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 h uman digestive tract, was used to determine potential antimutagenic activit y of extracts of black tea and green tea. In this paper, results are presen ted on the availability for absorption of potential antimutagenic compounds present in tea and on the influence of the food matrix on this activity. B etween 60 and 180 min after the tea was introduced into the model, antimuta genic activity was recovered from the jejunal compartment by means of dialy sis: the dialysate appeared to inhibit the mutagenicity of the food mutagen MeIQx in the direct plate assay with Sulmonella typhimurium (Ames test). T he maximum inhibition was measured at 2 h after the start of the experiment and was comparable for black tea and green tea extract. To determine the i nfluence of food matrices on the antimutagenic activity of tea, the model w as loaded with black tea together with milk or a homogenized standard break fast. The maximum inhibition observed with black tea was reduced by 21, 42 and 78% in the presence of whole milk, semi-skimmed milk. and skimmed milk, respectively. Whole milk and skimmed milk abolished the antimutagenic acti vity of green tea by more than 90%; for semi-skimmed milk the inhibition wa s more than 60%. When a homogenized breakfast was added into the model toge ther 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 sl ightly stronger antimutagenic activity than black tea. In this case, the ad dition 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 correspo nded with reduction in antioxidant capacity and with a decrease of concentr ation of three catechins, viz. catechin, epigallocatechin gallate and epiga llocatechin. The in vitro gastrointestinal model appears to be a useful too l to study the antimutagenicity of food components. (C) 2001 Elsevier Scien ce B.V. All rights reserved.