Sulfite

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To be distinguished from Sulfur trioxide.
A space-filling model of the sulfite anion.

Sulfites or sulphites are compounds that contain the sulfite ion SO32−. The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive,[1] its salts are widely used.

Structure[edit]

The structure of the sulfite anion

The structure of the sulfite anion can be described with three equivalent resonance structures. In each resonance structure, the sulfur atom is double-bonded to one oxygen atom with a formal charge of zero (neutral), and sulfur is singly bonded to the other two oxygen atoms, which each carry a formal charge of −1, together accounting for the −2 charge on the anion. There is also a non-bonded lone pair on the sulfur, so the structure predicted by VSEPR theory is trigonal pyramidal, as in ammonia (NH3). In the hybrid resonance structure, the S-O bonds are equivalently of bond order one and one-third.

Resonance structures of the sulfite ion

Evidence from 17O NMR spectroscopic data suggests that protonation of the sulfite ion gives a mixture of isomers:[1]

Bisulfite-equilibrium-2D.png

Commercial uses[edit]

Sulfites are used as a food preservative or enhancer. They may come in various forms, such as:[2]

Wine[edit]

Sulfites occur naturally in all wines to some extent.[3] Sulfites are commonly introduced to arrest fermentation at a desired time, and may also be added to wine as preservatives to prevent spoilage and oxidation at several stages of the winemaking. Sulfur dioxide (SO2, sulfur with two atoms of oxygen) protects wine from not only oxidation, but also from bacteria. Without sulfites, grape juice would quickly turn to vinegar.[4]

Organic wines are not necessarily sulfite-free, but generally have the lowest amount because no additional sulfites are added, as with most wines.[5] In general, white wines contain more sulfites than red wines, and sweeter wines contain more sulfites than dryer ones.[6]

In the United States, wines bottled after mid-1987 must have a label stating that they contain sulfites if they contain more than 10 parts per million.[5]

In the European Union an equivalent regulation came into force in November 2005.[7] In 2012, a new regulation for organic wines came into force.

Other foods[edit]

Sulfites are often used as preservatives in dried fruits, preserved radish, and dried potato products.

Most beers no longer contain sulfites. Although shrimp are sometimes treated with sulfites on fishing vessels, the chemical may not appear on the label. In 1986, the Food and Drug Administration in the United States banned the addition of sulfites to all fresh fruit and vegetables that are eaten raw.[8]

E numbers[edit]

E numbers for sulfites as food additives are:

E150b Caustic sulfite caramel
E150d Sulfite ammonia caramel
E220 Sulfur dioxide
E221 Sodium sulfite
E222 Sodium bisulfite (sodium hydrogen sulfite)
E223 Sodium metabisulfite
E224 Potassium metabisulfite
E225 Potassium sulfite
E226 Calcium sulfite
E227 Calcium hydrogen sulfite (preservative)
E228 Potassium hydrogen sulfite

Health risks[edit]

Sulfites are counted among the top nine food allergens,[dubious ] but a reaction to sulfite is not a true allergy.[9] Some people (but not many) have positive skin allergy tests to sulfites indicating true (IgE-mediated) allergy.[10] It may cause breathing difficulty within minutes after eating a food containing it,[11] asthmatics[12][13] and possibly people with salicylate sensitivity (or aspirin sensitivity)[14][15] are at an elevated risk for reaction to sulfites. Anaphylaxis and life-threatening reactions are rare.[10] Other symptoms include sneezing, swelling of the throat, and hives.[15]

In the U.S., labeling regulations do not require products to indicate the presence of sulfites in foods unless it is added specifically as a preservative;[8] however, many companies voluntarily label sulfite-containing foods. Sulfites used in food processing, but not specifically added as a preservative, are only required to be listed if there are more than 10 parts per million (ppm) in the finished product.

The products most likely to contain sulfites (fruits and alcoholic beverages less than 10ppm) do not require ingredients labels, so the presence of sulfites usually is undisclosed.

In 1986, the U.S. Food and Drug Administration banned the use of sulfites as preservatives on foods intended to be eaten fresh (such as salad ingredients).[8] This has contributed to the increased use of erythorbic acid and its salts as preservatives.[16]

In Australia and New Zealand, sulfites must be declared in the statement of ingredients when present in packaged foods in concentrations of 10 mg/kg (ppm) or more as an ingredient; or as an ingredient of a compound ingredient; or as a food additive or component of a food additive; or as a processing aid or component of a processing aid.[17]

Sulfites are widely used to extend the shelf life of products. Because it is often difficult to know whether a food contains sulfites, people may not realize they have a sensitivity to sulfites when they are having reactions to food or drinks. Sulfites are also known to destroy vitamin B1 (thiamin),[18] a vitamin essential for metabolism of carbohydrates and alcohol.

Metabolic diseases[edit]

High sulfite content in the blood and urine of babies can be caused by molybdenum cofactor deficiency disease which leads to neurological damage and early death unless treated. Treatment, requiring daily injections, became available in 2009.[19]

See also[edit]

References[edit]

  1. ^ a b Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 520. ISBN 978-0-13-175553-6. 
  2. ^ "Allergies: Sulfite Sensitivity". WebMD. 1 February 2007. Retrieved 2007-09-10. 
  3. ^ Zacharkiw, Bill, Montreal Gazette (July 15, 2008). "Can't hold the sulphites". 
  4. ^ "Sulfur in Wine Demystified". 
  5. ^ a b Breton, Félicien: Many organic wines contain sulfites
  6. ^ "Wine for Dummies" (McCarthy, Mulligan)
  7. ^ "Food Labeling - Community Legislation". European Commission. Retrieved 2007-09-10. 
  8. ^ a b c Fortin ND. Food Regulation: Law, Science, Policy and Practice.John Wiley and Sons, 2009, ISBN 0-470-12709-0, p. 288
  9. ^ "Sulphites - One of the nine most common food products causing severe adverse reactions". Canadian Food Inspection Agency. 
  10. ^ a b "SULFITE ALLERGY". The Australasian Society of Clinical Immunology and Allergy (ASCIA). 
  11. ^ California Department of Public Health: Food and Drug Branch. Sulfites
  12. ^ Cleveland Clinic. Sulfite Sensitivity
  13. ^ Gaynor D. Govias, BSc, BEd. American Academy of Allergy Asthma and Immunology. Sulfite Sensitivity
  14. ^ American Academy of Allergy Asthma and Immunology. Sulfites
  15. ^ a b World Health Organization. Preservative: Sulfur Dioxide and Sulfites
  16. ^ Hui YH. Handbook of Food Science, Technology and Engineering. CRC Press, 2006, ISBN 0-8493-9848-7, p. 83-32
  17. ^ "For asthma sufferers:the facts about sulphites in food". Food Standards Australia New Zealand (FSANZ). 
  18. ^ Dieu-Thu Nguyen-Khoa, MD and Dennis W Cope, MD, FACP. eMedicine. Beriberi (Thiamine Deficiency): Overview. May 20, 2008
  19. ^ Tedmanson, Sophie (November 5, 2009). "Doctors risk untried drug to stop babys brain dissolving". The Times (London). Retrieved May 13, 2010.