Oxygen barriers are normally stated as OTR (Oxygen Transmission Rate), a measurement of the transmission of oxygen through the packaging material. The presence of oxygen leads to quality impairments such as undesirable microbiological growth, rancidity, discolouration and loss of nutrients in many food products. When the products are also exposed to light, many of these undesirable processes become even faster.
The different types of plastic vary greatly in their barrier properties against different gases. Oxygen transmission in the packaging is very important for oxygen sensitive foods. Using the OTR value (ml O2/m2 24 hr, 1 atm) as a basis it will generally be possible indicate the properties of the oxygen barrier:
Good: 10-100
Very good: 1-10
Extremely good: <1
Oxygen enters through folds and seals (welds) after the packaging has been closed, through damage to the packaging material and through the packaging itself.
Oxygen transmission is different for different plastic materials. Oxygen transmission in packaging materials generally increases with increased temperature and some materials are also affected by surrounding humidity.
What happens when packaging lets in too much oxygen?
- half-baked bakery goods and cheese grow mould
- fresh meat products and jams become discoloured
- fresh products with a short shelf life are spoiled by undesirable bacterial growth
- sliced meat turn grey under the shop lighting
- products with a high fat content like oils and snacks become rancid, especially when exposed to light
It is important to point out that many products can deteriorate even without leaks in the packaging. If the packaging machinery is not working properly and leaves too much residual oxygen after packing, sufficient oxygen will be available in the pack to start undesirable chemical reactions or to allow mould to grow.
