Cardini et al. (2025) introduce a qualitative methodology combining size exclusion chromatography (SEC) coupled with ICP-MS/MS and SEC-QTOF-MS to identify cadmium-chelating compounds in seven plant-based food matrices. The study reports total Cd mass fractions in the matrices (by microwave digestion and ICP-MS) ranging from 9 to 570 µg/kg dry weight, with the lowest in basmati rice and the highest in beetroot leaves. The study’s primary contribution is analytical methodology for Cd speciation — identifying the molecular forms in which Cd is bound in plant foods (phytochelatins, phytic acid, flavonoids, and other ligands in the 1–20 kDa range) — with implications for future bioaccessibility studies.
Key numbers
Total Cd mass fractions (microwave digestion ICP-MS, µg/kg; values reported as range across 7 matrices):
- Range: 9 to 570 µg/kg dry weight
- Lowest: basmati rice (9 µg/kg)
- Highest: beetroot leaves (570 µg/kg)
- Other matrices tested: black-eyed beans, beluga lentils, tigernuts, sweet potato
Extraction recoveries (SEC fraction/total Cd):
- Range: 1.6% (sweet potato) to 72.3% (tigernuts)
- Basmati rice: among lowest recoveries (alongside sweet potato), suggesting strong Cd binding to matrix
- Tigernuts: highest recovery (72.3%), attributed to high fat content
- Relative standard deviations: 0.04 to 4.3% (triplicate analysis)
Cd molecular fractionation patterns:
- Distinct Cd-chelating patterns identified in the 1–20 kDa range across matrices
- High-molecular-weight (HMW, >20 kDa) compounds: 11.7% of Cd in beetroot leaves associated with HMW fraction
- Cd-chelating compounds identified: phytochelatins, phytic acid, tyrosine, coumaric acid, chlorogenic acid, myricetin, quercetin, phospho-D-glyceric acid, riboflavin
Certified reference materials validated: SRM-1572 citrus leaves (NIST), DORM-5 fish protein (NRC Canada).
Methods (brief)
Seven plant-based food matrices digested by microwave (HNO₃, 250°C, 20 min) for total Cd quantification by ICP-MS/MS (Agilent 8900, ¹¹⁴Cd, single quadrupole mode). SEC fractionation on two columns: Superdex 30 Increase (0.1–7 kDa range) and Superdex 200 Increase (10–600 kDa range). Mobile phase: 50 mM ammonium acetate. Elemental detection: SEC-ICP-MS/MS with oxygen reaction gas (mass-shift mode for P and S; on-mass for Cd, Ca, Zn). Compound identification: SEC-QTOF-MS for molecular formula determination of Cd-eluting fractions. Extraction optimization tested: time (30–60 min), organic solvents (acetonitrile 10–30%, methanol 10–30%) — organic solvents decreased Cd recovery.
Note: Total Cd values are in dry weight (DW). No wet weight values reported. Study is primarily a methods paper; occurrence data are incidental to the analytical development objective. Bioaccessibility data not yet available from this study.
Implications
Certification: Beetroot leaves at 570 µg/kg (DW) and legumes represent high Cd matrices in plant-based foods. The low extraction recovery of Cd from rice (strong matrix binding) may reduce bioaccessibility compared to matrices where Cd is more extractable, but this has not been directly tested.
Courses: Illustrates that Cd speciation (molecular form) in plant foods matters for bioaccessibility assessment and that matrix composition — protein content, starch, fat — drives extractability. Phytochelatins are a key Cd-binding mechanism in plant foods.
App: Basmati rice: Cd at low end (9 µg/kg DW). Beetroot leaves and leafy greens: Cd at high end (up to 570 µg/kg DW). Legumes (black-eyed beans, lentils): mid-range with moderate extractability.