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299-29-6
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Chinese name | Ferrous gluconate |
English name | Ferrous gluconate/Iron(II) gluconate |
Molecular formula | C₁₂H₂₂FeO₁₄ (Fe(C₆H₁₁O₇)₂) |
molecular weight | 446.15 (anhydrous), 482.18 (dihydrate) |
CAS number | 299-29-6 (dihydrate) |
Appearance | Yellowish-gray to pale yellowish-green powder—it darkens slightly after oxidizing in air. |
Solubility | Soluble in water (approximately 10 g/100 mL in cold water) – the aqueous solution is weakly acidic – it gradually oxidizes and changes color upon standing. |
Iron content | Approximately 11.6%~12.5% (as Fe) – one of the lowest among all mainstream food iron sources. |
smell | Extremely mild—with almost no metallic taste—and barely alters the milky flavor in dairy beverages. |
This is the largest application of ferrous gluconate in the food industry.
Food categories | Advantages of ferrous gluconate compared to other iron sources |
Milk and dairy beverages | The only iron source that can "disappear" in white liquids—it doesn't impart color or metallic taste. |
Infant formula milk powder | Mildest formula – not rejected by baby's taste buds + does not irritate the intestines + Infant Pure low chloride |
Blood sugar supplement syrup and oral solution | The solution is stable in brown bottles—the color is not jarring—and causes minimal stomach irritation. |
Fruit juices and functional beverages | Partial complexation in acidic liquids (pH 3-4) – delaying iron-catalyzed degradation of vitamin C. |
Breakfast cereals and cereal bars | The dry powder is stable—it has almost no taste after mixing—children won't notice it. |
Plant-based beverages (soy milk, oat milk) | Tasteless – does not interfere with the natural aroma of plant-based milk. |
It contains only 12% iron—why use it at all?
Ferrous sulfate has twice the iron content and costs only a fraction of the price—why does ferrous gluconate still have a market?
Because iron fortification isn't just about "stuffing iron into food." If iron ruins the color and taste of food—consumers won't buy it a second time. In milk and dairy beverages—ferrous sulfate is a "suicidal fortification"—its grayish-blue color and metallic taste kill the product faster than iron deficiency itself. Ferrous gluconate is "absent" in dairy beverages—that's the whole reason it's still used, even though it's much more expensive.
Like ferrous lactate (E585), it belongs to the iron sources approved by the EU for olive blackening. Fe²⁺ reacts with olive polyphenols to form a deep black iron-tannin complex—ensuring a consistent color in every canned black olive—it does not fade or turn brown. The limit is 150 mg Fe/kg.
In some other canned fruits and vegetables (such as certain bamboo shoots and bracken products), ferrous gluconate is also used as an auxiliary color-protecting agent to chelate metal ions that may catalyze oxidation and discoloration.
Trace amounts of Fe²⁺ play a role in the stabilization and hue adjustment of certain natural pigments—the mild reactivity of ferrous gluconate makes it suitable for use as a pigment auxiliary in this subcategory. For example, in the processing of dark-colored fruits such as blackcurrants and blackberries—trace amounts of iron salts can help stabilize the color of anthocyanins—preventing them from fading from deep purple to brown during storage.
Ferrous Gluconate (E579) is the ultimate champion of "gentleness" among food iron sources. It doesn't pursue the highest iron content (that's the domain of ferrous sulfate), nor does it pursue the lowest cost (that's the domain of elemental iron powder). What it pursues is—to be undetectable in white liquids, to be readily accepted in infant formula, and to ensure every olive is uniformly black in canned olives.
Scene | Why use ferrous gluconate instead of ferrous sulfate? |
Fortified milk | Ferrous sulfate turns milk grayish-blue—E579 |
Infant formula | The baby won't refuse—the stomach won't be irritated—chlorate is controlled to Infant Pure. |
black olives | Every single one is a uniform black—it won't fade or turn brown. |
Blood sugar replenishing syrup | The least uncomfortable stomach – most likely to complete a full course of treatment |
Gluconic acid is an oxidation product of glucose in human sugar metabolism—it is endogenous. When iron attaches to this organic acid anion that the human body is most familiar with—it gains all the necessary access to white milk, to a baby's taste buds, and to the matrix of polyphenols in black olives.
