Novel gases

Argon

Argon has the same properties as nitrogen. It is a chemically inert, tasteless, odourless gas that is heavier than nitrogen and does not affect micro organisms to any greater degree. It is claimed to inhibit enzymic activities, microbial growth and degradative chemical reactions (CCFRA R&D Report 125). Hence it can be used in a controlled atmosphere to replace nitrogen in most applications. Its solubility (twice that of nitrogen) and certain molecular characteristics give it special properties for use with vegetables. Under certain conditions, it slows down metabolic reactions and reduces respiration.

However, there is still a lack of conclusive evidence that the partial or total substitution of nitrogen with argon has commercially beneficial effects in terms of shelf-life extension and quality.

Work carried out by Air Products has shown that argon demonstrates some properties, which are beneficial to the MAP process; however, the argument for replacing nitrogen with argon is marginal, especially when the additional costs of the gas and associated piping are taken into account.

Carbon monoxide

Carbon monoxide is a toxic, colourless, odourless, flammable gas. It is stable at up to 400°C with respect to decomposition into carbon and oxygen.

Results have shown that the use of carbon monoxide (CO) in MAP with high levels of CO₂ has resulted in increased shelf-life together with retention of the bright red colour of meat cuts. It is also claimed that carbon monoxide can effectively reduce or inhibit different spoilage and pathogenic bacteria (Sorheim, Nissen, Aune and Nesbakken 2001)*.

The use of CO in MAP is allowed in certain countries, however, it is not on the European list of approved food additives, hence it cannot be used within the EC.

Ozone

Ozone gas is an unstable form of oxygen which has been noted for its oxidising and disinfecting properties and use in the preservation of food. It can only be delivered safely up to about 15% concentration in air or oxygen, having only a half life of 20min in clean water. One of its major benefits is that it will break down to harmless elemental oxygen. Because of its instability it is generated onsite from clean air or oxygen close to where it is required.

Ozone is most effective when in solution or in high humidity gas. Much of the early research was carried out on the disinfection of water, where it is shown to be much more effective than chlorine for a broad spectrum of microbial contaminants.

The application of ozone gas in MAP, to improve both shelf-life and safety, has been the focus of much research. But a successful offering is limited due to ozone’s non-specific oxidising capacity and short life. This means it is just as likely to attack the pack as the microbial contaminants, and any effect will be only for the first few minutes of the packs life. After this the ozone will have reacted, leaving a slightly higher oxygen content. Too much ozone can cause pack damage or discolouration, and may oxidise the surface of the product causing the release of nutrients which will encourage growth of the organisms you are trying to control.

In the USA where ozone is now an approved food additive, most of the products in the market use ozone dissolved in water for washing of equipment and produce to aid in microbial control. Full approval in the EU has not yet occurred.