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7782-63-0
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Chinese name | Ferrous sulfate heptahydrate |
English name | Ferrous sulfate heptahydrate / Iron(II) sulfate heptahydrate |
Alias | ferrous sulfate, iron sulfate, and ferrous sulfate |
Molecular formula | FeSO₄·7H₂O |
molecular weight | 278.01 |
CAS number | 7782-63-0 |
Appearance | Blue-green monoclinic crystals or granules—the most vibrant color among food-grade iron sources. |
Solubility | Extremely high soluble in water (29.5 g/100 mL at 25°C), the aqueous solution is pale green, insoluble in ethanol. |
smell | Salty and astringent, with a strong metallic taste. |
Iron content | Approximately 19.8% (based on Fe) |
Oxidizing properties | Extremely strong – rapidly oxidizes in humid air (blue-green → yellow-brown Fe³⁺), catalyzing the oxidation of fats. |
Ferrous sulfate is the "gold standard" for iron fortification in food worldwide, but it faces unique challenges in every type of food:
Food categories | Advantages of ferrous sulfate | The problem of ferrous sulfate | Solutions for the food industry |
flour | Highest absorption rate – adding 3 mg of iron per 100 g of flour can significantly improve iron nutrition in the population. | Lipids oxidize and die within weeks; blue/brown spots form with polyphenols. | Shorten flour turnover cycle (mill to bakery < 2 weeks) + airtight and moisture-proof packaging |
bread | Baking at high temperatures does not destroy iron content | The bread crust developed grayish-blue stripes ("iron spots"). | Use dried ferrous sulfate (to reduce free water) + control the amount added. |
Breakfast cereal | Stabilization in high pressure extrusion puffing process | After puffing, the color of the flake cereal darkens. | Encapsulated/microencapsulated ferrous sulfate – released in the intestines, not oxidized in the cereal. |
Infant rice cereal | WHO-recommended iron source for infants and young children – high absorption, low risk | Blue-green spots cause panic among parents | Microencapsulation or replacement with ferrous fumarate (white) |
biscuit | Stable during long-term storage after baking (low moisture content) | It has almost no impact on flavor—the biscuits have extremely low moisture content, so the oxidation reaction is basically inhibited. | Using ferrous sulfate heptahydrate directly—biscuits are one of the few "problem-free" bases. |
Beverages and juices | Dissolves rapidly in liquid | Disastrous—it accelerates the degradation of Vitamin C within minutes, turning its color from orange to brown. | Ferrous sulfate is almost never used in liquid form—ferrous lactate or ferrous gluconate is used instead. |
core contradiction
Ferrous sulfate heptahydrate boasts the highest bioavailability—but it is also the strongest pro-oxidant. In the field of food iron fortification, there is an irreconcilable conflict between "good absorption" and "non-deterioration." Ferrous sulfate stands at the extreme of "best absorption," and the technological solutions to address it—encapsulation, microencapsulation, and shortening shelf life—are essentially paying the price for its "chemical properties."
To address the oxidation problem of ferrous sulfate, the food industry has developed a mature technical solution—microencapsulation.
FeSO₄ crystals → encapsulated with hydrogenated vegetable oil, maltodextrin, or ethyl cellulose → microcapsules
These microcapsules remain intact within a dry food matrix—the iron does not come into contact with the food. Only after entering the highly acidic environment of the stomach (pH 1-2) does the coating dissolve, releasing Fe²⁺, which is then absorbed by the intestines.
The cost of microencapsulation is increased cost—encapsulated ferrous sulfate is 3 to 5 times more expensive than the raw powder, and the coating itself accounts for 20% to 50% of the product weight (excluding the weight of the coating as iron), making the cost per unit of iron even higher. However, for high-end baby food and long-shelf-life cereals, this investment is necessary.
Ferrous sulfate in the food industry exists in two physical forms:
form | Fe content | color | stability | Applicable Scenarios |
Heptahydrate (FeSO₄·7H₂O) | ~20% | blue-green | Poor – it oxidizes rapidly in humid air. | High-moisture foods (not required if moisture content is visible to the naked eye). |
Dry ferrous sulfate (FeSO₄·xH₂O, x≈1~2) | ~30%~33% | grayish white | Better – lower moisture content → slower oxidation | Flour and bread fortification – almost entirely dry-type |
Tieyuan | Relative bioavailability | Effects on food color/taste | cost | Most suitable |
Ferrous sulfate (gold standard) | 100% (reference) | Extremely large – discoloration + oxidation + metallic smell | lowest | Flour, biscuits, and high-end packaging for short-term use |
Ferrous fumarate | ~70%~100% | Medium - relatively mild | Low-medium | Flour as a substitute for ferrous sulfate – white and less prone to discoloration. |
Elemental iron powder | ~10%~50% (depending on particle size) | Middle - Gray | Extremely low | Long shelf-life flour and cereal |
Ferrous lactate | ~100% | Small - Gentle | Medium-high | Baby formula and beverages – color- and taste-friendly alternatives |
Ferric pyrophosphate | ~30%~60% | Extremely small – white, insoluble | middle | Dry powder long shelf life food |
Ferrous sulfate's niche: It is the absolute king in the race for absorption rate - but kings have their price.
Ferrous sulfate heptahydrate is the "strongest single soldier" in the world of food iron fortification—everyone uses its bioavailability as a reference, but no one can ignore its ability to "disrupt" the food system.
Scene | What does ferrous sulfate do? | What do food engineers do? |
Fortified flour | The iron was absorbed—but the flour oxidized and spoiled after three weeks. | Replace the seven-water type with a dry type – shorten flour turnover to less than two weeks. |
Baby rice cereal | Iron was absorbed—but blue-green spots appeared in the rice flour. | Encapsulate ferrous sulfate in hydrogenated vegetable oil—it will only be released after being ingested. |
It is a "most effective but also most difficult to tame" source of iron. On a global public nutrition scale—when hundreds of millions of people need inexpensive iron with extremely limited budgets—ferrous sulfate's cost-effectiveness makes it an irreplaceable public health tool. A single ferrous sulfate tablet costing just a few cents is the WHO's classic prescription for iron-deficient populations worldwide.
But on the scale of the food industry—when a fortified bread needs to remain white and fresh on the shelf for seven days—every penny that food engineers spend on it is paying for its blue-green crystals and strong oxidizing properties.
