Production of intrinsically labelled spinach using stable isotopes (13C or15N) for the study of folate absorption

Labelling with stable isotopes is a powerful technique when used in metabolic studies. However, there is some doubt that absorption from a test meal labelled ‘extrinsically’ with a stable isotope compound will behave in the same manner as the same naturally occurring ‘intrinsically’ labelled compound. Three growing methods were investigated, and a method for growing spinach containing intrinsically labelled 5-methyltetrahydrofolic acid (5-CH3-H4-PteGlu) using as nutrient-flow hydroponic system and a nutrient solution containing 50% of the nitrate as 15N nitrate is described. The resulting plants contained 630 μg kg− 1 5-CH3-H4-PteGlu with 40% of the nitrogen present as 15N. After feeding, appearance of 5-CH3-H4-PteGlu in the plasma derived from the test meal could be identified by liquid chromatography/mass spectrometry.Industrial relevance: This paper deals with the highly relevant question of comparing the absorption of biochemicals – in this case folates – used as food fortificants or supplements with folates occuring naturally in foods. The authors provided data for the successful application of a method for growing spinach containing an intrinsic label for use in folate metabolism studies.