Determination of N-nitrosodimethylamine in artificial gastric juice by gas chromatography-mass spectrometry and by gas chromatography-thermal energy analysis.

The thermal energy analyser (TEA) is considered to be the gold standard for the determination of nitrosamines. However, since many laboratories cannot justify the use of such a very specific detection system, alternative detection methods are useful. While standard gas chromatography (GC) detectors lack the selectivity of the TEA detector, mass spectrometry (MS) seems to be the method of choice to combine GC separation with mass selective detection. Moreover, the detection limits of the GC-MS assay in general use are about 4 times lower than those of the GC-TEA assay. A comparison of GC-MS and GC-TEA data on N-nitrosodimethylamine determinations showed a strong correlation between the two assays (R2 = 0.86), demonstrating the exchangeability of these methods.

Antimutagenic activity of green tea and black tea extracts studied in a dynamic in vitro gastrointestinal model.

An in vitro gastrointestinal model, which simulates the conditions in the human digestive tract, was used to determine potential antimutagenic activity of extracts of black tea and green tea. In this paper, results are presented on the availability for absorption of potential antimutagenic compounds present in tea and on the influence of the food matrix on this activity. Between 60 and 180min after the tea was introduced into the model, antimutagenic activity was recovered from the jejunal compartment by means of dialysis: the dialysate appeared to inhibit the mutagenicity of the food mutagen MeIQx in the direct plate assay with Salmonella typhimurium (Ames test). The maximum inhibition was measured at 2h after the start of the experiment and was comparable for black tea and green tea extract. To determine the influence of food matrices on the antimutagenic activity of tea, the model was loaded with black tea together with milk or a homogenized standard breakfast. The maximum inhibition observed with black tea was reduced by 22, 42 and 78% in the presence of whole milk, semi-skimmed milk, and skimmed milk, respectively. Whole milk and skimmed milk abolished the antimutagenic activity of green tea by more than 90%; for semi-skimmed milk the inhibition was more than 60%. When a homogenized breakfast was added into the model together with the black tea extract, the antimutagenic activity was completely eliminated. When tea and MeIQx were added together into the digestion model, MeIQx mutagenicity was efficiently inhibited, with green tea showing a slightly stronger antimutagenic activity than black tea. In this case, the addition of milk had only a small inhibiting effect on the antimutagenicity. Antioxidant capacity and the concentration of catechins were also measured in the jejunal dialysates. The reduction in antimutagenic activity corresponded with reduction in antioxidant capacity and with a decrease of concentration of three catechins, viz. catechin, epigallocatechin gallate and epigallocatechin. The in vitro gastrointestinal model appears to be a useful tool to study the antimutagenicity of food components.