Sodium nitrite is an inorganic compound with the chemical formula NaNO2. It is a white to slightly yellowish crystalline powder that is very soluble in water and is hygroscopic. From an industrial perspective, it is the most important nitrite salt. It is a precursor to a variety of organic compounds, such as pharmaceuticals, dyes, and pesticides, but it is probably best known as a food additive used in processed meats and (in some countries) in fish products.
Uses
Industrial chemistry The main use of sodium nitrite is for the industrial production of organonitrogen compounds. It is a reagent for conversion of amines into diazo compounds, which are key precursors to many dyes, such as diazo dyes. Nitroso compounds are produced from nitrites. These are used in the rubber industry. It is used in a variety of metallurgical applications, for phosphatizing and detinning. Sodium nitrite is an effective corrosion inhibitor and is used as an additive in industrial greases, as an aqueous solution in closed loop cooling systems, and in a molten state as a heat transfer medium.
Food additive and preservative Sodium nitrite is used to speed up the curing of meat, inhibit the germination of Clostridium botulinum spores, and also impart an attractive pink color. Nitrite reacts with the meat myoglobin to cause color changes, first converting to nitrosomyoglobin (bright red), then, on heating, to nitrosohemochrome (a pink pigment). Historically, salt has been used for the preservation of meat. The salt-preserved meat product was usually brownish-gray in color. When sodium nitrite is added with the salt, the meat develops a red, then pink color, which is associated with cured meats such as ham, bacon, hot dogs, and bologna. In the early 1900s, irregular curing was commonplace. This led to further research surrounding the use of sodium nitrite as an additive in food, standardizing the amount present in foods to minimize the amount needed while maximizing its food additive role. Through this research, sodium nitrite has been found to give taste and color to the meat and inhibit lipid oxidation that leads to rancidity, with varying degrees of effectiveness for controlling growth of disease-causing microorganisms. The ability of sodium nitrite to address the above-mentioned issues has led to production of meat with extended storage life and has improved desirable color and taste. According to scientists working for the meat industry, nitrite has improved food safety. This view is disputed in the light of the possible carcinogenic effects caused by adding nitrites to meat. Nitrite has the E number E250. Potassium nitrite (E249) is used in the same way. It is approved for usage in the European Union, United States, and Australia and New Zealand. In meat processing, sodium nitrite is never used in a pure state but always mixed with common salt. This mixture is known as nitrited salt, curing salt or nitrited curing salt. In Europe, nitrited curing salt contains between 99.1% and 99.5% common salt and between 0.5% and 0.9% nitrite. In the US, nitrited curing salt is dosed at 6.25% and must be remixed with salt before use.
Color and taste The appearance and taste of meat is an important component of consumer acceptance. Sodium nitrite is responsible for the desirable red color (or shaded pink) of meat. Very little nitrite is needed to induce this change. It has been reported that as little as 2 to 14 parts per million (ppm) is needed to induce this desirable color change. However, to extend the lifespan of this color change, significantly higher levels are needed. The mechanism responsible for this color change is the formation of nitrosylating agents by nitrite, which has the ability to transfer nitric oxide that subsequently reacts with myoglobin to produce the cured meat color. The unique taste associated with cured meat is also affected by the addition of sodium nitrite. However, the mechanism underlying this change in taste is still not fully understood.
Inhibition of microbial pathogens In conjunction with salt and pH levels, sodium nitrite reduces the ability of Clostridium botulinum spores to grow to the point of producing toxin. Some dry-cured meat products are manufactured without nitrites. For example, Parma ham, which has been produced without nitrite since 1993, was reported in 2018 to have caused no cases of botulism. This is because the interior of the muscle is sterile and the surface is exposed to oxygen. Other manufacture processes do not assure these conditions, and reduction of nitrite results in toxin production. Sodium nitrite has shown varying degrees of effectiveness for controlling growth of other spoilage or disease causing microorganisms. Although the inhibitory mechanisms are not well known, its effectiveness depends on several factors including residual nitrite level, pH, salt concentration, reductants present and iron content. The type of bacteria also affects sodium nitrite's effectiveness. It is generally agreed that sodium nitrite is not effective for controlling Gram-negative enteric pathogens such as Salmonella and Escherichia coli. Other food additives (such as lactate and sorbate) provide similar protection against bacteria, but do not provide the desired pink color.
Inhibition of lipid peroxidation Sodium nitrite is also able to effectively delay the development of oxidative rancidity. Lipid peroxidation is considered to be a major reason for the deterioration of quality of meat products (rancidity and unappetizing flavors). Sodium nitrite acts as an antioxidant in a mechanism similar to the one responsible for the coloring effect. Nitrite reacts with heme proteins and metal ions, neutralizing free radicals by nitric oxide (one of its byproducts). Neutralization of these free radicals terminates the cycle of lipid oxidation that leads to rancidity.
Medication
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