E224 (Potassium metabisulphite) is a chemical compound that belongs to the sulphite group, sulphur-based components that release sulphur dioxide SO₂, an active preservative compound, a white granular powder.

E224 is a food additive known as potassium metabisulfite. 

The name describes the structure of the molecule:

•  The letter E followed by a number is a coding system used in the European Union to identify food additives approved for use in food. These additives are tested for safety and are listed with an "E" code followed by a unique number.
• 224 is the specific identifier for potassium metabisulfite. This compound is used as a preservative and antimicrobial agent in various food products.  The E200 series (E200-E297) lists preservatives and a few decolorizers, mostly chemical.

Potassium metabisulphite

The name defines the structure of the molecule

• "Potassium" is an alkali metal, symbol K, with atomic number 19. It's an essential element for life and plays a key role in regulating blood pressure and cellular functions.
• "Metabisulphite" indicates the presence of a metabisulphite anion. It is a food additive and a preservative agent.

Description of raw materials used in production

• Sulfur Dioxide (SO₂) - Gas used in the production of sulfites.
• Potassium Hydroxide (KOH) - Strong base used to neutralize the formed sulfurous acid.

Step-by-step summary of industrial chemical synthesis process.

• Production of SO₂ - Burning of sulfur produces sulfur dioxide (SO₂).
• Reaction with KOH - Sulfur dioxide (SO₂) reacts with potassium hydroxide (KOH) to form potassium bisulfite (KHSO₃).
• Oxidation - Potassium bisulfite is then oxidized to form potassium metabisulfite (K₂S₂O₅).
• Crystallization - The potassium metabisulfite solution is cooled to allow crystallization.
• Filtration - Crystals are separated from the solution by filtration.
• Drying - Moisture is removed from the crystals.
• Quality Control - The final product undergoes various quality checks to ensure it meets specifications.

The sulphite group includes:

What it is used for and where

It is used in the food sector as preservative and antioxidant and is labeled in Europe with the number E224 in food additives.

Can give allergy.

Most significant studies:

It is added to winesas preservative  and appears on the label as "Sulfites", in vegetables and dried fruit and dried fruit, mushrooms and in many food products to increase the storage time (1).

It is also used to obtain better sensory qualities to foods (2).

In addition to essential oils, potassium metabisulfite (KMS) may be useful as a repellent for Drosophila suzukii,  a globally invasive pest of soft-skinned fruit (3).

Safety

Symptoms related to sulphite sensitivity can be of varying nature and importance. The most common are headache and generalised itching or swelling, but cases of nausea, bronchoconstriction, diarrhoea, hypotension and shock have also occurred (4).

EFSA's Scientific Panel on Food Additives and Flavourings assessed the risk for toxic elements in sulphur dioxide (E 220-228), based on data submitted by stakeholders, and concluded that the EU specification maximum limits for arsenic, lead and mercury should be lowered and a maximum limit for cadmium should be introduced (5).

Sodium Sulfite, Ammonium Sulfite, Sodium Bisulfite, Potassium Bisulfite, Ammonium Bisulfite, Sodium Metabisulfite, and Potassium Metabisulfite are inorganic salts that function as reducing agents in cosmetic formulations. All except Sodium Metabisulfite also function as hair-waving/straightening agents. In addition, Sodium Sulfite, Potassium Sulfite, Sodium Bisulfite, and Sodium Metabisulfite function as antioxidants. Although Ammonium Sulfite is not in current use, the others are widely used in hair care products. Sulfites that enter mammals via ingestion, inhalation, or injection are metabolized by sulfite oxidase to sulfate. In oral-dose animal toxicity studies, hyperplastic changes in the gastric mucosa were the most common findings at high doses. Ammonium Sulfite aerosol had an acute LC(50) of >400 mg/m(3) in guinea pigs. A single exposure to low concentrations of a Sodium Sulfite fine aerosol produced dose-related changes in the lung capacity parameters of guinea pigs. A 3-day exposure of rats to a Sodium Sulfite fine aerosol produced mild pulmonary edema and irritation of the tracheal epithelium. Severe epithelial changes were observed in dogs exposed for 290 days to 1 mg/m(3) of a Sodium Metabisulfite fine aerosol. These fine aerosols contained fine respirable particle sizes that are not found in cosmetic aerosols or pump sprays. None of the cosmetic product types, however, in which these ingredients are used are aerosolized. Sodium Bisulfite (tested at 38%) and Sodium Metabisulfite (undiluted) were not irritants to rabbits following occlusive exposures. Sodium Metabisulfite (tested at 50%) was irritating to guinea pigs following repeated exposure. In rats, Sodium Sulfite heptahydrate at large doses (up to 3.3 g/kg) produced fetal toxicity but not teratogenicity. Sodium Bisulfite, Sodium Metabisulfite, and Potassium Metabisulfite were not teratogenic for mice, rats, hamsters, or rabbits at doses up to 160 mg/kg. Generally, Sodium Sulfite, Sodium Metabisulfite, and Potassium Metabisulfite were negative in mutagenicity studies. Sodium Bisulfite produced both positive and negative results. Clinical oral and ocular-exposure studies reported no adverse effects. Sodium Sulfite was not irritating or sensitizing in clinical tests. These ingredients, however, may produce positive reactions in dermatologic patients under patch test. In evaluating the positive genotoxicity data found with Sodium Bisulfite, the equilibrium chemistry of sulfurous acid, sulfur dioxide, bisulfite, sulfite, and metabisulfite was considered. This information, however, suggests that some bisulfite may have been present in genotoxicity tests involving the other ingredients and vice versa. On that basis, the genotoxicity data did not give a clear, consistent picture. In cosmetics, however, the bisulfite form is used at very low concentrations (0.03% to 0.7%) in most products except wave sets. In wave sets, the pH ranges from 8 to 9 where the sulfite form would predominate. Skin penetration would be low due to the highly charged nature of these particles and any sulfite that did penetrate would be converted to sulfate by the enzyme sulfate oxidase. As used in cosmetics, therefore, these ingredients would not present a genotoxicity risk. The Cosmetic Ingredient Review Expert Panel concluded that Sodium Sulfite, Potassium Sulfite, Ammonium Sulfite, Sodium Bisulfite, Ammonium Bisulfite, Sodium Metabisulfite, and Potassium Metabisulfite are safe as used in cosmetic formulations (6).

"Sulphites studies"

Molecular Formula  K₂S₂O₅ or K₂O₅S₂

Molecular Weight   222.312 g/mol

UNII  65OE787Q7W

CAS  4429-42-9  16731-55-8

EC Number 240-795-3

Synonyms :

• Potassium metabisulfite
• Dipotassium disulfite
• Dipotassium pyrosulfite
• Dipotassium disulphite
• Dipotassium metabisulfite
• E224
• Potassium disulfite
• Potassium pyrosulfite
• Disulfurous acid, potassium salt (1:2)
• Potassium metabisulfite (NF)