Science and technology of modified atmosphere packaging
Written by Michael Mullan
This section contains summary information on modified atmosphere packaging. More comprehensive treatment is available in a chapter on modified atmosphere packaging, written by the author and Derek McDowell, in the book Food Packaging Technology. Derek McDowell is Head of Supply and Packaging at Loughry Campus and is a packaging specialist.
This book, edited by Cole, Kirwan and McDowell, was published by Blackwell Publishing in August, 2003. The author's chapter deals with the food science and technology of food packaging including packaging materials, their properties, selection for packaging applications, and packaging equipment. The chapter has been updated and a second edition of the book was published in 2012. As a result of this revision, the list of references previously available for downloading has been extensively updated and the original downloadable list has been removed (January, 2010). An updated list is now available.
Many foods spoil rapidly in air due to moisture loss or uptake, reaction with oxygen and the growth of aerobic micro-organisms i.e., bacteria and moulds. Microbial growth results in changes in texture, colour, flavour and nutritional value of the food. These changes can render food unpalatable and potentially unsafe for human consumption. Storage of foods in a modified gaseous atmosphere can maintain quality and extend product shelf life by slowing chemical and biochemical deteriorative reactions and by slowing or in some instances preventing the growth of spoilage organisms.
Modified atmosphere packaging (MAP) is defined as "the packaging of a perishable product in an atmosphere which has been modified so that its composition is other than that of air" (Hintlian and Hotchkiss, 1986). Whereas controlled atmosphere storage involves maintaining a fixed concentration of gases surrounding the product by careful monitoring and addition of gases, the gaseous composition of fresh MAP foods is constantly changing due to chemical reactions and microbial activity. Gas exchange between the pack headspace and the external environment may also occur because of permeation across the package material.
Packing foods in a modified atmosphere can offer extended shelf life and improved product presentation in a convenient container, making the product more attractive to the retail customer. However, MAP cannot improve the quality of a poor quality food product. It is therefore essential that the food be of the highest quality prior to packing in order to optimise the benefits of modifying the pack atmosphere.
Good hygiene practice and temperature control throughout the chill-chain for perishable products are required to maintain the quality benefits and extended shelf life of MAP foods.
Gases used in modified atmosphere packaging
The three main gases used in modified atmosphere packaging are O2, CO2 and N2. The choice of gas is very dependent upon the food product being packed. Used singly or in combination, these gases are commonly used to balance safe shelf life extension with optimal organoleptic properties of the food. Noble or 'inert' gases such as argon are in commercial use for products such as coffee and snack products; however, the literature on their application and benefits is limited. Experimental use of carbon monoxide (CO) and sulphur dioxide (SO2) has also been reported.
• Carbon dioxide
Carbon dioxide is a colourless gas with a slight pungent odour at very high concentrations. It is an asphyxiant and slightly corrosive in the presence of moisture. CO2 dissolves readily in water (1.57 g/kg @ at 100 kPa, 20° C) to produce carbonic acid (H2CO3) that increases the acidity of the solution and reduces the pH. This gas is also soluble in lipids and some other organic compounds. The solubility of CO2 increases with decreasing temperature. For this reason, the antimicrobial activity of CO2 is markedly greater at temperatures below 10° C than at 15° C or higher. This has significant implications for MAP of foods. The high solubility of CO2 can result in pack collapse due the reduction of headspace volume. In some MAP applications, pack collapse is favoured, for example in flow wrapped cheese for retail sale.
Oxygen is a colourless, odourless gas that is highly reactive and supports combustion. It has a low solubility in water (0.040 g/kg at 100 kPa, 20° C). Oxygen promotes several types of deteriorative reactions in foods including fat oxidation, browning reactions and pigment oxidation. Most of the common spoilage bacteria and fungi require oxygen for growth. Therefore, to increase shelf life of foods the pack atmosphere should contain a low concentration of residual oxygen. It should be noted that in some foods a low concentrations of oxygen can result in quality and safety problems (for example unfavourable colour changes in red meat pigments, senescence in fruit and vegetables, growth of food poisoning bacteria) and this must be taken into account when selecting the gaseous composition for a packaged food.
Nitrogen is a relatively un-reactive gas with no odour, taste, or colour. It has a lower density than air, non-flammable and has a low solubility in water (0.018 g/kg at 100 kPa, 20° C) and other food constituents. Nitrogen does not support the growth of aerobic microbes and therefore inhibits the growth aerobic spoilage but does not prevent the growth of anaerobic bacteria. The low solubility of nitrogen in foods can be used to prevent pack collapse by including sufficient N2 in the gas mix to balance the volume decrease due to CO2 going into solution.
• Carbon Monoxide
Carbon monoxide is a colourless, tasteless and odourless gas that is highly reactive and very flammable. It has a low solubility in water but is relatively soluble in some organic solvents. CO has been studied in the MAP of meat and has been licensed for use in the USA to prevent browning in packed lettuce. Commercial application has been limited because of its toxicity and the formation of potentially explosive mixtures with air.
• Noble gases
The noble gases are a family of elements characterised by their lack of reactivity and include helium (He), argon (Ar), xenon (Xe) and neon (Ne). They, in particular argon, are sometimes used in MAP e.g. in potato-based snack products.
How to cite this article
Mullan, W.M.A. (2002) .
[On-line]. Available from: https://www.dairyscience.info/index.php/packaging/117-modified-atmosphere-packaging.html . Accessed: 8 July, 2020.
Modified January 2011.