No abstract

Uncommon cis and trans fatty acids can be desaturated and elongated to produce unusual C18 and C20 polyunsaturated fatty acids in animal tissues. In the present study we examined the formation of such metabolites derived from cis and trans isomers of oleic and linoleic acids of partially hydrogenated vegetable oil origin in rats. For two months, adult male rats were fed a partially hydrogenated canola oil diet containing moderately high levels of trans fatty acids (9.6 energy%) and an adequate level of linoleic acid (1.46 energy%). Analysis of the phospholipid (PL) fatty acids of liver, heart, serum and brain showed no new C18 polyunsaturated fatty acids, except for those uncommon 18:2 isomers originating from the diet. However, minor levels (each < 0.3% PL fatty acids) of six unusual C20 polyunsaturated fatty acids were detected in the tissues examined, except in brain PL. Identification of their structures indicated that the dietary 9c,13t-18:2 isomer, which is the major trans polyunsaturated fatty acid in partially hydrogenated vegetable oils, was desaturated and elongated to 5c,8c,11c,15t-20:4, possibly by the same pathway that is operative for linoleic acid. Furthermore, dietary 12c-18:1 was converted to 8c,14c-20:2 and 5c,8c,14c-20:3; dietary 9c,12t-18:2 metabolized to 11c,14t-20:2 and 5c,8c,11c14t-20:4, and dietary 9t,12c to 11t,14c-20:2. These results suggested that of all the possible isomers of oleic and linoleic acids in partially hydrogenated vegetable oils, 12c-18:1, 9c,13t-18:2, 9c,12t-18:2 and 9t,12c-18:2 are the preferred substrates for desaturation and elongation in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

N-Nitroso-N-methylurea (NMU) is a highly potent direct-acting carcinogen that has been shown to induce cancer in a number of animal species. Although previous research has indicated that nitrosation of creatinine (CRN), a common constituent of meats, dried fish, and seafoods, can form traces of NMU, there is uncertainty as to (1) the yield of NMU and (2) whether detectable amounts of NMU can be formed from cured meats following nitrosation under acidic conditions given the low residual levels of nitrite found in cured meats at the present time. Lack of sensitive and specific analytical methods most likely has hindered progress in research in these areas. An HPLC postcolumn denitrosation-thermal energy analyzer technique and a GC-MS confirmation technique were developed for the determination of NMU in cured meats. Both techniques are highly sensitive (0.5 and 0.03 ppb, respectively) and specific. The optimum pH for NMU formation from CRN ranged between pH 1 and pH 3, and the yields of NMU under variable reactant concentrations ranged between 0.00004 and 0.0046%. When 27 samples of various cured meats (10 g aliquots each) were acidified with HCl (final pH values of 0.8-2.5) and incubated at room temperature for 2 h, without any additional nitrite, 24 gave results below detectable levels but 3 formed 2-26 ng of NMU/10 g of meat. Incubation of the negative meats with additional nitrite (50-500 microg/g of meat) formed 0.6-176 ng of NMU/10 g of sample. Although the amounts of NMU formed were extremely small, this seems to be the first reported formation of NMU from cured meats with and without additional nitrite.

A sensitive method was developed for the determination of deoxynivalenol (DON), nivalenol (NIV), alpha-zearalenol (alpha-ZEL), beta-zearalenol (beta-ZEL) and zearalenone (ZEN) in beer by capillary gas chromatography-mass spectrometry (GC-MS) of their heptafluorobutyrate (HFB) derivatives. Recoveries averaging 90-103% were obtained from beers spiked with each mycotoxin in the 5-20 ng/ml concentration range. Limits of detection were 0.1-1.5 ng DON/ml, 0.01-0.3 ng NIV/ml, 2.5-3 ng alpha- and beta-ZEL/ml, and 1.5-2 ng ZEN/ml. Twenty-nine of 50 samples of Canadian and imported beer surveyed were found to contain DON; of these nine contained greater than 5 ng/ml (up to 50 ng/ml). The identity of DON was confirmed by response ratios at m/z 670 and m/z 884 for the HFB derivative and m/z 497 and m/z 512 for the trimethylsilyl (TMS) derivative. NIV was also detected in three beer samples (0.1-0.84 ng/ml) but no alpha-ZEL, beta-ZEL or ZEN was found.

In continuation of our previous studies on N-nitroso-N-methylurea (NMU) formation in cured meats following incubation with nitrite at gastric pH, we extended the investigation to other foods mentioned in the title of this paper. The main objective was to determine whether these foods have the potential to form NMU at pH's that can be found in the human stomach. This was done by nitrosating an aliquot (5 g for fish sauce, 10 g for the others) of each with 7.25 microM to 1.59 mM levels of sodium nitrite for 2 h at room temperature at pH 0.8--1.5 and measuring the amounts of NMU formed. Of the samples tested, fish sauce formed 2--712 ng of NMU, followed in decreasing order by herring (<0.3--688 ng); dried anchovy, shrimp, and other fishes (<0.3--134 ng); crab and lobster paté (<0.3--342 ng); sardines (6--59 ng); oysters and mussels (11--31 ng); dried squid (3--47 ng); kimchi (7--107 ng); and Japanese pickled radish (<0.3--72 ng). Incorporation of 200-2000 ppm of ascorbic acid in the fish sauce and other foods, prior to nitrosation, appreciably inhibited such NMU formation. Although previous researchers in China reported NMU formation in nitrosated samples of fish sauce, this is the first reported formation of NMU upon nitrosation of the other foods mentioned above, and the first reported inhibition of such formation by added ascorbic acid.