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Sulfite
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Sulfites (also sulphites) are compounds that contain the sulfite ion SO32- (IUPAC name sulfate(IV) ion).
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.
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Encyclopedia
Sulfites (also sulphites) are compounds that contain the sulfite ion SO32- (IUPAC name sulfate(IV) ion).
Structure
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.
Commercial uses
Wine
Sulfites occur naturally in all wines to some extent. 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.
In the US, wine bottled after mid-1987 must have a label stating that they contain sulfites if they contain more than 10 parts per million.
In the EU an equivalent regulation came into force in November 2005. Organic wines are not necessarily sulfite-free.
Other food
Sulfites are often used as preservatives in dried fruits, and dried potato products.
Most beers no longer contain sulfites. Although shrimp is 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 which are usually eaten raw.
Health risks
Sulfites are used in increasing amounts as a food preservative or enhancer. They may come in various forms, such as:
Sulfites are considered one of the top 9 food allergens, but in reality the reaction to sulfite is not a true allergy. It may cause breathing difficulty within minutes after eating a food containing it, but more commonly causes headaches and skin irritation within a few hours after consumption. Asthmatics and possibly people with salicylate sensitivity (or aspirin sensitivity) are at an elevated risk for reaction to sulfites. The reaction can, but not often, be fatal, and the individual must immediately go to an emergency room. Other symptoms include sneezing, swelling of the throat, and hives. Barring simple overindulgence of alcohol, sulfites are the main reason why many people suffer headaches after drinking wine. In general, white and sweet (dessert) wines contain more sulfites than red wines. It is important for sensitive individuals to look for wines labeled "sulfite-free."
There are no labeling regulations that require products to indicate the presence of sulfites; however, many companies have added "contains sulfites" on product labels where applicable. Regulations do exist to require indication in the ingredients labels if sulfites were added to a product, but this requirement applies only if they were intentionally added in formulation and not if they are contained in an ingredient. If a product includes an ingredient that contains sulfites, such as dried fruit, then the ingredients label will list only "dried fruit" and is not required to indicate whether the dried fruit itself contains sulfites. Furthermore, the products most likely to contain sulfites (fruits and alcoholic beverages) do not require ingredients labels, so the presence of sulfites is usually undisclosed.
Sulfites are widely used to extend the shelf life of products. Because it is often difficult to know whether a food contains sulfites, many people do not realize that they may have a sensitivity to sulfite. Sulfites are also known to destroy vitamin B1 (thiamin), a vitamin essential for metabolism of carbohydrates and alcohol.
See also
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