What are sulphites and why are they used?

hat are sulphites and why are they used?

Sulfur dioxide (E220) and sulphites (E221 to E228) are used in the food industry as antimicrobial , anti- enzymatic and antioxidant preservatives . As such, they are used to inactivate mold , yeast and bacteria , as well as to preserve the color of foods and protect them from browning. Depending on the concentration, sulfur dioxide and sulphites can exhibit bacteriostatic (prevent the growth of microorganisms ) or bactericidal (cause their death) properties.
Sulfur dioxide is a gas and can be used as such or in liquid form, while sulphites appear as stable powders, strongly reactive in aqueous environment.

In common parlance, sulfur dioxide and some of its inorganic salts (sulphites, bisulfites and metabisulfites) used as additives for the preparation and preservation of food are grouped within the term sulphites :

  • E220 (Sulfur dioxide)
  • E221 ( Sodium sulfite)
  • E222 ( Sodium bisulphite)
  • E223 ( Sodium metabisulphite)
  • E224 ( Potassium metabisulphite)
  • E225 ( Potassium sulfite)
  • E226 (Calcium sulfite)
  • E227 ( Calcium bisulfite)
  • E228 ( Potassium sulphite acid).

Sulfur dioxide and sulphites in wine

Sulfur dioxide and sulphites are widely used to keep the color of fruit and vegetables intact , although the main and oldest application lies in the winemaking process. The sulphites – which once immersed in an acid solution release sulfur dioxide – have in fact the ability to inhibit the fermentation action of the yeasts present on the skin of the berries, which would give unwanted aromas to the wine.

After having inactivated these “wild” microorganisms, strains of selected yeasts are added to the must , insensitive to the action of sulphites and able to give the wine its sought-after aroma. Some of them even have the ability to generate them (which is why the presence of sulphites in wine and beer is anyway, a priori, a natural fact).

Before bottling, the wine can be treated again with sulphites to stop the fermentation processes and improve its conservation.


What are the foods rich in sulphites?

  • Wine (normally contains more white than red and sweet than dry)
  • Wine vinegar
  • Cider
  • Beer
  • Fruit juices
  • Jellies
  • Dehydrated fruit
  • Dried fruit(especially peeled fruit )
  • Candied fruit
  • Frosted fruit
  • Seafood
  • Shrimpsand other crustaceans
  • Cod fish
  • Preserved vegetables ( freeze-dried, dried , frozen, in oil , pickled , etc.)
  • Dried mushrooms
  • Raisins
  • Products made from meatsuch as hot dogs and hamburgers .

By law, the use of sulphites in meat foods is severely limited, as they significantly reduce the bioavailability of thiamine (vitamin B1).
Note : The ADI ( acceptable daily intake ) of sulfur dioxide was set at 0.7 mg / kg / day. In general in developed countries the daily intake does not exceed 20 mg.

Side effects

Reactions to sulphites: intolerance or allergy ?

Allergic reaction to sulphites

Sulphites are included in the list of the nine most common food allergens , even if the most common reaction of the body to these additives (which we will see more in the next paragraph) is not actually considered a real allergy. In fact, only a small slice of the population actually test positive for skin allergy with a clear involvement of the immune system ( IgE- mediated). However, anaphylaxis and other severe reactions are quite rare.

Intolerance to sulphites

In healthy individuals, at the doses commonly used in the food industry, sulfur dioxide is included in the list of active ingredients GRAS (Generally Recognized as Safe – Generally Considered Safe); it is in fact a natural compound, also produced by the body during the metabolism of certain amino acids and easily inactivated by detoxification systems endogenous (thanks to the enzymes sulfite oxidase which transform nell’innocuo sulfate).


Curiosity: Molybdenum Cofactor Deficit (MoCo)

The high sulphite content in the blood and urine of children can be caused by the so-called molybdenum cofactor deficiency (75% related to Sulfite Oxidase Deficit Encephalopathy ), which if left untreated can lead to neurological damage and early death. .

The treatment, which requires daily injections, has been made available since 2009.


Despite this safety of use, sulfur dioxide and sulphites can cause some problems, sometimes serious, to people who are so to speak “sensitive”. Sulfur dioxide , or sulfur dioxide, is a sharp, pungent-smelling gas that develops when sulfur is burned. Sulphites, for their part, react with acids developing sulfur dioxide, which has bleaching , bactericidal, but also highly irritating properties . However, it must be said that – once added to the food product – sulphites tend to combine irreversibly with some of its components, becoming largely inactive, therefore not subject to evaporation.
Contact of food sulphites with gastric acidityit generates a certain amount of sulfur dioxide, which is one of the most effective gases in inducing attacks of bronchospasm in asthmatics .
People allergic to aspirin are also particularly exposed to the risk of this type of reaction . In general, sulphites are estimated to cause problems in about 0.05-1% of the population (depending on the sources and dosages), with a significantly higher risk for asthmatic individuals (in which the prevalence can reach 5% ). In this context, the term sensitivity is used, since one cannot speak of a real allergy, but of an intolerance that triggers symptomspseudo-allergic, including the characteristic “head circle” (to which alcohol also contributes, often to a dominant extent ).

In addition to benign migraines , we must add the aforementioned risk of asthma attacks (bronchospasm), but also of hives , nausea , vomiting , intense sweating , hot flashes and hypotension . Symptoms usually occur within 15-30 minutes of ingestion.


Curiosity: Sulphite asthma

In 1986, after the identification of numerous cases of asthma induced by the consumption of sulphites contained in vegetables and fruit, the FDA (Food and Drug Administration) prohibited the use of these additives on fruit and vegetables intended for raw consumption; the only exception is the use of sulphites on minimally processed or ready-to- fry potatoes , where the use of sulphite is still permitted.


Due to the potential allergenic activity of sulphites and sulfur dioxide, food producers have been obliged for some years to declare the presence of these substances on the label ; in particular, this obligation applies when the concentration of sulfur dioxide in the food exceeds 10 mg / L or 10 mg / kg (result of the sulphites naturally present in foods added to those added). The food products that exceed this threshold will be subject to possible recall actions or punishment.


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