Determining the uptake efficiency of carotenes from vegetables.
Carotenes such as lutein and ß-carotene belong to a large group of health promoting compounds, since they function as antioxidants and as precursors of vitamin A. For nutritionists, it is important to know the efficiency by which carotenes are absorbed from the food matrix in the gastrointestinal tract after ingestion of vegetables. Sampling the plasma does not yield reliable information since the carotenes taken up are mixed with carotenes originating from other sources. Labelling vegetables with stable isotopes may help to solve this problem. Doses of stable isotope tracers that are used for clinical diagnostic and research purposes appear to be safe and without adverse effects (Koletzko et al, 1997).
Stable Isotope Solution: 13C-labelled vegetables
Vegetables can be cultivated from seed in hermetically closed phytotrons with 13CO2 as the solely source for carbon. The resulting uniformly 13C-labelled vegetables can be subsequently administered to volunteers in normal daily diets that may contain any other source of carotenes: the labelled carotenes can be easily distinguished from unlabelled endogenous pools. After consumption of the meals, plasma samples of the volunteers can be taken during a long period and the carotenes quantified using LC-APCI-MS techniques. The kinetics of the 13C-carotenes and their metabolites can thus be monitored. Uptake efficiency of lutein and ß-carotene was studied with these techniques using kale (Brassica oleracea var acephala) as vegetable (Kurilich et al, 2003; Novotny et al, 2005).
Figure 1 shows the 13C-lutein and 13C-ß-carotene concentration in the plasma during ca. 700 hour after administration of labelled kale to volunteers. The applied doses of both carotenes were almost equal, but the AUC (Area Under Curve) was three times greater for 13C-lutein (13.6 µmolar hr) than for 13C-ß-carotene (42.8 µmolar hr).
Figure 1. Concentration of 13C-lutein and 13C-ß-carotene in plasma after ingestion of 13C-labelled kale (Novotny et al, 2005).
The authors concluded that the results suggest that, although the absorption seems to be related, the bioavailability of lutein is much higher than that of ß-carotene. Isotopic labelling of kale gave them the opportunity to study the kinetics of lutein and ß-carotene without complications caused by existing endogenous pools.
Koletzko B, T Sauerwald, H Demmelmair. 1997.
Safety of stable isotope use.
European Journal of Pediatrics 156 (Suppl. 1): S12-S17 .
Kurilich AC, SJ Britz, BA Clevidence, JA Novotny. 2003.
Isotopic labeling and LC-APCI-MS quantification for investigating absorption of carotenoids and phylloquinone from kale (Brassica oleracea).
Journal of Agricultural and Food Chemistry 51: 4877 – 4883.
Novotny JA, AC Kurilich, SJ Britz, BA Clevidence. 2005.
Plasma appearance of labeled ß-carotene, lutein, and retinol in humans after consumption of isotopically labeled kale.
Journal of Lipid Research 46: 1896 – 1903.