Sulphur dioxide ($SO_2$) and its related compounds, known collectively as sulphites, are chemical additives with a long history of use in food preservation, dating back to ancient Roman times. Their primary functions include inhibiting the growth of microbes like yeast, bacteria, and moulds, and acting as antioxidants to prevent food discoloration and spoilage. While generally recognized as safe for most people, these compounds can trigger adverse reactions in sensitive individuals, particularly asthmatics. Food manufacturers use various forms of sulphites, identified by E-numbers E220 to E228, which must be declared on product labels above a certain concentration threshold.
High-Concentration Food Sources
Certain food categories are well-known for containing high levels of sulphur dioxide and sulphites due to their preservative and anti-browning effects. For instance, sulphites are crucial for maintaining the colour of light-coloured dried fruits and preventing fermentation in wine.
Dried Fruits: Dried apricots, raisins, prunes, and other dried fruits are often treated with sulphites to preserve their colour and extend shelf life. Without treatment, apricots, for example, would turn dark brown.
Wine, Beer, and Cider: Sulphites are naturally produced during fermentation and are also added to prevent bacterial growth and oxidation, which can affect flavour. The phrase "contains sulphites" is a mandatory label on most wines.
Processed Meats: Sausages, deli meats, and pre-packaged burgers frequently contain sulphites to inhibit microbial spoilage and maintain freshness.
Processed Potatoes: Dehydrated, pre-cut, and pre-peeled potato products, such as frozen french fries and packaged mashed potatoes, often use sulphites to prevent browning.
Molasses: Sulphur dioxide has been used historically to preserve and lighten the color of molasses.
Other Significant Sources
Beyond these high-concentration items, many other processed and prepared foods also contain sulphites, often at lower levels. These can be easily overlooked but are important for sensitive individuals to recognize.
Condiments and Sauces: Products like ketchup, mustard, relish, horseradish, and various bottled sauces and salad dressings can contain sulphites.
Pickled and Fermented Foods: Vinegar, pickles, and sauerkraut use sulphites for preservation.
Fruit and Vegetable Juices: Bottled lemon and lime juices, as well as many fruit juice concentrates, use sulphites to prevent oxidation and spoilage.
Baked Goods and Snack Foods: Crackers, certain cereals, and snack foods, especially those containing dried fruit, may include sulphites.
Seafood: Fresh and frozen prawns are sometimes treated with sulphites to prevent black spot and maintain their appearance.
Glazed and Candied Fruits: Items like maraschino and glacé cherries, as well as other glazed fruit products, typically contain sulphites.
Comparing Sulphite Levels in Common Foods
It is important to understand that the concentration of sulphites varies significantly between different food categories. Regulations often dictate maximum permitted levels to ensure consumer safety. The following table provides a comparison of typical sulphite content (expressed as sulphur dioxide) based on various food regulations and analyses.
| Food Category | Typical Sulphite Level (mg/kg or mg/L) | Primary Reason for Use | Common Examples |
|---|---|---|---|
| Dried Fruits | High (>500) | Antioxidant, Anti-browning, Antimicrobial | Apricots, raisins, figs, prunes |
| Wine and Beer | Moderate (20-200) | Antioxidant, Antimicrobial | All types of wine, many beers and ciders |
| Bottled Juices | Low to Moderate (>10) | Preservative, Antioxidant | Lemon juice, lime juice, certain fruit concentrates |
| Processed Potatoes | Low to Moderate (>10) | Anti-browning | Frozen fries, dehydrated potatoes |
| Processed Meats | Low to Moderate (>10) | Antimicrobial, Antioxidant | Sausages, deli meats |
Conclusion: Navigating Sulphur Dioxide and Sulphites in Your Diet
For most individuals, sulphur dioxide and sulphites are harmless food preservatives. However, for those with an intolerance or sensitivity, particularly asthmatics, understanding and avoiding foods containing these compounds is critical for managing symptoms. A key strategy is to always check the ingredient labels of packaged foods, where sulphites must be declared by name or E-number if they exceed 10mg/kg or 10mg/L. Beyond packaged goods, it's wise to be aware of the high-concentration categories, such as dried fruits and wine, when dining out or selecting non-labeled items. Being a conscious consumer and knowing which products to question will empower you to manage your dietary needs effectively.
For a comprehensive list of regulated food allergens, including sulphites, consult the resources from regulatory bodies like the UK Food Standards Agency and Anaphylaxis UK.
