- Structure
- Nomenclature
- Properties
- Physical state
- Molecular weight
- Melting point
- Specific weight
- Solubility
- pH
- Chemical properties
- Obtaining
- Uses in food
- As a preservative
- In the wine and other beverage industry
- To treat some flours, cereals and starches
- Foods that should not be used
- Other uses
- Risks
- References
The sodium metabisulfite is an inorganic compound consisting of two sodium ions Na + and metabisulfite or bisulfite ion S 2 O 5 2-. Its chemical formula is Na 2 S 2 O 5. It is a white crystalline solid. It is used as an antioxidant and antimicrobial agent in a variety of pharmaceuticals and functions as a preservative in many food preparations.
Na 2 S 2 O 5 is used to treat the flour to make cookies and confectionery sweets as it helps to break down protein molecules and make the dough easier to shape and does not shrink when cut into smaller pieces.
Solid Na 2 S 2 O 5 sodium metabisulfite. No machine-readable author provided. Walkerma assumed (based on copyright claims).. Source: Wikimedia Commons.
It is used in many processed foods to prevent them from being attacked by fungi and bacteria. These foods include cheeses, fruit juices, sauces, margarines, etc.
However, since some negative effects on human health have been noted, the maximum amount of sodium metabisulfite Na 2 S 2 O 5 that these foods should contain is controlled by licensed bodies.
The other applications of Na 2 S 2 O 5 are generally based on its reducing properties (the opposite of oxidant), such as to reduce the amount of chlorine in treated water, as wool bleach, in cosmetic formulas, among others. applications.
Structure
Sodium metabisulfite is made up of two Na + sodium ions and one S 2 O 5 2- bisulfite ion. The latter has two sulfur atoms attached to each other and five oxygen atoms distributed between them.
Chemical structure of sodium metabisulfite Na 2 S 2 O 5. Author: Benjah-bmm27. Source: Wikimedia Commons.
Nomenclature
-Sodium metabisulfite
-Sodium pyrosulfite
-Sodium disulfite
-Disodium disulfite
Properties
Physical state
Colorless, white or yellowish crystalline solid. Hexagonal crystals.
Molecular weight
190.11 g / mol
Melting point
At temperatures above 150 ° C it decomposes.
Specific weight
1.4 at 25 ° C / 4 ° C
Solubility
Very soluble in water: 66.7 g / 100 g of water.
pH
Its aqueous solutions are acidic. A 10% solution has a pH of 4.0-5.5.
Chemical properties
When dissolved in water, it becomes a corrosive acid. It has reducing and antioxidant properties.
If exposed to air, it slowly oxidizes to sodium sulfate Na 2 SO 4, also losing part of its SO 2 content.
Reacts with water to give sodium bisulfite NaHSO 3, sulfur dioxide SO 2 and sodium sulfite Na 2 SO 3.
It has a slight smell of sulfur. It is not combustible, but when subjected to heat it can generate toxic gases.
Obtaining
Sodium metabisulfite can be obtained by passing an excess of the sulfur dioxide gas SO 2 through a solution of sodium carbonate Na 2 CO 3.
Uses in food
As a preservative
Na 2 S 2 O 5 is an antioxidant. It serves as a preservative and inhibitor of certain microorganisms. Its antimicrobial effect is optimal below pH = 4, as in fruit juices.
It helps prevent spoilage and slow the blackening of certain foods. It has been used for example to prevent browning of sweet potatoes.
It is used during the harvest of marine shrimp to prevent the formation of black spots. Shrimp are dipped in a metabisulfite solution on ice.
Shrimp are sometimes dipped in aqueous sodium metabisulfite solution to prevent spoilage. Author: Aakashkhatu1998. Source: Pixabay.
It is an effective antioxidant and improves the retention of ascorbic acid (vitamin C) in dried fruits and juices. In these it inhibits certain types of bacteria, fungi and yeasts.
It has been used in South Africa to control spoilage and inhibit the browning of lychee fruit. However, it seems that the flavor of said fruit changes slightly.
Other foods in which it is used are cheese, various drinks, margarine, sauces, sweets and fish.
In the wine and other beverage industry
In grapes after harvest it is used as a fungicide, since certain fungi can grow on this fruit. It then acts on certain specific microorganisms, which makes it useful in the wine industry as it allows controlling its fermentation.
Residual metabisulfite is effective after wine fermentation to prevent the growth of alcohol tolerant yeasts.
It has also been used in apple juice and cider to control certain pathogenic microorganisms such as Escherichia coli.
To treat some flours, cereals and starches
It is used to condition the dough of some baked goods. It acts as a reducing agent in the manufacture of cookies, especially those low in fat and low in sugar, and in pastry sweets.
Metabisulfite reacts with the S – S sulfur bonds of the proteins contained in the flour of the dough with which cookies and sweets are prepared, softening it, making it more extensible and less elastic.
One of the goals is to prevent the dough from shrinking, either before or during baking. However, its use in cookie dough is not always accepted and other alternatives are preferred.
Some cheeses, jams, and crackers may contain sodium metabisulfite as a preservative. Author: Steve Buissinne. Source: Pixabay.
It is also used to bleach edible starches and to soften the corn kernels during the wet milling process.
Foods that should not be used
The US Food and Drug Administration, or FDA, has labeled sodium metabisulfite Na 2 S 2 O 5 as "generally considered safe."
However, it has been recognized by said body as an antithiamine or antivitamin B1 compound.
Therefore it should not be used in meats, or in foods that are a source of vitamin B1. Nor should it be used on fruits or vegetables that are sold raw to consumers or that are presented as fresh.
According to some consulted sources, if it is used in concentrations higher than 10 mg / Kg of food, it must be reported on the label of this.
Other uses
Other applications of Na 2 S 2 O 5 are shown below.
-As a reducing agent in cosmetic formulas and as an antioxidant, for example in hair care products.
-As an antioxidant in pharmaceutical preparations, such as syrups or injectable fluids. It is used in acid preparations. It has some antimicrobial activity, especially at acid pH.
-As a laboratory reagent, for example to preserve histamine when your analysis is performed.
Some liquid medicines may contain Na 2 S 2 O 5 as a preservative. Author: Steve Buissinne. Source: Pixabay.
-As a reducing agent in the development of photographs.
-To reduce chlorine in water from industrial processes and in wastewater treatment.
-In the textile industry: as a wool bleach, as an antichloro agent after nylon bleaching, to reduce some dyes and to solubilize others.
-To produce sulfur dioxide SO 2 at the site of use. For example, in silos of fresh grass, the SO 2 produced by sodium metabisulfite develops acidity quickly and allows the conservation of the material, since fermentation would take too long.
Wool can be bleached with sodium metabisulfite. Author: JacLou DL. Source: Pixabay.
Risks
-If the solid Na 2 S 2 O 5 is inhaled, it is toxic. Direct contact strongly irritates the skin, mucous membranes, and tissues. It is irritating to the eyes and respiratory system.
-If ingested directly, it can cause abdominal pain, diarrhea, nausea and vomiting.
-It is corrosive.
-Some asthmatics are said to be dangerously sensitive to minute amounts of metabisulfite in food.
-It is harmful to aquatic organisms.
References
- Cauvain, SP (2017). Raw materials. In Baking Problems Solved (Second Edition). Recovered from sciencedirect.com.
- US National Library of Medicine. (2019). Sodium metabisulfite. National Center for Biotechnology Information. Recovered from pubchem.ncbi.nlm.nih.gov.
- Sivakumar, D. and Korsten, L. (2011). Litchi (Litchi chinensis Sonn.). In Postharvest Biology and Technology of Tropical and Subtropical Fruits: Cocona to Mango. Recovered from sciencedirect.com.
- Danyluk, MD et al. (2012). Microbial decontamination of juices. In Microbial Decontamination in the Food Industry. Recovered from sciencedirect.com.
- Wieser, H. (2012). The use of redox agents in breadmaking. In Breadmaking (Second Edition). Recovered from sciencedirect.com.
- Ercan, S. et al. (2015). Induction of omega 6 inflammatory pathway by sodium metabisulfite in rat liver and its attenuation by ghrelin. Lipids in Health and Disease (2015) 14: 7. Recovered from ncbi.nlm.nih.gov.