N-nitroso compounds (NDMA) was estimated to be 0.08 micrograms for the total population and 0.02 micrograms for children. Nitrates were found to originate mainly from vegetables (80%), nitrites from meat products (97%) and nitrosamines mostly from fish products and beer. A comparison of the estimate of dietary intake of with ADI values indicated that the nitrite intake of the total population was 23% and by children 39% of ADI. The average weight was approximately 60 kg for adults and 20 kg for children. When measured average weight (39 kg) was used, and the nitrite intake was found to be 28% of ADI. Nitrate intakes from food additives were 2.5% and 1.4% of the ADI value, respectively. When the total nitrate intake from various food sources was compared with the ADI (which is given only for food additives), the estimated nitrate intake of the total population was 25% and that of children 28% of the ADI value.