Isotopic Labeling and LC-APCI-MS Quantification for Investigating Absorption of Carotenoids and Phylloquinone from Kale (Brassica oleracea)

The ability to study bioavailability of nutrients from foods is an important step in determining the health impact of those nutrients. This work describes a method for studying the bioavailability of nutrients from kale (Brassica oleracea var. Acephala) by labeling the nutrients with carbon-13, feeding the kale to an adult volunteer, and analyzing plasma samples for labeled nutrients. Results showed that conditions for producing atmospheric intrinsically labeled kale had no detrimental effect on plant growth. Lutein, β-carotene, retinol, and phylloquinone were analyzed using liquid chromatography−atmospheric pressure chemical ionization mass spectrometry. Analysis of plasma samples showed that labeled lutein peaked in plasma at 11 h (0.23 μM), β-carotene peaked at 8 (0.058 μM) and 24 h (0.062 μM), retinol peaked at 24 h (0.10 μM), and phylloquinone peaked at 7 h (3.0 nM). This method of labeling kale with 13C was successful for producing clearly defined kinetic curves for 13C-lutein,13C-β-carotene, 13C-retinol, and 13C-phylloquinone. Keywords: Carotenoid; β-carotene; lutein; retinol; vitamin A; phylloquinone; vitamin K; isotope; label; mass spectrometry; LC-MS; kale; Brassica oleracea