Lee et al. (2019) measured Pb, Cd, As, and Al in Korean market oilseeds (sesame, perilla, flaxseed), noodles (wheat flour and sweet potato glass), and teas (black Sri Lankan, Korean green, Solomon’s seal), then compared raw versus processed forms to quantify migration rates. The central finding is that water-soluble heavy metals migrate significantly into cooking water or infusion liquid: boiling noodles transferred 14–46% of Pb, 20–68% of Cd, 10–30% of As, and up to 50% of Al into boiling water depending on cooking time, while oil extraction transferred much less (<10–33% to oil from seed). Tea infusion increased metal release with longer steeping time, with Al rising from 0.257 mg (2 min) to 0.556 mg (10 min) to 2.462 mg (30 min) per cup of Solomon’s seal tea.
Key numbers
Analytical method: ICP-MS (Dionex ICS5000+, Thermo Fisher) for Pb, Cd, As; ICP-OES (Optima 8300, PerkinElmer) for Al; microwave-assisted acid digestion. LODs: Pb 0.010–0.859 µg/kg, Cd 0.010–0.023 µg/kg, As 0.047 µg/kg; LOQs: 0.035–2.863 µg/kg. Recoveries from CRM: 71.5–107.5%.
Seed totals (per batch, all three extraction methods combined):
- Flaxseeds: Pb 0.758–36.0 µg/batch, Cd 0.133–2610 µg/batch (highest Cd), As 0.612–678 µg/batch
- Sesame: Pb 1.569–373.6 µg/batch, Cd trace to moderate, As 321–849 µg/batch (highest As)
- Perilla: highest Pb (557–936 µg/batch), moderate Cd and As
Seed-to-oil transfer rates:
- Pressing and solvent extraction: <10% transfer for Pb, As; <10–27% for Cd
- Supercritical CO₂ extraction: up to 30% transfer, significantly higher than pressing or solvent
Noodle boiling (50 g portion):
- Flour noodles raw: Pb 0.820 µg, Cd 0.714 µg, As 0.055 µg, Al 0.768 mg
- After 10 min boiling, Pb, Cd, As in noodle residue decreased significantly (p<0.05); Al residual 0.476 mg (38% reduction)
- Glass noodles: Cd not detected; Pb 0.634 µg raw
Tea infusion Al (Solomon’s seal tea, per cup):
- 2 min: 0.257 mg Al, 10 min: 0.556 mg Al, 30 min: 2.462 mg Al
- Green tea Al: 1.441 mg (2 min) to 1.957 mg (10 min) to 2.462 mg (30 min)
Methods (brief)
ICP-MS (Thermo Fisher Dionex ICS5000+) for Pb, Cd, As; ICP-OES (PerkinElmer Optima 8300) for Al, following microwave-assisted acid digestion. Three Korean market samples per food type (n=3 per matrix), tested in triplicate. Extraction methods: mechanical pressing, n-hexane solvent, and supercritical CO₂. Noodle boiling at 3/5/10 min intervals. Tea infusion at 2/10/30 min. Migration rates calculated by total mass transfer rather than concentration alone (to account for water volume changes). Limitation: small n per matrix (n=3); domestic Korean market only; no assessment of soil provenance or farming practice.
Implications
Certification: Directly relevant to product-category pages for cooking oils, noodles, and tea. The finding that boiling water concentrates metals removed from noodles means the relevant consumer exposure depends on whether cooking water is consumed (e.g., ramen broth vs. drained pasta). Tea infusion Al is a meaningful vector for Al exposure, particularly from herbal teas and Solomon’s seal. Supercritical CO₂ oil extraction extracts more heavy metals than pressing, which matters for certified oil products.
Courses: Strong real-world demonstration of the processing lever: discarding noodle cooking water or keeping tea infusion short reduces heavy metal intake meaningfully. Useful case study for QA/processing modules.
App: Processing method flag is warranted for oils (extraction method matters), noodles (consumed with vs. without boiling water), and teas (infusion time matters for Al in particular).