Sodium metabisulfite

Sodium metabisulfite

Sodium metabisulfite has found use as a reducing agent in the manufacture of biscuits, especially the low-fat, low-sugar types embraced by the generic term ‘semi-sweet’.

CAS number: 7681-57-4

E number: E223

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Description

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Sodium metabisulfite

CAS number: 7681-57-4

E number: E223

Sodium metabisulfite has found use as a reducing agent in the manufacture of biscuits, especially the low-fat, low-sugar types embraced by the generic term ‘semi-sweet’.

The level of gluten development occurring during the mixing of semi-sweet biscuit dough is considerably less than that achieved in bread dough mixing but with stronger flours it is still sufficient to contribute to biscuit shrinkage.

This shrinkage may be seen during the sheeting processes but is commonly seen when the biscuit units have been cut from the sheet. In severe cases the shrinkage is immediately after cutting while in less severe cases it may only be observed as shrinkage after the biscuit has been baked. In this case the biscuit dimensions will differ from those used in cutting and round biscuit shapes commonly develop eccentricity. The use of sodium metabisulphite is not universally accepted (Manley, 2000) and common ‘additive-free’ approaches are to more closely specify the qualities of the flour to be used or to add more water during dough mixing to yield a less elastic gluten network.

Preparation

Sodium metabisulfite can be prepared by evaporating a solution of sodium bisulfite saturated with sulfur dioxide:

2 HSO3− ⇌ H2O + S2O52−

which yields a residue of colorless solid Na2S2O5

Chemical properties

When mixed with water, sodium metabisulfite releases sulfur dioxide (SO2), a pungent, unpleasant smelling gas that can also cause breathing difficulties in some people. For this reason, sodium metabisulfite has fallen from common use in recent times, with agents such as hydrogen peroxide becoming more popular for effective and odorless sterilization of equipment. Released sulfur dioxide however makes the water a strong reducing agent.

Sodium metabisulfite releases sulfur dioxide in contact with strong acids:

Na2S2O5 + 2 HCl → 2 NaCl + H2O + 2 SO2

On heating to high temperature, it releases sulfur dioxide, leaving sodium sulfite behind:

Na2S2O5 → Na2SO3 + SO2

You may have seen the name before when browsing the ingredient list on the back of a bag of potato chips or raisins: sodium metabisulfite. But what you might not know is this common food preservative, with a mouthful of a name, has a number of other uses too.

What is Sodium Metabisulfite?

Sodium metabisulfite is an inorganic compound composed of sodium, sulfur and oxygen. It’s typically a white, or yellowish-white crystalline powder that easily dissolves in water, which leaves that unpleasantly familiar sulfur smell.

In Food

Sodium metabisulfite is commonly used as a food preservative for dried foods like potato chips, raisins and apples, as well as fruit concentrate juices. As a food product, the safe daily intake of sodium metabisulfite has been determined to be about .7 grams per kilogram of body weight. However, those with allergies to sulfites – often exhibited by rashes, hives and wheezing – may want to steer clear of this preservative altogether.

As a Cleaning Agent

The compound is also present in wines and beers, as it’s used as both a sterilizer and an antioxidant in the process of brewing beer or fermenting wine. If you or someone you know claims to have an allergy to red wine, it’s probably because of the presence of sodium metabisulfite.

As an antibacterial, the chemical is also used in the process of purifying water, cleaning water pipes and reverse osmosis membranes in desalinization equipment.

Additional Uses

Its acidic and preservative properties also make it an effective substitute for sodium bisulfite, a chemical that’s used in traditional darkroom photography. Also, sodium metabisulfite is used as a bleaching agent in pulp and textile manufacture, as well as a reducing agent in pharmaceuticals. It’s also a known preservative in cosmetics.

The chemical, in concentrated form, has also been used in landscape gardening as a tree stump remover, as it disintegrates the lignins – chemicals in plant cell walls – in the tree stumps, making them easier to remove.

Toxicity

While the allowable ingestion of sodium metabisulfite as a food preservative reduces it to sulfate in the liver, allowing for harmless elimination, excess exposure has been known to damage the immune system. It has also been linked to cancer, reproductive, developmental toxicity and neurotoxicity. Those with asthma and other allergies may also be sensitive to sodium metabisulfite.

Other Names

If you’re into checking the labels of your food, drinks or household cleaning agents, keep in mind that sodium metabisulfite goes by a number of other names too, including sodium pyrosulfite; disodium salt pyrosulfurous acid; disulfurous acid, disodium salt, pyrosulfurous acid, disodium salt; sodium disulfite; sodium pyrosulfite; sodium disulfite; disodium disulfite.

Sodium metabisulfite : Sodium metabisulfite has found use as a reducing agent in the manufacture of biscuits, especially the low-fat, low-sugar types embraced by the generic term ‘semi-sweet’.

CAS number: 7681-57-4

E number: E223

Product Specification :