Which packaging film do you need for meat?

Packaging of meat has several functions: it contains the product, protects the meat against deteriorative effects, prevents the meat from becoming contaminated or dehydrated, extends the shelf life, provides space for labelling and facilitates communication to consumers as a marketing tool. Which packaging film is preferred depends on the properties of the material used.
To increase the shelf life of packed meat, it is important to limit the penetration of oxygen through the packaging film for the presence of oxygen increases the growth of aerobic microorganisms. For a longer shelf life, you need a higher oxygen barrier. In addition, dehydration and temperature need to be controlled.  

Oxygen permeability

Packaging films are able to absorb moisture from the environment. Especially polyamide (nylon) can absorb relatively high amounts of moisture. Nylon becomes more permeable for oxygen as the absorption of moisture increases. One method to prevent uptake of moisture by nylon is to use a laminate and encase the nylon in other films which are less susceptible to moisture uptake. When the film is preformed by a vacuum packaging machine, the thickness of the film after preforming must be checked on a regular basis. The oxygen permeability increases in direct proportion to the decrease in the thickness of the film. The most vulnerable places are the corners of the configuration since the stretching of the film at those places is maximal.

Fresh meat

There are different methods for packaging fresh meat: atmospheric, aerobic circumstances such as in a synthetic bag, in (wrapping) film or packaging under modified atmosphere like vacuum packaging or modified atmosphere packaging (MAP).

Atmospheric packaging

Applying atmospheric packaging means no specific change in the composition of the air. The fresh meat is packed in a film with a high oxygen permeability. Using this kind of packaging means that the spoilage organism will be Gram-negative Pseudomonas species. In specific situations, such as meat with a high pH and high storage temperatures, other microorganisms like Brochotrix thermosphacta and Enterobacteriaceae can play an important role in spoilage. Perishability/decay of meat packed in wrapping film becomes observable by the formation of odour abnormalities, discolouration and mucus. The discolouration increases when the amount of microorganisms is above 107 per cm2. Deviation in odour and formation of mucus/slime can occur when the number of microorganisms reaches 108 per cm2.

MAP

Using MAP starts with removing the air in the pack followed by addition of a composed gas mixture. The most commonly used gas composition for meat in MAP is a mixture of 20-40% CO2 and 60-80% O2. The presence of CO2 inhibits the growth of Gram-negative microorganisms, the spoilage organism of aerobically stored fresh meat. The presence of a high concentration of O2 guarantees a good and steady colour. This technique makes it particularly suitable for packaging consumer units. The spoilage flora of MAP meat often consist of lactic acid bacteria and Brochothrix thermosphacta. The decay is observable by discolouration, an ‘off’ smell and formation of slime when the amount of microorganism is 108 per cm2 or higher.

Vacuum packaging

In the case of vacuum packaging, all the air is removed. This kind of packaging is used for fresh cuts of meat. By using vacuum packaging, the oxymyoglobin will be reduced to myoglobin by the reducing enzymes present in the meat. This gives the meat a purple-red colour.

When the vacuum-packed meat is opened, the bright red oxymyoglobin colour comes back again, but for a shorter period of time. The purple-red colour is less attractive for consumers compared to the bright red oxymyoglobin colour of fresh meat, especially when it is compared to MAP meat or in meat wrapped in film. Instead of an odour of decay, the smell which arises from vacuum-packed meat is an abnormal, slightly sour smell. Furthermore, the decay is characterised by a pH decrease and sometimes by formation of gas and/or mucus.
In general decay phenomena of vacuum- and atmosphere-packed fresh meat is observable when the respective spoilage bacteria exceed 108 per gram per cm2.

Active packaging

Developments continue in the field of active and intelligent packaging of fresh meat. ‘Active packaging’ is based on a technology whereby a particular component on or in the packaging absorbs or releases another component with the aim of improving the quality, extending the shelf life and/or improving the safety of the packaged product. There are several active packaging systems on the market: systems in order to absorb moisture, packaging with antimicrobial properties, CO2 delivery systems, O2 scavengers and film with anti-oxidative properties. Research into the improvement of active packaging with anti-microbial properties, such as the application of nisin, in combination with other preservatives is in progress. The use of natural extracts and essential oils in the packaging of meat also provides new perspectives. Those extracts are rich in phenolic components with strong antimicrobial and antioxidant properties.

Intelligent packaging

‘Intelligent packaging’ is designed to control the condition of a packaged foodstuff. In an intelligent packaging system indicators located in or on the pack register changes to the packaged product or its environment, often visually.
Examples are time/temperature indicators, freshness indicators or oxygen indicators. The time/temperature indicator changes the recommended shelf life of the product. The freshness indicator indicates whether any chemical changes in a packaged product have occurred.
The most common concepts are based on the occurrence of metabolites or changes due to microbiological activity. For a long time, the challenge was how to measure the low concentration of the resulting metabolites, but this now appears to be more feasible.

Recent research

In 2013 Strydon P. et al (Animal Production Institute, South Africa) published the results of an investigation into three types of packaging for beef. Beef steaks were vacuum-packed in shrink bags, ripened for two weeks, and were then re-portioned and vacuum-packed for one week. A second set of beef steaks was vacuum-packed in shrink bags and stored for three weeks. The third set of steaks was preserved for three weeks in vacuum-skin packing. After the three weeks of storage under identical conditions, the third method of packaging was shown to result in less loss of moisture and a redder colour (higher oxymyoglobin concentration). Moreover, after three days of presentation a higher blooming capacity of the meat in the vacuum-skin packaging was ascertained.

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Overview of properties various packagingmaterials for meat and meatproducts