What is Sodium Metabisulfite?
Sodium metabisulfite is a reducing agent used in dough. It is used frequently in cookie and cracker production.1 It is also used as a preservative for baked goods, wine, dried fruit and jams due to its antioxidant capacity.
Sodium metabisulfite can be produced by crystallizing a solution of sodium bisulfite.2 Sodium bisulfite results from introducing sulfur dioxide into a solution of sodium sulfite. Sodium sulfite, in turn, can be produced by introducing sulfur dioxide into sodium hydroxide.
As a reducing agent, sodium metabisulfite makes the dough flexible for better sheeting, and this is the rationale for sodium metabisulfite’s working as reducing agent. It reacts with the cysteine amino acids in dough, creating S-sulfocysteine residues within the protein structure, which inhibit the restoration of disulfide bonds.
Essentially, sodium metabisulfite acts as a cap, covering the reactive thiol group on cysteine, so it is unavailable to reform disulfide bonds.1 Lack of adequate disulfide bonds means that dough can’t form a strong gluten network.
Recent studies show that the presence of sodium metabisulfite slows down the Maillard reaction, thereby reducing levels of acrylamide.3
Compared with other reducing agents, like glutathione and L-cysteine, sodium metabisulfite has the greatest reducing capacity. There is far greater danger of over-dosing a formulation.1 The reducing power is one reason that sodium metabisulfite is not the preferred reducing agent in the industry. It is usually used at 0.03% dry flour weight in cracker production. It is rarely used in bread dough production.
Sodium metabisulfite is GRAS as a chemical preservative, regulated by the FDA in article 21CFR182.3766 of the Code of Federal Regulations.4
- Fort, E.L. “Effect of Reducing Agents on Batter Consistency and Physical Characteristics of Bread from Sorghum Flour.” Kansas State University Master Thesis, 2016, pp. 25–26.
- Zolotoochin, V.M., et al. “Patent US5976485 – Sodium Metabisulfite Process.” Google Patents, Google, 2 Nov. 1999, www.google.com/patents/US5976485. Accessed 8 Sept. 2017.
- Erbas, M., et al. “Effect of Sodium Metabisulfite Addition and Baking Temperature on Maillard Reaction in Bread.” Journal of Food Quality, vol. 35, no. 2, 2012, pp. 144–151, doi:10.1111/j.1745-4557.2012.00439.x.
- U.S. Food & Drug Administration. “21CFR182.3766 – Code of Federal Regulations Title 21.” Accessdata.fda.gov, 1 Apr. 2017, www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=182.3766. Accessed 8 Sept. 2017.