Packaging of retail food products has evolved rapidly during the past decade in response to the changing needs of consumers, producers and retailers.

The use of modified atmosphere packaging (MAP) started in the UK and US and has spread across Europe, growing rapidly in developing countries like South Africa too.

In the 21st century supermarket, shoppers have rather different needs and priorities to those of 30 years ago; with convenience and quick preparation of meals being high on the list.

In many countries the number of households has increased faster than the population, resulting in the majority of shoppers regularly purchasing food products for consumption by singles or couples. Double-income families naturally enjoy greater disposable income and develop tastes for exotic cuisines.

Attractively presented fresh or prepared foods and combination meals, in durable hygienic packages that offer a useful shelf-life under normal refrigeration, have become very popular - both for everyday consumption and for entertaining.

Consumers have demonstrated a strong preference for chilled fresh foods over frozen, dehydrated, or chemically preserved items, while marketeers have raised expectations of product quality consistent with brand promises that are difficult to maintain.

MAP meets food industry challenges
Faced with these consumer preferences and growing demand for an ever wider range of food products, retailers recognised the need for a revolution in packaging technology.

They needed to simultaneously address their spoilage problem and provide a huge diversity of new prepared foods, but remain competitive by minimising operating costs.

The popular vacuum packaging technology came closest in that the food products were visible in the package, but soft or fragile items were easily crushed and after the exclusion of air, many foods rapidly change in colour and therefore lose their appearance of freshness.

The longer shelf-life provided by MAP technology now gives food processors, manufacturers and distributors better control of the quality, availability and cost of their products.

Reduction in labour and wastage costs can be realised, because less frequent product rotation, removal and restocking are required. Manufacturing capacity has become available for new product development and the range of distribution increased.

Shelf-life and spoilage
Shelf-life may be defined as the interval of time after production, during which a product remains acceptable for consumption. The evaluation of acceptability is based on several factors – the most important of which is safety.

Acceptable food must retain the desired sensory, chemical, physical and microbiological characteristics and also comply with the nutritional characteristics declared on the label, when stored and handled under the recommended conditions.

The shelf-life of food products is influenced by many factors including:
**Quality of raw ingredients

**Product formulation

**Processing method

**Hygiene standards

**Type and integrity of packaging

**Storage and distribution environments

**Consumer handling

Prematurely spoiled packaged foods must obviously be discarded and this waste can erode the profitability of a retail operation. Extended shelf-life can also enhance profitability by increasing distribution flexibility and facilitating centralised processing and packaging.

What is MAP?
The Earth’s atmosphere consists of approximately 78% nitrogen, 21% oxygen, 1% argon, 0.04% carbon dioxide, plus trace amounts of inert gases and water vapour.

MAP encloses food products in a container together with a combination of gases that differs from the normal composition of air.

Typically, MAP packages are sealed by a transparent barrier film that may be selectively permeable to specific gases. Various combinations of atmospheric and other gases have been shown to be effective in shelf-life extension and to enhance the fresh appearance and texture of a wide range of foods.

On a larger scale, a modified atmosphere can be maintained within bulk storage facilities by continuously supplying a controlled flow of gases from storage. This is called Controlled Atmosphere Packaging and also compensates for the natural interaction between food components and the atmosphere after packaging.

It must be emphasised that MAP is designed to extend the normally expected shelf-life of various food products and can not in any way replace or reduce the absolute necessity for adequate temperature control, throughout the storage, processing and distribution stages.

Atmospheric gases
Most popular gas atmospheres used in MAP are composed of varying proportions of the gases found in the Earth’s atmosphere and therefore are completely natural substances.

These gases are also among the elements from which all organic molecules are built, so their use is completely consistent with organic food production.

As the major component of the Earth’s atmosphere, nitrogen has no chemically active role in food preservation, because at ambient temperatures it is generally considered to be inert. It serves two important purposes in MAP: to exclude oxygen and moisture, while providing a source of gas pressure inside the sealed package.

Pressure is required to provide physical protection to the package contents by helping to prevent fragile items like crisps from being crushed or broken during handling and distribution.

Food processors who operate at high-altitude should allow for the increase in atmospheric pressure when goods are transported to lower-altitude locations.

Oxygen in the air causes oxidative deterioration of many foods and also supports the growth of aerobic micro-organisms. These processes can be arrested by sealing the product in an impermeable pack with pure nitrogen gas.

This is widely used for packaging potato crisps and many other snack foods, where the presence of oxygen introduces a risk of rancidity especially with unsaturated oils.

Oxygen meanwhile, is a highly reactive oxidant, often responsible for the rapid deterioration of food products when exposed to air, but when packaging red meat it plays an interesting role by maintaining the appearance of freshness.

A pigment known as myoglobin turns bright red when exposed to an oxygen-rich atmosphere, and this explains why vacuum packed meat often has a dull brown appearance which lacks consumer appeal. Oxygen also inhibits the growth of anaerobic organisms.

Respiration refers to the process by which fresh fruit and vegetables continue to absorb oxygen and release carbon dioxide after harvesting. When sealed with an impermeable film, the oxygen is soon consumed and replaced by carbon dioxide, causing anaerobic respiration and potentially resulting in the development of bad odours, appearance and taste.

It is therefore imperative that a minimum of 2-3% oxygen is maintained inside packs of fresh produce. If barrier film of the appropriate permeability is used, this balance becomes self-sustaining during the shelf-life of the packaged product.

The usefulness of carbon dioxide for packaging fresh foods stems from the fact that it effectively inhibits the growth of most aerobic bacteria and moulds. This property makes it useful for a wide range of foods including bakery products, cheese and other dairy products, fresh produce, fish and seafood, poultry and meat.

Highly soluble in both water and fat, carbon dioxide is readily absorbed by foods that contain these components.

This is problematic in three different ways:
1. Absorption causes the pressure to drop and can result in packages collapsing if it drops below that of the ambient air
2. Drip loss may be exaggerated
3. Dissolved carbon dioxide forms carbonic acid and this can give foods a tainted flavour if they are served cold, whereas heating during preparation expels the absorbed gas

Novel gases
Other gases have shown useful properties for certain applications, but their use is limited by cost and safety considerations.

Carbon monoxide for example; this highly toxic, flammable gas can be used as a more powerful agent than oxygen for producing a bright red pigment in red meat. This practice can be used to mask dangerous deterioration and is banned by several countries including Canada, Japan, Singapore and the European Union (EU).

One of the noble gases and a chemically inert element, argon can be substituted for nitrogen but at significantly higher cost, and its higher density may suit some applications. It is claimed that by inhibiting enzymatic activity, argon is beneficial for packaging fresh vegetables.

Another member of the noble group of gases is helium, but this is not often useful in MAP because of very low density and high cost.

Ozone however, is a very powerful oxidising agent during its short half-life and has useful properties as a disinfectant. An unstable allotrope of oxygen, dissolved in water it is used to wash both produce and equipment to help control microbial growth. In MAP its safe concentration is limited to 15% but is not fully approved in the EU.

MAP & food safety
It is critically important that the implementation of MAP should include appropriate quality monitoring and evaluation procedures.

In many countries legislation requires food producers to follow Good Manufacturing Practice regulations, addressing issues of record-keeping, personnel qualifications, sanitation, cleanliness, equipment verification, process validation, and complaint handling.

Hazard Analysis and Critical Control Point, (HACCP), is a systematic preventive approach to food and pharmaceutical safety based on seven principles that address physical, chemical and biological hazards as a means of prevention, rather than finished product inspection.

The international system ISO 22000 standard includes the seven HACCP principles in a complete food safety management system.