People often ask me, what is the difference between an oxygen absorber and oxygen scavenger?

In respect to small devices that are added to food, and pharmaceutical products, oxygen absorbers, oxygen scavenger are the same thing, just different names for the same thing.

Oxygen scavengers or oxygen absorbers are added to packaging with food or pharmaceutical products, much like silica gel, and then enclosed to modify the atmosphere in the packaging (i.e. remove oxygen to leave nitrogen and carbon dioxide). This leads to improvement of product safety and shelf life extension. A extensive review has been written by Cichello 2015, with the ferrous type being most common, there are many other oxygen absorbers available to cover a wide array of applications and varying in absorption efficiency and speed.

The components of an oxygen absorber vary according to intended use, but typically contain a hydrated metal carbonate i.e. iron II carbonate or calcium carbonate, with a desiccant such as activated carbon [water adsorption sites], salt as a catalyst and some moisture. The oxygen absorber or scavenger, like silica gel desiccant is enclosed in a porous sachet or packet typically paper or polyethylene combination but can also be embedded into packaging films and structures or polymer structure. There are some innovative patents that propose the re-use as a soil fertiliser/ conditioner.

The first patent for an oxygen scavenger used an alkaline solution of pyrogallic acid in an air-tight vessel, but also the use of asorbic acid by the British military in food rations in the 1930's.

When an oxygen absorber is removed from the master packaging with low oxygen transmission rate, the atmospheric moisture begins to become adsorbed onto the activated carbon and interact with the iron particles inside of the absorber sachet and oxidizes to form iron oxide (i.e. 65% relative humidity); see figure 1 below, with salt acting as a catalyst at lower humidities, as a result oxygen level in the surrounding atmosphere will fall below 0.01% with 1 g of iron adsorbing 300 mL of oxygen. Non-ferrous oxygen absorbers/ scavengers exist but due to the price of other metals and also ascobic acid, ferrous or calcium carbonate are generally used. Other substitution for ferrous carbonate, Zinc, Manganese, Boron etc, but iron is the cheapest metal that can oxidize and thus the most used. Other non metal compounds include ascorbic acid can be used. A good introduction can be found here. A comprehensive review by Cichello 2015 can be found here. Also a useful Facebook page; Oxygen Absorber Australia.

There size of oxygen absorbing capacity can range from 20cc, the smallest, to 50cc, 100cc, 200cc, 300cc, 400cc, 500cc, 1000cc, and 2000cc being one of the largest.

The activated carbon absorbs moisture, and the salt acts as a catalyst to activate the oxidation of the ferrous carbonate to ferric oxide. Due to residual moisture added, oxygen absorbers are self acting and commence absorption as soon as the oxygen absorber packets are exposed to oxygen (i.e. bag is opened).

The benefits of oxygen scavengers include;
- The removal of oxygen, leading to less oxidation of flavour compounds in foods i.e. retain fresh-roasted flavor of coffee and nuts, prevents the oxidation of spice oleoresins present in spices themselves and in seasoned foods.
- Prevents oxidation of vitamins A, C and E, extends life of pharmaceuticals
- Inhibits mould growth in breads, beef jerky, cheeses, reducing non-enzymatic browing of fruit and vegetables,
- Killing insects and weevils in a museum/ art gallery environment (oxygen deprivation)
- Oxygen scavenging technology can quickly reduce oxygen levels in sealed containers to below 0.01%.

4Fe + 3O2 + 6H2O ---> 4Fe(OH)3

Figure 1. Chemical reaction of ferrous based oxygen absorber (rusting process)

Moreover, OxySorb oxygen absorbers are packed with an oxygen indicator.
The indicator maybe comprised of methylthionine chloride (<1%) (methylene blue) [non-toxic], and Rhodamine dye (<1%); which changes from a pink colour to blue colour when exposed to oxygen and atmospheric moisture.

Typically foods with an available water content of less that 0.6 may not need an oxygen absorber if hermetically sealed and the oxygen transmission rate of the container is <1cc/m^2/24hr period at ambient conditions.

To calculate the correct sized oxygen absorber to use, you need to contact a technical specialist as there are at least if not more than 10 factors that could impact oxygen in the product and thus shelf-life of the product.

Contrary to popular belief, OxySorb oxygen absorbers can actually be re-used as a soil fertilizer. See patent below for description, this is the only one in existence globally and registered by Wholesale Group International Pty. Ltd. [IP Australia Patent Number; 2017101028]

Summary:

Oxygen absorber absorb oxygen. They can be in a powdered form added to film, or food i.e. ascorbic acid (vitamin C) (Dave et. al. 1997). They are sometimes also called 'Oxygen Scavengers', 'oxygen absorber packets', 'o2 absorbers', 'oxygen packs', 'oxygen removers'. Primarily, oxygen absorbers are used for food storage i.e. fresh fruit and vegetables (Charles et. al. 2003), walnuts (Jensen et. al. 2003), raw almond kernels (Mexis & Kontominas 2010) & fruit colour stabilizer (Tarr & Clingeleffer 2005), with CO2 aborbers in strawberries (Aday et. al. 2011; Kartel et. al. 2012) but also for use with pharmaceutical products and also equipment storage as well. Extensive literature reviews regarding oxygen absorbers and active packaging have been written by Miltz & Perry 2004, Han 2005, Rooney 2005, Kadoya 2012, Tian et. al. 2013, Realini & Marcos 2014 & Cichello 2015. They can be placed in high oxygen barrier containers i.e. HDPE tubs or packaging i.e. PVdC coated PET/ or Nylon. A popular choice is mylar bags which are commonly used in food storage. Mylar food storage bags are used by the military but also those preparing for food shortage which is a normal occurance in nature and also human civilisation due to war, faminie and pestilance.

Some common brands include OxySorb (Wholesale Group International), Ageless (Mitsubishi), which are food grade oxygen absorbers; HACCP and USFDA compliant and so forth. Often, oxygen absorbers are used in combination with moisture absorbing packets such as silica gel or silica/ clay gel desiccants. They are not 'deoxidizers'. They can be combined with ethanol emitters (Latou et. al. 2010) in sliced wheat bread preservation, gluten free bread (Gutiérrez et. al. 2011), combined witrh rosemary oil extract in rainbow trout fillets (Mexis et. al. 2009), Greek cod paste (Mexis et. al. 2009), catfish steaks (Mohan et. al. 2006), chicken meat and citrus extract (Mexis et. al. 2012)and modified atmosphere packing with pork sausages