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Nitrosamines are a class of compounds with many carcinogenic members. They have been detected in cigarette smoke, rubber products and cosmetics and in many forms of cooked meat. Fried, grilled, barbecued and roasted meats are all susceptible to nitrosamine formation. These unwelcome compounds are formed by the reaction of nitrosating agents with amines. In the case of foods, the amines originate from the food proteins or might be present as free amines, but nitrosamine formation can be supplemented by a common food additive. Sodium nitrite is added to foods as a preservative and to enhance the colour and flavour of some foods but the nitrite group can act as a nitrosating agent. The EU has set the maximum level of sodium nitrite in processed meat to 150 mg/kg to limit nitrosamine formation but, in practice, about 120 mg/kg is usually added. The International Agency for Research on Cancer has classified some of the more commonly encountered nitrosamines. N-Nitrosodimethylamine (NDMA) and N-nitrosodiethylamine are probable carcinogens and N-nitrosodibutylamine, N-nitrosopiperidine and N-nitrosopyrrolidine (NPYR) are possible carcinogens. There have been many research studies on the formation of nitrosamines in meat and meat products. In one such study, a team of scientists from Belgium and Poland investigated the effects of some free amino acids on nitrosamine production in meats in the presence of nitrite and the free amino acids proline and hydroxyproline. Now, the team has extended the study to include a third amino acid, pyrrolidine. Gabriela Drabik-Markiewicz and colleagues from the Catholic High School Sint-Lieven, Ghent, the Free University of Brussels and the University of Silesia, Katowice, worked with fresh lean pork. The minced meat was injected with brine containing sodium chloride and pentasodium triphosphate then spiked with sodium nitrite and one of the three amino acids. The prepared food was cooked for 30 minutes at different temperatures to mimic industrial process: 85, 120 and 120-220°C for pasteurisation, sterilisation and baking/roasting, respectively. Cooked samples were spiked with N-nitrosodipropylamine as an internal standard and basified before vacuum distillation and extraction with dichloromethane. The dried extracts were analysed by GC with a thermal energy analyser as detector. This technique has proven to be one of the more popular for measuring volatile nitrosamines in preserved and cooked meats. The analytes were separated on a packed column. Under these conditions, all nitrosamines were baseline-separated and the detection and quantitation limits were 0.125 and 0.375 µg/mL, respectively. For cooked ham fortified with all three amino acids, only NDMA and NPYR were detected at levels up to 0.751 and 2.472 µg/mL, respectively. In fact, very few samples contained nitrosamines above the quantitation limit, so the team included those above the detection limit to give larger data sets, although "a relatively high number" of samples still had no detectable levels. The researchers recognised that this data collection technique introduced a high uncertainty but claimed that it was useful to allow the influential factors to be detected. The data sets from the three amino acids run at different nitrite concentrations and temperatures were subjected to ANOVA treatment. The presence of proline and pyrrolidine clearly increased the number of detections of NPYR from 12% to 35 and 88%, respectively, although hydroxyproline had no detectable effect. Pyrrolidine concentrations had a larger effect than nitrite concentrations. The highest NPYR level was observed after heating to 220°C or following the addition of 480 mg/kg of nitrite, well above EU legislative levels. In blank samples containing nitrite but no added amino acid, NDMA was detected more frequently than NPYR. NDMA formation was due principally to the addition of nitrite and, to a lesser extent, raised temperatures, and was limited when nitrite was added within the legal limits. Hydroxyproline and pyrrolidine increased NDMA levels to maximum levels of 0.654 and 0.751 µg/mL, respectively. This study has extended current knowledge of the effects of free amino acids on nitrosamine formation in cooked meat. Overall, higher nitrite levels and higher temperatures produced higher yields of NDMA and NPYR, the nitrite effect generally being the greater. However, nitrosamine formation was low for legal nitrite levels. Free amino acids increased the levels of nitrosamines, particularly pyrrolidine and proline for NPYR and, less markedly, hydroxyproline and pyrrolidine for NDMA. Related Links:
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