Polycyclic aromatic hydrocarbons (PAHs) and dioxins are lipophilic organic pollutants occurring widely in the terrestrial environment. In order to study the PAHs and 2,3,7,8 TetraChloroDibenzo-pDioxin (TCDD) transfer in the food chain, pigs have been fed with milk mixed either with 14 Cphenanthrene, with 14 C-benzo[a]pyrene or with 14 C-TCDD. The analysis of portal and arterial blood radioactivity showed that both PAHs and TCDD were absorbed with a maximum concentration at 4-6 h after milk ingestion. Then, the blood radioactivity decreased to reach background levels 24 h after milk ingestion. Furthermore, the portal and arterial blood radioactivities were higher for phenanthrene (even if the injected load was the lowest) than these of benzo[a]pyrene or these of TCDD, in agreement with their lipophilicity and water solubility difference. Main 14 C absorption occurred during the 1-3 h time period after ingestion for 14 C-phenanthrene and during the 3-6 h time period for 14 Cbenzo[a]pyrene and for 14 C-TCDD. 14 C portal absorption rate was high for 14 C-phenanthrene (95 %), it was close to 33 % for 14 C-benzo[a]pyrene and very low for 14 C-TCDD (9 %). These results indicate that the three studied molecules have a quite different behaviour during digestion and absorption. Phenanthrene is greatly absorbed and its absorption occurs via the blood system, whereas benzo[a]pyrene and TCDD are partly and weakly absorbed respectively. However these two molecules are mainly absorbed via the portal vein.

Milk and yogurt constitute a major source of dietary protein. The nutritive value of dietary proteins is linked to subsequent postprandial amino acid availability in the portal blood (Rérat, 1988). Portal absorption of nutrients cannot be studied in humans, but pigs provide a valid model for studying protein digestion in humans (Rowan et al. 1994).Since stable isotopes are suitable to distinguish the exogenous from endogenous protein fraction in the intestinal lumen, intrinsic isotopic labelling of milk proteins has been considered a useful technique for nutritional investigations (Gaudichon et al. 1995; Gaudichon et al. 1999; Mahé et al. 1994). Recently, the use of 15N-labelled milk proteins were used to distinguish exogenous from endogenous N fractions in the human intestine after ingestion of 15N-milk or 15N-yogurt (Gaudichon et al. 1995). These authors pointed out that the jejunal flux of 15N was different for milk and yogurt. It is known that milk proteins and lactose undergo preliminary hydrolysis during lactic fermentation (Tamine & Deeth, 1980). It is also suggested that lactic fermentation enhances the nutritional value of milk proteins (Vass et al. 1984).

-The aim of this experiment was to study 15 N and amino-nitrogen (AN) portal absorption in the growing pig after ingestion of uniformly (0.2509 APE) labelled 15 N milk (M), yogurt ingested just after manufacturing (Y0), yogurt stored for 21 d at 4 °C (Y21) and heat-treated yogurt (HY). The highest porto-arterial differences (PAD) in 15 N and AN were found in the period between 30 min and 90 min after ingestion. The absorption of nitrogen from M and HY mainly occurred during the 0-120 min time period (about 70% for M and 67% for HY). For Y0 and Y21, a larger displayed absorption period over the 0-240 min time period was observed. Y0 and Y21 presented a quite similar portal absorption profile. The 15 N absorption rate was close to 80% for each studied milk product, suggesting that under our experimental conditions, dairy products (M, Y0, Y21 and HY) deliver nearly the same amounts of nitrogen to the organism. AN absorption rates were around 78% with a higher variability between the milk products. These results also indicate that most of the proteins were absorbed within the 240 min postprandial period.

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