Ferrous gluconate

Ferrous gluconate is the iron(II) salt of gluconic acid, used in food primarily as a colour retention agent in ripe olives and as an iron supplement in fortified foods. In black olive processing, it reacts with naturally occurring tannins in the olive flesh to fix a stable, uniform dark black colour that would otherwise fade or become uneven. Without this treatment, commercially processed ripe olives would show variable and unappealing coloration. It is also used in iron-fortified infant foods and nutritional supplements as a bioavailable iron source.

JECFA evaluated ferrous gluconate in 1965 and established an ADI of 0.8 mg/kg body weight per day, expressed as iron. This limit applies to the iron contribution of the additive, recognising that iron is an essential nutrient at low doses but can be harmful at high supplemental intakes. The ADI reflects careful balancing of beneficial nutritional effects and the potential for iron overload in susceptible individuals. Most consumers' dietary iron intake from ferrous gluconate in typical food applications falls within normal nutritional ranges.

Ferrous gluconate is approved in the EU as E579 and in other major jurisdictions for olive processing and food fortification. Consumers with hereditary haemochromatosis or other iron-overload conditions should be aware of iron contributions from fortified foods and may wish to limit intake of products with multiple iron-containing additives. For most people, ferrous gluconate in the context of olive colouring contributes negligible iron to the diet. As a nutritional supplement iron source it is generally well tolerated with a lower incidence of gastrointestinal side effects than ferrous sulphate, which is commonly noted in supplement literature.