Sulphur dioxide

Sulphur dioxide (E220) is one of the oldest known food preservatives, with documented use in winemaking dating to ancient Rome. It acts through multiple complementary mechanisms: non-enzymatic and enzymatic browning inhibition, antimicrobial activity against bacteria and wild yeasts, antioxidant protection of sensitive flavour compounds, and protein binding that stabilises colour in dried fruits and wines. In aqueous solution SO₂ exists as a pH-dependent equilibrium of sulphur dioxide, sulphite (SO₃²⁻), bisulphite (HSO₃⁻), and metabisulphite ions, with bisulphite being the dominant antimicrobial species at typical food pH levels.

JECFA established an ADI of 0.7 mg/kg body weight per day for sulphur dioxide and sulphites (evaluated as SO₂ equivalents, 1999 evaluation). This ADI is significantly lower than most other preservatives, reflecting dose-dependent adverse effects in sensitive individuals. The European Food Safety Authority's 2016 re-evaluation (EFSA Journal 14:4438) confirmed the 0.7 mg/kg group ADI for SO₂ and sulphites (E220–E228). EFSA's exposure modelling showed that high-consuming children and some adult subgroups consuming wine, dried fruits, and preserved vegetables may approach or exceed the ADI, flagging a safety concern warranting consumption awareness.

Sulphite sensitivity affects an estimated 1% of the general population and up to 5–10% of people with asthma. Reactions range from mild urticaria and rhinitis to severe bronchoconstriction and, rarely, anaphylaxis. Regulatory bodies in the EU, US, Canada, and Australia require mandatory labelling when SO₂ or sulphite content exceeds 10 mg/kg or 10 mg/L — one of the few food additive disclosure thresholds written into allergy labelling law. Sulphur dioxide is approved under EU Regulation (EC) No 1333/2008 and US FDA 21 CFR §182.3862 with specific maximum use levels by food category.