Since external influences such as oxygen, humidity, light, temperature or microorganisms are the main factors leading to undesirable changes in food products, the atmosphere in which each product is packaged plays a crucial role in terms of its subsequent shelf life. However, the shelf life of each product is not just influenced by external factors but also by the structure of the product itself, such as any sensitive ingredients it may contain. Modified atmosphere packaging has therefore long been an integral part of the food industry. However, not only does this method extend the shelf life of products many times over, it also dispenses with pressure, such as occurs for example in vacuum packaging. So, among other things MAP prevents the products from drying out. This is the only way to ensure optimal long-term preservation of the food’s quality, appearance and taste.

That is why food packaging under protective gases (Modified Atmosphere Packaging, or MAP for short) has established itself as one of the most effective methods of extending the shelf life of foodstuffs. The process involves specifically altering the ambient atmosphere during packaging by means of protective gases.

Messer offers a range of food grade gases for modified atmosphere packaging of food products. The company’s Gourmet brand includes carbon dioxide, nitrogen, oxygen and argon – all of which occur naturally in the atmosphere. Nitrogen (Gourmet N) – an inert, reaction-inhibiting gas – displaces oxygen and thereby prevents oxidation. However, due to its low solubility in food, nitrogen is also used as a supporting gas to prevent the packaging from collapsing. At 78.08 per cent by volume, it is the main component of air. Argon (Gourmet A) is another inert gas that is used as a displacement and supporting gas. In addition, it inhibits enzymatic activities and increases the bacteriostatic effect of carbon dioxide. CO₂ – carbon dioxide (Gourmet C) – is colourless, tasteless and odourless. It is also highly soluble in liquid and fatty phases of foodstuffs. The associated decrease in the pH value has a bacteriostatic effect and reduces the growth of bacteria and mould. Oxygen (Gourmet O) – making up 20.95 per cent of ambient air by volume – is only used in specific cases in modified atmosphere packaging, for instance to preserve the red colour of meat or inhibit anaerobic bacteria. However, oxygen is also important for respiration when packaging plant-based food products such as fruit and vegetables. The gas mixtures are always tailored to the specific product and comply with all the laws and standards governing food products, for instance concerning purity or traceability. In most cases, the mixtures consist of at least two of Messer’s Gourmet gases. They are either supplied as ready-made standard mixtures in cylinders or mixed individually on site at the customer location.

The different types of packaging
In the food industry, packaging has a number of important functions to fulfil. It is supposed to protect the preserved product from the environment and prevent mechanical damage while at the same time satisfying all the marketing strategy and visual requirements and being commercially viable. Particularly with fresh products, the packaging must not only prevent contamination by germs but also ensure that the desired environmental conditions inside the packaging are preserved over an extended period. For this reason, the packaging material itself also plays a key role in food preservation. Ideally, it should be impervious to microorganisms, gases, water, steam, aromas and light – an exception being fruit and vegetable packaging, where a certain degree of exchange with the ambient air is desirable in order to support controlled plant respiration (EMAP – Equilibrium Modified Atmosphere).

Apart from the product type (solid, pasty, liquid), factors such as the shelf life requirements, costs, marketing strategy and ecofriendliness also determine which packaging materials are used in each particular case. The most common types of packaging include tins, plastic film packaging, composite cans, jars, preformed plastic containers, thermoformed packs, tubular bag packaging and side-sealed bag packaging. Tins are completely sealed, impervious to light and dimensionally stable – the drawback, however, is that the product itself is not visible, unlike with jars or plastic film packaging. The latter is available in wide-ranging levels of quality.

Shelf life extension
The highest levels of hygiene are always an absolute must, no matter what kind of packaging and which method of shelf life extension is used. The most effective methods include cooling, freezing, heat sterilisation, lowering of the pH value through chemical additives or the addition of carbon dioxide, as well as natural acidification by means of lactic acid fermentation. These shelf-life-extending measures have one thing in common: they already represent an initial phase of preparation. The situation is different when it comes to modifying the atmosphere or pressure inside the packaging through the use of Messer Gourmet gases – this process involves little or no change in the freshness characteristics of the food products. Further methods of shelf life extension include drying and vacuum packaging.

Shelf life of beverages
Beverages, too, must be produced with the longest possible shelf and storage life. CO₂ is also used for carbonation and impregnation in the beverage sector due to its high degree of solubility in liquids as well as its capacity to restrict – or inhibit altogether – the growth of harmful microorganisms. This not only produces the sparkling carbon dioxide bubbles that lend the beverage its refreshing quality; it also displaces atmospheric oxygen from the container, allowing oxidation reactions to be significantly reduced. Beverages mixed with CO₂ thus have a longer shelf life and retain their flavour throughout the entire production process as well as during storage and transportation. Messer supplies the necessary quantity of carbon dioxide for carbonation in liquid as well as gaseous form: in storage vessels, steel cylinders or bundles.

In the case of non-carbonated beverages such as still mineral water or fruit juices to be bottled or canned in thin-walled PET bottles or cans, the cryogenic injector is used. This involves liquid nitrogen being injected onto the surface of the liquid immediately before the beverage container is sealed, after which it evaporates in the sealed container. In this way, it displaces the oxygen from the headspace of the bottles or cans, thereby extending the product’s shelf life. Thanks to the increased internal pressure that is produced as a result of the cryogenic injection process, the containers themselves remain stackable even after extended periods of storage and transportation.

Nitrogen has the added advantage that it allows the use of very thin-walled containers, which in turn leads to substantial savings on the cost of materials. Over and above that, it changes neither the flavour nor the character of the beverage.

Gas supply systems
The right gas supply system also plays an extremely important role in modified atmosphere packaging – not just in terms of a seamless and reliable supply, but also with regard to cost efficiency. Besides selecting the optimal gas, it is also necessary, of course, to choose the appropriate hardware such as valves, pressure regulators, withdrawal points, expansion stations and accessories. And, of course, there are also regulations that have to be complied with. In this regard, Messer offers everything from a single source – from technical know-how and comprehensive expert consultancy to all the necessary components and complete automation of the gas supply. Messer’s portfolio of protective gases includes its own Gourmet gases as well as all the usual commercially available gases of the highest standards of quality, along with custom gas mixtures.