| Volatile N-nitrosamines are potential carcinogenic compounds which can induce tumors at various organs in various experimental animal species. And tumors induced in experimental animals resemble their human counterparts with respect to both morphological and biochemical properties. Extensive experimental and some epidemiological data suggest that humans are susceptible to carcinogenesis by N-nitrosamines and that the presence of these compounds in some foods may be regarded as an aetiological risk factor for certain human cancers including cancers of the oesophagus, stomach and nasopharynx. Therefore, great efforts have been made to investigate these compounds on formation and control in food. Especially, more efforts have been made to investigate meat product for N-nitrosamines because meat product is one of most important component in human food. Bacon and sausage are always used to be as materials to investigate volatile N-nitrosamines. However, there is little knowledge available in literature about volatile N-nitrosamines in dry-cured ham, which is a more complex meat system due to long ripening time. So the objective of this study is to investigate the formation and control of volatile N-nitrosamines in dry-cured Rugao ham.The research comprises four parts. First, study of the method for determination of volatile N-nitrosamines in dry-cured meat and investigation on styles and contents of volatile N-nitrosamines in Rugao ham which from market. Secondly, the changes of volatile N-nitrosamines and main physico-chemical indexes in Rugao ham during processing. Thirdly, study on the correlation between volatile N-nitrosamines and main physico-chemical indexes. The last is how to control volatile N-nitrosamines in Rugao ham during ripening and post-ripening. The results are as follows. 1. Method for determination of volatile N-nitrosamines in dry-cured meat and investigation on the style and content of volatile N-nitrosamines in Rugao hamThe effects of concentration by blowing with N2 at different temperature, concentration with K-D instrument at different temperature, extraction by liquid-liquid with DCM or by liquid-solid with active carbon, distillation by steam or vacuum on the recoveries of volatile N-nitrosamines, compare of once time steam-distillation and triple steam-distillation method to extract and purify the volatile N-nitrosamines in Rugao ham, using GC-MS to confirm the determination results by GC-NPD, sample preparation by solid phase micro-extraction (SPME) were investigated. The results show that the method which can be adopted to determination of volatile N-nitrosamines in dry-cured meat was consisted of following steps. First, a triple steam-distillation method was adopted to extract and purify the volatile N-nitrosamines. Secondly, volatile N-nitrosamines were extracted from water phase by liquid-liquid method with DCM. Thirdly, the DCM extraction mixture was dehydrated by Na2SCO4. Then, dehydrated DCM extraction mixture was concentrated by K-D instrument to about 10 mL, and the 10 mL concentrated mixture was concentrated again by N2 blowing to 1 mL. Following step was determination of volatile N-nitrosamines by GC-NPD and the last step was to use GC-MS to confirm the determination results by GC-NPN. Each recovery of this mothed for determining NDMA, NDEA, NPRY, NPIP, NDBA, NDHA is 68.12%,73.51%,65.26%,76.32%,70.78% and 56.42% respectively。And 3 volatile N-nitrosamines i.e. NDMA, NDEA and NPYR were found. Their contents were O.35μg/kg、1.42μg/kg and 6.75μg/kg respectively. Their detection rate was 100%,95% and 85% respectively.2. Change of volatile N-nitrosamines in Rugao ham during processingExperimental Rugao hams were processed according to traditional processing technology with 45 green hams weighted 8-9 kg. Approximately 600 g of muscle from the Biceps femoris and the around the muscles from 5 hams each time was obtained on 15 d,40 d,55 d,135 d,265 d and 325 d and then minced. Then volatile N-nitrosamines were determined with the method described above. The results showed that NDMA, NDEA and NPYR were found in Rugao ham during processing. And the content of NPYR was higher than those of NDEA and NDEA during processing. The contents of the 3 N-nitrosamines were all decreased during salting. Then the contents of NDEA and NPYR were still declined except that the concentration of NDMA increased during sun-drying. Following which, the contents of all volatile N-nitrosamines were all increased during ripening, and decreased during post-ripening. Most of the total volatile N-nitrosamine was produced during ripening.3. Change of physicochemical indexes of Rugao ham during processing and the correlation between physicochemical indexes and volatile N-nitrosaminesIn the above mentioned samples of Biceps femoris and the around the muscles, residual nitrite, biogenic amines, free amino acids, chloride, pH value, TVBN and certain oxidation indexes were investigated. And the correlations between volatile N-nitrosamines and physicochemical indexes of Rugao ham were analyzed with Pearson correlation coefficient method. The results showed that the general change trend of residual nitrite content was rising, but the trend of chloride was first down and then up. The change of TVBN was down during processing. The pH value was first up till end-sun-drying at which the value of pH was highest, and then began to be decreased. Tyramine, phenylethylamine, putrescine, spermine, tryptamine, cadaverine and spermidine were found in Rugao ham, and they were mainly produced during sun-drying and first stage of ripening. The general change trends of free amino acids were all up during processing and they were mainly produced during ripening.Carbonyl value, peroxide value and TBA value were gradually increased during salting and sun-drying. Then their values were decreased during first stage of ripening. Following which, their values were increased again during second stage of ripening but declined during post-ripening.There were some positive correlations between NDMA and peroxide value, TBA value. And there were some positive correlations between NDEA and NDMA, NPYR, free amino acids and TVBN, however, there were some negative correlation between NDEA and pH value, tyramine, putrescine, tryptamine, spermidine. There were also negative correlations between NPYR and pH value, phenylethylamine, spermine, tryptamine, spermidine, but positive correlations between TVBN and free amino acids.4. Effect of ascorbyl palmitate (AP) on the formation of volatile N-nitrosamines in Rugao hamExperimental Rugao hams were processed according to traditional processing technology with 90 green hams weighted 8-9 kg. Half of them were treated with 0.5 g of AP per kg green ham during the second salting, before treatment AP was mixed with crude salt. The other 45 green hams were used as control. Approximately 600 g of muscle from the Biceps femoris and the around the muscles from 5 hams each time was obtained on 15 d, 40 d,55 d,135 d,265 d and 325 d and then minced. Then volatile N-nitrosamines were determined with the method described above. The results showed that AP inhibited the formation of volatile N-nitrosamines and decreased the contents of chloride and residual nitrite. However, AP increased the contents of free amino acids and biogenic amines. Moreover, the effects of AP had abolished within a period.5. Effect of y-irradiation on the contents of volatile N-nitrosamines in Rugao hamExperimental Rugao hams were processed according to traditional processing technology with 60 green hams weighted 8-9 kg. Half of them were treated withγ-irradiation at a 5 kGy dose at end-sun-drying (55 d). The other 30 green hams were used as control. Approximately 600 g of muscle from the Biceps femoris and the around the muscles from 5 hams each time was obtained on 55 d,135 d,265 d and 325 d and then minced. Then volatile N-nitrosamines were determined with the method described above. The results showed thatγ-irradiation decreased the contents of NDMA, NDEA, NPYR, residual nitrite, tyramine, putrescine, spermine and free amino acids. However, y-irradiation increased the contents of spermidine, cadaverine, phenylethylamine and tryptamine. |
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