Sulphites

Sulphites are a widespread group of preservatives and antioxidants used in foodstuffs (see below food additives), in the cosmetics and pharmaceutical industries and other branches of industry.

Chemical bases: Sulphites are the salts and esters of sulphurous acid (H2SO3, IUPAC nomenclature: dihydrogen sulphite). They form the water-soluble metabisulphites (pyrosulphites) by addition of sulphur dioxide. The esters of the sulphurous acid, also those with organic side ketene are also called sulphites. They are often used as preservatives in wine, dried fruit and potato products. In dried fruit products, sulphites inhibit non-enzymatic discolouration of the products. However, sulphites also occur naturally in almost all wines. Under acidic conditions sulphites and hydrogen sulphites release sulphur dioxide.

The use of sulfites in food (E 220-E224 and E 226-E228) is regulated in Europe by EU Directive EU No.95/2EC, in cosmetics by EU Regulation 1223/2009. The corresponding monographs are listed in the current European Pharmacopoeia (Ph.Eur. 8.0).

Sulphites in wine: The labelling "contains sulphites" or "contains sulphur dioxide" is obligatory according to the German wine law. The labelling obligation is based on the fact that sulphites play a role as allergens. The sulphite content of wines varies between 210 mg/l (red and rosé wine), 260 mg/l (white and rosé wine), 350 mg/l (Auslese) and 400 mg/l (Beerenauslese and Trockenbeerenauslese).

The etiopathological basis of the so-called sulphite intolerance has not yet been conclusively clarified.

Sulphur dioxide (SO2) and sulphite content of foodstuffs:

• salted dried fish (max. 200 mg/kg)
• Starch, sago, barley (maximum 50 or 30 mg/kg)
• Chips and other dried potato products (max. 50 mg/kg)
• white vegetables dried (max. 400 mg/kg) or frozen (max. 50 mg/kg)
• dried tomatoes (max 200 mg/kg)
• Dried fruits incl. nuts with skin (depending on the type of fruit max. 500 - 2,000 mg/kg)
• Meat, fish and seafood substitutes (max. 200 mg/kg)
• The use of sulphur dioxide and potassium sulphites (E 224, E 228) is widespread in wine production. Sulphur contents of more than 10 mg/l in the end product must also be indicated on wine labels.

Sulphur dioxide and sulphites are also used in cosmetics and as disinfectants in the food industry. Sulfur dioxide and foods containing sulfite must be labelled in the list of ingredients or on the label if they contain more than 10 mg/l or 10 mg/kg.

1. Häberle M et al (2016) Contact allergy to sulphites: clinical and occupational relevance - new data from DK and IVK. J Dtsch Dermatol Dermatol 14: 938-941
2. Jäger et al (2001) Food additives. In L. Jäger and B.Wüthrich food allergies and intolerances. Urban&Fischer p.177-192