The food industry is moving away from preservative methods that physically or chemically alter foodstuffs in favour of gentler techniques that protect the inherent quality of the food and leave the product unchanged. These alternative approaches range from high-pressure and microwave processes to packaging techniques such as oxygen absorption, vacuum, sous-videtechniques and modified atmosphere packaging (MAP).
MAP is a natural, shelf-life-enhancing method that is rapidly growing in popularity on an international scale. It often complements other methods. The correct MAP gas mixture maintains the quality of the foodstuff by retaining the original taste, texture and appearance.
The gas atmosphere must be carefully adapted to the individual foodstuff and its properties. In the case of low-fat products with high moisture content, MAP focuses on inhibiting the growth of micro organisms. Oxidation protection is the primary objective, however, in the case of products with a high fat content and low water activity.
MAP gas mixtures usually consist of the normal atmospheric gases: carbon dioxide, nitrogen and oxygen. Micro-organism growth can also be inhibited to a certain extent with the help of other gases such as nitrous oxide, argon and hydrogen. Each of the gases has its own unique properties that affect its interaction with the foodstuffs. The gases can be applied individually or mixed according to specific ratios.
Impressive results with carbon dioxide
Carbon dioxide is the most important gas in the field of MAP technology. Most micro organisms (such as mould and the most common aerobic bacteria) are strongly affected by carbon dioxide.
Carbon dioxide has a more limited impact on the growth of anaerobic micro-organisms. Carbon dioxide inhibits microbial activity by effectively dissolving into the food’s liquid and fat phase, thereby reducing its pH value. It also penetrates biological membranes, causing changes in permeability and function.
Nitrogen – inert and stabilising
Nitrogen is an inert gas. It is primarily used to replace oxygen in packaging, thereby preventing oxidation. Owing to its low solubility in water, nitrogen also helps to prevent package collapse by maintaining internal volume.
Oxygen level should be as low as possible
For most foodstuffs, the package should contain as little oxygen as possible to delay the growth of aerobic micro organisms and reduce the degree of oxidation. However, there are some exceptions. Oxygen helps to preserve the oxygenated form of myoglobin, which gives meat its red colour. Oxygen is also required for food and vegetable respiration.