E579 - iron gluconate

At a glance

• What it is: The ferrous (iron II) salt of gluconic acid, used as a food additive and iron source.
• What it does: Keeps the dark color of ripe black olives; can add iron to foods.
• Common foods: Canned ripe black olives; some iron-fortified drinks, cereals, and nutrition products.
• Safety: Allowed by regulators when used as directed; too much iron can be harmful.
• Also known as: Ferrous gluconate, E579.

Why is iron gluconate added to food?

Food makers use iron gluconate to stabilize the black color of processed ripe olives so they look uniform and do not turn brown in the can.¹ It is also used as a nutrient source of iron to fortify foods, since iron is an essential mineral.² “Ferrous” means iron in the +2 state, which is a form the body can absorb.

What foods contain iron gluconate?

• Canned ripe black olives often list iron gluconate on the label to keep their dark color.¹
• Some iron-fortified products, such as beverages, cereals, bars, and meal replacements, may use ferrous gluconate as the iron source.²
• Certain multivitamin and iron supplements also use ferrous gluconate, though supplements are labeled separately from regular foods.

What can replace iron gluconate?

• For black olives, a common alternative is ferrous lactate, which serves the same color-stabilizing role.
• For iron fortification, manufacturers can choose other iron compounds (for example, ferrous sulfate or ferric pyrophosphate), each with different taste and absorption profiles.
• In home cooking, there is no need to “replace” it—choose olives without color stabilizers or foods naturally rich in iron (like beans, meats, or spinach), depending on your preference.

How is iron gluconate made?

Iron gluconate is the ferrous salt of gluconic acid. It is typically produced by reacting gluconic acid (made by fermentation of glucose) with a suitable iron source under controlled conditions, then purified to meet food-grade standards.² In the European Union, it is listed as E579 with defined identity and purity specifications.³

Is iron gluconate safe to eat?

When used correctly, regulators consider iron gluconate safe for its approved uses. In the U.S., it is permitted as a color additive in ripe olives under good manufacturing practice limits.¹ In the EU, it is an authorized additive (E579) with official specifications that manufacturers must meet.³ As with all iron sources, overall iron intake matters; too much iron can be harmful, so total diet and any supplements should be considered.⁴

Does iron gluconate have any benefits?

As a fortificant, iron gluconate can help maintain adequate iron intake, which supports hemoglobin—the protein that carries oxygen in blood—and normal energy metabolism.⁴ The benefit depends on the product and the rest of the diet; not all foods using E579 are fortified (for example, olives use it for color, not nutrition).

Who should avoid iron gluconate?

• People with iron overload conditions (such as hereditary hemochromatosis) should avoid extra iron unless advised by a clinician.⁴
• Children should not consume high doses of supplemental iron; keep iron-containing products out of reach.⁴
• Anyone told by their healthcare provider to limit iron should review labels and avoid iron-fortified products.

Myths & facts

• Myth: It “dyes” olives black. Fact: It stabilizes the dark color of processed ripe olives; it is not a dye.
• Myth: All iron additives are the same. Fact: Different iron compounds vary in taste, solubility, and how well the body absorbs them.
• Myth: You can taste metallic flavors from it in all foods. Fact: At approved levels, most consumers do not notice any flavor change.

iron gluconate in branded foods

You’ll most often see E579 on the ingredient list of canned ripe black olives. It may also appear on nutrition shakes, bars, or cereals that are iron-fortified, and on some iron supplements labeled as ferrous gluconate. To check, read the ingredient list and any “iron” or “% Daily Value” lines on the Nutrition Facts panel.

References

Footnotes

1. Ferrous gluconate (color additive for ripe olives) — U.S. FDA, 21 CFR 73.160. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-A/part-73/subpart-A/section-73.160 ↩ ↩² ↩³

2. Ferrous gluconate (affirmed as GRAS; identity and use) — U.S. FDA, 21 CFR 184.1316. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-184/section-184.1316 ↩ ↩² ↩³

3. Specifications for E 579 ferrous gluconate — Commission Regulation (EU) No 231/2012. https://eur-lex.europa.eu/eli/reg/2012/231/oj ↩ ↩²

4. Iron Fact Sheet for Health Professionals — NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/ ↩ ↩² ↩³ ↩⁴