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Packaging materials are crucial for the quality of the foodstuffs and their shelf life. Many different packaging solutions have been developed to prevent the rapid decomposition that is caused by oxygen, light and bacteria, or by odours from external sources or taste enhancers which come into contact with the product.

Foodstuff manufacturers who must choose between suitable packaging designs and packaging materials have many important decisions to take. What does the product require of the packaging in the way of protection against deterioration in quality due to microbial growth, oxidization, evaporation etc.? How much water vapour must the packaging allow to penetrate? What about the material's transparency, sealing properties, anti-mist qualities, price, or microwave potential?

Foodstuffs today are packaged to counteract physical damage, chemical changes and microbial contamination. It is therefore necessary for the packaging and the pack qualities to be adapted to the requirements of the foodstuff in question. For example, both fresh meats and processed meats to which nitrite has been added are sensitive to oxygen, light, temperature variations and microbial contamination. The surface of non-packaged products will dry out, and the danger of microbial contamination of the product increases. External factors will separately and in combination affect the quality of the product. In addition, the packaging must give the best possible protection of the foodstuff, must have good qualities of transport and storage, and must promote sales. In accordance with regulations, the packaging must give information on the product's name, composition, weight or volume, shelf life, storage method and producer or importer.

Different material properties are combined
Packing materials that are used for all types of MA foods (except fruit and vegetables) should have high barrier properties. Among the polymers that are used are polyester, polypropylene, polystyrene, polyvinyl chloride, nylon, ethylene vinyl acetate and ethylene vinyl alcohol polymer. These are usually laminated or coextruded with polyethylene which comes in direct contact with the product and which is a heat-sealing medium. Great efforts are being made in the field of research to use user-friendly materials both in production and in subsequent combustion, and to optimalize packing material so that as small an amount as possible is used. This is why PVC is more and more often replaced by other materials such as APET (amorphous polyester).

Below is a list of some typical materials that are used along with the products. The exact composition of the film is adapted to the individual product and to the type of packing that is required.

To ensure the retention of modified atmosphere during the lifetime of the pack, many different plastic materials are often combined into a structure with several layers, each layer having its own function. Different plastic materials can therefore be chosen and combined to achieve:

• mechanical strength
• water vapour barriers
• gas barriers
• gas penetrability
• anti-mist properties
• sealing properties

For meat packing, both plastic films with high oxygen transmission such as PE (polyethylene) film, and almost oxygen-proof films such as barrier films made of PVDC (polyvinyl chloride) and EVOH (ethylene vinyl alcohol) are used. The choice of film depends on the packing method and of course on the product. The packaged goods are also packed in an outer or distribution packaging. The outer packaging consists of corrugated carboard boxes of different sizes and thicknesses. Currently, the distribution system in the meat industry uses returnable boxes made of hard plastic.

Some of the most usual plastic materials used for meat and meat products and their properties under standard conditions

(thickness 0.025 mm)

Polymer	Abbreviation	Oxygen ml/m2 24 hours- atm 250C	Carbon dioxide ml/m2 24 hours- atm 250C	Water vapour g /m2 24 hours- atm 370C	Weldability
Polyethylene (low density) (high density)	PE LDPE HDPE	4000-13000	8000 - 80000	14 - 20	Good
Polyester	PETP	500-4000	4000 - 10000	5-10	Poor
Polyamide (nylon)	PA	30 - 110	150 - 400	40 - 150	Poor
Polyvinyl chloride	PVC	100 - 7500	800 - 50000	50 - 100	Poor
Polyvinyliden chloride	PVDC	8 - 26	50 - 150	1 - 5	Poor
Ethylene vinyl chloride	EVOH	0.4 - 0.6 (%RH) 25 - 31	0.5 - 2	40 - 80	Poor
Polypropylene	PP	1300 - 6000	7000 - 12000	8 -14	Poor
Polystyrene	PS	2600 - 8000	1000 - 26000	> 100	Poor
Source: Norwegian Food Research Institute

Examples of plastic films used for packing foodstuffs

The figures give the thickness of the layers in mm.

Underlay	Overwrap, bags	Applications
PA 80 / PA 160	QPA 15 / PE 60	Fresh meat, large pieces (vacuum)
PA 60 / PVDC / PE 100	PETP 15 / PVDC / PE 70	Fresh meat, sausages, meat cuts (vacuum)
PVC 400 / PE 70	PETP 15 / PVDC / PE 70	Fresh meat (gas)
PETP 400 / PE 70	PETP 15 /& PVDC / PE 70	Fresh meat (gas)
PA EVOH PA 40 / PE 105	POET 12 / PE EVOH PE 60	Sausages (vacuum)
	PETP 12 / PE 50 / PVDC	Sausages, meat cakes (gas, flowpack)
	OPA 15 / PE 60	Sausages (gas, flowpack)
	OPET 12 / PE 25 / EVOH PE 29	Sliced meats (gas, flowpack)
	OEVH 12 / PE 60	Sliced meats (gas, flowpack)
	PET / PVDC / PE	Poultry
PET / PA PVDC	PVC / PE	Fresh fish
	PET / PVDC / PE	Pizza
	PET / PE / PVDC	Cheese
	Metallized PET / PE	Dry products such as coffee, milk powder etc.
	Metallized PA / PE	Dry products such as coffee, milk powder etc.
	Microporous film LDPE / OPP / PVC	Fresh fruit and vegetables
Source: Norwegian Food Research Institute

Primary functions of the main materials used
PVDC, EVOH acrylonitrile	O2 barrier
HDPE, PVDC, PP	Moisture barrier
HDPE, PP	Elasticity, microwave possibilities
Nylon	High temperature resistance, flexibility, hardness, moulding strength
CPET	Elasticity, high temperature, O2 barrier
APET	Elasticity, O2 barrier
Polyester	High temperature resistance, flexibility puncturing resistance
PVC, PET, LDPE, HDPE, EVA	Sealing layers
EVA	High O2 and CO2 penetrability