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Processing and Bioavailability (WG2) page 72
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State-of-the-art: Summary
• For mass balance measurements, the ileostomy model is prefered. It offers
measurement of the absorption of any of the carotenoids (by difference between intake and
ileal loss), not confounded by microbial degradation of carotenoids which may occur in the
lower intestine. If performed with parallel blood sampling, ileal loss can be related directly to
the appearance of carotenoids in blood fractions. This provides data related to both carotenoid
absorption and metabolism. Such studies have been performed for β-carotene and are in
progress for lycopene (from food sources).
• Plasma Area Under the Curve may not be an appropriate method of measuring
carotenoid bioavailability, because of the probable re-export of carotenoid from the liver into
the plasma while absorption from the gut is still active.
For the plasma response to hydrocarbon carotenoids like β-carotene and lycopene, the use
of the triclyceride-rich lipoprotein (chylomocron) fraction offers the best prospect of
quantifying absorption, especially if the chylomicron fraction can be isolated from
contaminating VLDL. For the more polar carotenoids (xanthophylls) the chylomicron fraction
may not be appropriate, especially if they are not exclusively carried by the chylomicrons
when freshly absorbed.
Application of metabolic modelling techniques to plasma, and plasma fraction, response
curves provides a powerful tool for quantifying the kinetics of carotenoid absorption and
clearance to other tissue pools.
• Newer methods using stable isotopes indicate that they have the potential to permit
measurements of absolute absorption and subsequent metabolism in human subjects in the
presence of both dietary and endogenous carotenoids. Ideally, the use of stable isotope
labelled food materials coupled with the measurement of the isotopomers of the native
carotenoid and retinol in plasma fractions should provide the best possible measure of
bioavailability.