This Brazilian study measured iron and zinc in six common bean cultivars raw and after regular-pot or pressure cooking, with or without overnight soaking, analyzing grains and broth separately. Most zinc stayed in the cooked grains, with smaller amounts in the broth. Soaking changed zinc in cooked grains for three cultivars.
Key numbers
- Raw beans zinc 33.8 mg/kg (Jalo Precoce) to 43.1 mg/kg (BRS Grafite), dry basis (Table 2, p. 3).
- Cooked grain zinc 25.3 to 38.8 mg/kg and broth 0.8 to 16.1 mg/kg dry matter across cultivars and methods (Table 4, p. 4).
- BRS Grafite pressure-cooked grains 36.1 (soaked) and 38.8 mg/kg (unsoaked); grain plus broth 43.0 and 43.1 mg/kg (Results, p. 3).
- The authors cite labeling rules in which a food is a zinc source at 22.5 mg/kg (2.25 mg/100 g) and high in zinc at 45 mg/kg (Discussion, p. 5).
Methods (brief)
Beans were cooked 1:10 in deionized water in acid-washed pots; grains and broth were separated, dried, digested with nitric and perchloric acid and analyzed by ICP-OES in triplicate. Results are on a dry basis.
Evidence fitness
The study supports the point that home cooking keeps most bean zinc in the grain and that broth carries the rest, so eating grain with broth retains zinc. Values come from six research cultivars, not market beans.
Limitations
The printed standard deviations are garbled in the PDF text. Cultivars were supplied by a research program and may not reflect commercial beans. The labeling rule is cited without naming the jurisdiction.
Related evidence
Update history
No substantive edit history is available in this build. The full commit record is available in git.