Potassium metabisulphite (potassium pyrosulphite)

Potassium metabisulphite, known by its code E224, is a crystalline powder that's either white or slightly yellow with a strong, sulfur‑like odor. This compound is a potassium salt derived from metabisulfurous acid and is commonly used in the food industry as a preservative and antioxidant. When dissolved in water, it releases sulfur dioxide (SO₂), which is effective at preventing microbial growth and oxidation, thereby extending the shelf life of various food products.

Origin:

Potassium metabisulphite is not found in nature; it's synthetically produced. The process involves reacting potassium hydroxide (KOH) with sulfur dioxide (SO₂) gas. This chemical reaction forms potassium bisulfite, which is then dehydrated to yield potassium metabisulphite.

Characteristics:

Here’s why potassium metabisulphite is widely used in the food industry:

• Preservative: Prevents the growth of mold, yeast, and bacteria.
• Antioxidant: Protects against oxidation, helping to maintain the colour and flavour of foods.
• Sterilizing Agent: Used to sterilize equipment in the production of wine and beer.
• Colour Stabilizer: Maintains the natural colour of fruits and vegetables.
• Solubility: Dissolves easily in water, which enhances its effectiveness.

Uses in Ultra‑Processed Foods:

Potassium metabisulphite plays several crucial roles in ultra‑processed foods:

• Dried Fruits: Prevents microbial growth and oxidation, extending shelf life. It also prevents browning, keeping the fruits visually appealing.
• Beverages (Wine and Beer): In wine, it sterilizes fermentation equipment and prevents oxidation and microbial spoilage during storage. In beer, it sanitizes brewing equipment and stabilizes the beverage by preventing unwanted secondary fermentation.
• Pickles and Sauces: Preserves colour and flavour by inhibiting microbial growth and oxidation, ensuring products remain fresh and tasty over time.
• Processed Meats: Prevents spoilage and rancidity by inhibiting the growth of harmful microorganisms and oxidation of fats.
• Fruit Juices: Maintains flavour and colour by preventing oxidation and microbial growth.

Health Considerations:

While generally recognized as safe, potassium metabisulphite does come with some health considerations:

• Allergic Reactions: Some people, especially those with asthma, may experience respiratory issues, skin rashes, or gastrointestinal distress.
• Sulphite Sensitivity: Individuals with sulfite sensitivity might suffer from headaches, dizziness, or severe reactions like anaphylaxis.
• Nutrient Interaction: Sulfites can destroy vitamin B1 (thiamine) in foods, potentially leading to deficiencies if consumed in large quantities.
• Gut Health: Sulfites, even at concentrations deemed safe for food, can inhibit the growth of four species of beneficial gut bacteria.
• Regulatory Limits: Regulatory bodies like the FDA and EFSA have established limits on the amount of potassium metabisulphite allowed in foods to ensure consumer safety.

References:

1. EFSA (European Food Safety Authority). "Sulfur Dioxide and Sulfites (E220 - E228) as Food Additives." EFSA Journal, vol. 16, no. 2, 2016.
2. FDA (U.S. Food and Drug Administration). "Overview of Food Ingredients, Additives & Colors." 2018.
3. Healthline. "What Are Sulfites? Why Are They in Our Food?" Accessed July 2024.
4. PubChem. "Potassium Metabisulfite." National Center for Biotechnology Information.
5. Irwin SV, Fisher P, Graham E, Malek A, Robidoux A. Sulfites inhibit the growth of four species of beneficial gut bacteria at concentrations regarded as safe for food. PLoS One. 2017 Oct 18;12(10):e0186629. doi: 10.1371/journal.pone.0186629. PMID: 29045472; PMCID: PMC5646858.