Economic pressures in industry mean that packaging has to be designed using the principle of "as little as possible but as much as necessary”, said the researchers.
They found the lid of some packaging to be ‘over-designed’ and suggest thinner barrier materials can be used than ethylene vinyl alcohol copolymer (EVOH) barrier polymer such as PET while protecting the food.
Modified atmosphere packaging (MAP) systems either come in two parts (a base and cover/lid) or in the form of bags.
A mix of packaged food products with different shelf lives were bought and analyzed at the Fraunhofer Institute for Process Engineering and Packaging IVV.
Oxygen concentration findings
Sven Sängerlaub, head of the functional materials business unit at Fraunhofer IVV, said they did not expect that the permeability of lids and trays of one packaging could be that different.
“Interestingly some products suffer from increased oxygen concentration in the packaging. We assume that oxygen is trapped in the food during processing and thereby carried into the packaging. We always expected such issues but could prove it with our study,” he told FoodProductionDaily.
“Our results confirm that MAP treatment is often not enough to exclude all oxygen from the packaging headspace.
“As mentioned earlier the food contains some oxygen as well. To solve the issue and increase the shelf life the food should be processed in nitrogen or an oxygen scavenger should be applied.”
Low concentrations of oxygen were detected for pasta products, baked goods, sausage products, fish, cheese, snack products, and ready-to-eat meals.
These products need to be protected against oxidation and the growth of aerobic microorganisms using MAP systems with nitrogen/carbon dioxide mixtures or nitrogen.
Concentration of oxygen in packaging for cashew nuts, chipsticks, lasagne, and the baguette with herb butter was relatively high. Possible reasons for this are residual oxygen after the packaging process or too high oxygen permeability of the packaging.
A very high oxygen concentration (75% volume) was measured in the packaging for fresh meat. In this system the oxygen stabilizes oxymyoglobin, the pigment responsible for the red colour of meat.
The low oxygen permeability of packaging material used for MAP systems was low except for fruit and vegetables which require high oxygen permeability.
The clear difference between the oxygen permeabilities of different parts of two-part packaging systems was unexpected and in some cases the oxygen permeability of the bases was one to two orders of magnitude higher than the lids, a weak point which promotes oxidative spoiling and the growth of aerobic microorganisms, said the researchers.
The barrier polymer EVOH has low oxygen permeability and is often used for MAP systems for oxygen-sensitive products and fresh meat.
Polyethylene (PE) and polypropylene (PP) are used as sealing layers due to good sealing properties.
Polyethylene terephthalate (PET) and polyamide (PA) increase the strength and stability of the packaging and provide a medium barrier to oxygen.
Sängerlaub said there is a trend to deliver “one-solution fits many applications”.
“If it is considered that other properties such as sealability, runability and production efficiency are of high relevance it becomes clear that sometimes lids are used that are over-engineered.
“The issue could be seen vice versa: At some application a tray with better barrier properties can lead to a longer shelf life an better product quality.”
Carbon dioxide concentration in packaging varied between product groups. The bacteriostatic effect of carbon dioxide inhibits microbial growth.
Baked goods had much higher concentrations (>50% volume), because there is an enhanced risk of mould growth.
No carbon dioxide was detected in the headspace of packaging for cashew nuts and chipsticks. These are dry products with a low water activity and are less prone to microbial growth and presence of carbon dioxide is unnecessary.
For cost savings the overall packaging processes must be analysed, said Sängerlaub.
“One example is to choose the right sealing polymer which enables faster sealing. Another issue are better adapted thermoforming parameter which lead to a more equal thickness distribution and allow therefore thinner barrier polymer layers.
“Some packaging for sensitive food products with short shelf life are overdesigned. An example is the tray for fresh meat with a shelf life of four to 10 days.
“The modified atmosphere consists of nitrogen and oxygen (e.g. in the ratio 70%/30%). In some cases we found PP trays with additional EVOH barrier. However a PP tray without EVOH is sufficient for fresh meat packed and will keep the modified atmosphere at an acceptable level.”