| Nitrite is commonly used in the process of cured meat products. The most important role of nitrite is to prevent the growth of Clostridium botulinum and to develop attractive cured color as well as flavor. However, safety threaten would be occur during the process. Nitrosamine in curing meat products has caused attention in many countries all over the world, with food safety having been an attention problem in society. By now, the study on the occurrence and formation of nitrosamines in meat products in China has been limited. Thus, it is of significant importance to study the mechanism of nitrosamine formation and control its production in these foods. In this paper, the contents of nitrosodiethylamine (NDEA) in cooked ham were determined by gas chromatography and high-resolution mass spectrometry. The effects of various factors on NDEA formation and the changes of its concentrations were also studied. The content and results are as follows:The effects of the initial nitrite levels, cooking temperature and cooking time on NDEA formation in cooked ham were studied. The changes of free amino acids concentrations and its correlation with the formation of NDEA were also analyzed.The results showed that the NDEA formation was highly correlated with the initial nitrite levels, nitrite contents after the curing and cooking process. NDEA was primarily formed during the cooking process, being absent with the curing procedure in 48h of curing time. With the increase of curing time, the concentrations of NDEA decreased while the contents of residual nitrite also decreased. Both the cooking temperature and time positively correlated with the formation of NDEA, indicating that cooking temperature and time were important factors affecting the formation of NDEA. The correlation analysis showed that the contents of amino acids of Aspartic acid, Glycin, Threoninie, Arginine, Alanine aas well as Tyrosine in cooked ham were positively correlated with the formation of NDEA (the correlation coefficient r were 0.6904, 0.7642, 0.7501, 0.7613, 0.7730 and 0.7224, respectively). However, Proline contents did not correlated well with NDEA concentrations, the correlation coefficient r being -0.1352 under p>0.05.The NDEA value of cooked ham at different cooking temperature was studied. The levels of NDEA gradually increased during the cooking process. The kinetics models of NDEA with respect to cooking time and temperature were developed. The first order reaction model and Arrhenius equation were used to describe the changes of NDEA contents as a function of the cooking temperature and time. Imitating the cooking conditions of cooked ham, L-Alanine was studied in the model system. The effects of temperature on nitrosation rate constant k were also studied. The results showed that with the increase of temperature, the reaction rate constant k significantly increased under p<0.05, reaching 13.01×10-2 at the temperature of 90℃. Studying the changes of contents of NDEA and residual nitrite in cooked ham with the addition of curing ingredients, sodium ascorbic and sodium phosphate were evaluated for their effects on NDEA and residual nitrite contents. Sodium ascorbic was found to be effective in reducing NDEA and nitrite residual contents. Sodium phosphate had a detectable accelerating effect on nitrite contents in cooked ham and subsequently increased NDEA levels.A further study was carried out to determine the effect of different storage conditions on residual nitrite and NDEA contents. With the increase of storage time, the concentrations of nitrite significantly decreased under p<0.05. Nitrite reduction at room temperature was more rapid than under refrigeration. The levels of NDEA gradually increased with the increase of storage time. The rate of the increase of NDEA at room temperature was more rapid than under refrigeration. After the storage of 72h, the NDEA concentrations in cooked ham added 200 mg/kg nitrite were 3.13 and 3.61μg/kg, repectively. However, in the case of storage at RT the changes in NDEA levels could be more the result of microbial action. During the storage, the residual sodium ascorbic changed little under p>0.05.
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