LPT 321: Meat Science (1+1)

TYPES OF PACKAGING

• Practically all films used for meat packaging derive from synthetic “plastic” materials.
• Even cellulose, formerly widely used in the form of transparent films is no longer put into much use to pack meat.
• The most common synthetic materials used for meat packaging are:

Polyethylene (PE)	(oxygen + , water vapour -)
Polypropylene (PP)	(oxygen + , water vapour -)
Polyvinylchloride (PVC) (soft)	(oxygen + , water vapour -)
Polyester (PET)	(oxygen ± , water vapour -)
Polyamide (PA)	(oxygen - , water vapour +)
+ : relatively permeable
- : relatively impermeable

• Both Polyvinylidene chloride (PVDC) and Ethylene vinyl alcohol (EVOH)
• Foils made from the above synthetic materials are selected based on their different properties related to oxygen and water vapour.
• Packaging films may be conveniently classified into
• Single-layer films or
• Multi-layer films

Single-layer films

• Single-layer films are commonly used in the wrapping of meat pieces, processed meat products, bone-in or boneless meat cuts or even entire carcasses.
• These films are usually self-adhesive, i.e. they cling together -“cling film”- in the overlapping areas.
• Hence they offer good protection from external contamination and to some extent from evaporation, but do not protect from oxygen ingress, as they are not hermetically closed or sealed packages.
• Foils with good self-adhesive properties are polyethylene, polyamide, polyvinylidene chloride and polypropylene.
• Single-layer films are used for freezer storage.
• Single-layer films are stretched tightly around the meat surface prior to freezing tor frozen storage of meat blocks, meat cuts or smaller portions of meat or meat products.
• Since the film is in tight contact with the product’s surface it prevents evaporative losses, commonly encountered freezer storage of unpacked products.
• The tight contact between the product’s surface and the film also prevents ice formation and freezer burn is liable to develop at non contact spots
• Suitable cold resistant films for freezer storage are polyamide and polyethylene.
• Yet another specific utility for single-layer films is the wrapping of chilled meat portions for self-service outlets (supermarkets, etc.).
• The product to be packed is placed in a hygienic cellulose or plastic tray and tightly wrapped with single-layer plastic film. The ends of the foil are overwrapped at the bottom side of the tray, where they firmly cling together.
• Films to be used should have low water vapour permeability to avoid the drying out of the meat during storage, but must possess high oxygen permeability so as to ensure the meat retains its bloom owing to the formation of oxymyoglobin.
• Suitable single-layer films for fresh meat packaging are polyethylene or soft polyvinylidene chloride.

Multi-layer films

• The plastic films used in meat packaging are permeable either to moisture or oxygen.
• Ideally for packaging of meat a combination of oxygen and moisture impermeability is required.
• Hence multi-layer films have been developed in which the film on the outer layer has good mechanical strength and is impermeable to oxygen and the inner most layer is impermeable to water vapour and must possess good sealant properties too.
• The multiple layers may just have two layers or more layers too.
• A very efficient combination is polyamide and poly ethylene.
• The outer layer, polyamide is relatively oxygen proof but permeable to some extent to water vapour.
• Poly ethylene has exactly the opposite properties, it is water vapour proof but permeable to oxygen.
• The combination of both renders such a multi-layer film impermeable to both oxygen and water vapour evaporation.
• Moreover, the poly ethylene used as the inside layer has good thermoplastic properties and is therefore well suited for heat sealing.
• Sealant layers consist mostly of polyethylene or ionomer. Outside layers may be polyamide, polyester or polypropylene (PP).
• Barrier layers for oxygen are made of Polyvinylidenchloride or materials with similar properties.