Oxygen scavengers or oxygen absorbers are added to enclosed

packaging Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a c ...

to help remove or decrease the level of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

in the package. They are used to help maintain product safety and extend

shelf life Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a ...

. There are many types of oxygen absorbers available to cover a wide array of applications. The components of an oxygen absorber vary according to intended use, the water activity of the product being preserved, and other factors. Often the oxygen absorber or scavenger is enclosed in a porous

sachet A sachet is a small scented cloth bag filled with herbs, potpourri, or aromatic ingredients.Oster, p. 54 A sachet is also a small porous bag or packet containing a material intended to interact with its atmosphere; for example, desiccants ...

or packet but it can also be part of packaging films and structures. Others are part of a polymer structure.

Mechanism

The first patent for an oxygen scavenger used an alkaline solution of

pyrogallic acid Pyrogallol is an organic compound with the formula C6H3(OH)3. It is a water-soluble, white solid although samples are typically brownish because of its sensitivity toward oxygen. It is one of three isomers of benzenetriols. Production and reac ...

in an air-tight vessel. Modern scavenger

s use a mixture of iron powder and

sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35. ...

. Often

activated carbon Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area availa ...

is also included as it

adsorb Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...

s some other gases and many organic molecules, further preserving products and removing odors. When an oxygen absorber is removed from its protective packaging, the moisture in the surrounding atmosphere begins to permeate into the iron particles inside of the absorber

. Moisture activates the iron, and it oxidizes to form

iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of wh ...

. Typically, there must be at least 65% relative humidity in the surrounding atmosphere before the rusting process can begin. To assist in the process of oxidation, sodium chloride is added to the mixture, acting as a catalyst or activator, causing the iron powder to be able to oxidize even with relatively low humidity. As oxygen is consumed to form iron oxide the level of oxygen in the surrounding atmosphere is reduced. Absorber technology of this type may reduce the oxygen level in the surrounding atmosphere to below 0.01%. Complete oxidation of 1 g of iron can remove 300 cm³ of oxygen in standard conditions. Though other technologies can remove more, iron is the most useful as it does not cause odor like sulfur compounds or passivate like aluminium compounds. Many other alternatives are not food safe. The moisture requirement of iron-based scavengers makes them ineffective in moisture sensitive applications. The performance of oxygen scavengers is affected by ambient temperature and relative humidity. Newer packaging technologies may use oxygen scavenging polymers to prevent accidental ingestion of oxygen scavengers.

Non-ferrous oxygen scavengers

While most standard oxygen scavengers contain ferrous carbonate and a metal

halide In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a flu ...

catalyst, there are several non-ferrous variants, such as

ascorbate Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) and ...

with

sodium hydrogen carbonate Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3−) ...

, among others available. Typical reasons to use a non-ferrous variant would include the packaging of products intended for international shipping where metal detection would pose a problem; a desire to reduce the odor associated with ferrous carbonate; or dietary products where contact with iron should be avoided.

Ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) ...

is often used to scavenge oxygen for generation of anaerobic environments for

microbiology Microbiology () is the scientific study of microorganisms, those being unicellular (single cell), multicellular (cell colony), or acellular (lacking cells). Microbiology encompasses numerous sub-disciplines including virology, bacteriology, ...

Benefits of oxygen scavengers

* Helps retain fresh-roasted flavor of coffee and nuts * Prevents oxidation of spice

oleoresin Oleoresins are semi-solid extracts composed of resin and essential or fatty oil, obtained by evaporation of the solvents used for their production. The oleoresin of conifers is known as crude turpentine or gum turpentine, which consists of oil of ...

s present in spices themselves and in seasoned foods * Prevents oxidation of vitamins A, C and E * Extends life of

pharmaceuticals A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and re ...

* Inhibits mold in natural cheeses and other fermented dairy products * Delays non-enzymatic browning of fruits and some vegetables * Inhibits oxidation and condensation of red pigment of most berries and sauces * Oxygen deprivation contributes to a pest-free environment in museums Oxygen scavenging technology can quickly reduce oxygen levels in sealed containers to below 0.01%.

Typical uses

* Pharmaceuticals and vitamins * Medical diagnostic kits and devices * Potassium Metabisulfite is often used in the wine industry to both scavenge oxygen and provide a layer of gas that separates wine from oxygen. * Foods prone to

rancidification Rancidification is the process of complete or incomplete autoxidation or hydrolysis of fats and oils when exposed to air, light, moisture, or bacterial action, producing short-chain aldehydes, ketones and free fatty acids. When these processes o ...

, including: :* Nuts and snacks :* Whole fat dry foods :* Processed, smoked and cured meats (including jerky and dried meat nuggets) :* Cheeses and dairy products :* Spices and seasonings :* Flour and grain items * Other foods, including :* Fresh and precooked pasta and noodles :* Birdseed and pet food :* Breads, cookies, cakes, pastries :* Candies and confectioneries :* Coffee and tea :* Dried fruits and vegetables * Artwork preservation * Preserving solderability of electronic parts

Sachets

Plastic sachets offer greater protection than paper as they are not prone to disintegrating in products with high fat contents.

References