Speciation of essential nutrient trace elements in coconut water
Résumé
Coconut water (Cocos Nucifera) is shown to be a source of essential elements present in the form of low-molecular weight stable complexes known for their bio-availability. The total element concentrations were in the range of 0.2-2.7, 0.3-1, 3-14 and 0.5-2 ppm for Fe, Cu, Mn, and Zn, respectively, and varied as a function of the origin of the nut and its maturity. Speciation was investigated by size-exclusion chromatography-inductively coupled plasma mass spectrometry (ICP MS), and hydrophilic interaction liquid chromatography (HILIC)electrospray-Orbitrap MS. The metal species identified included: iron complexes with citrate and malate: Fe III (Cit) 3 (Mal), Fe III (Cit) 2 (Mal) 2 , Fe III (Mal) 2 , glutamine: Fe III (Glu) 2 and nicotianamine: Fe II (NA); copper complexes with phenylanine: Cu II (Phe) 2 and Cu II (Phe) 3 and nicotianamine: Cu II (NA); zinc complexes with citrate: Zn II (Cit) 2 and nicotianamine Zn II (NA) and manganese complex with asparagine Mn II (Asp) 2. The contributions of the individual species to the total elements concentrations could be estimated by HILIC-ICP MS.
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