High oxygen Modified Atmosphere Packaging

Packing in high oxygen is a relatively new and novel concept with food products other than red meats.

Oxygen is a colourless, tasteless and odourless gas and although not flammable, it vigorously supports combustion. The use of High Oxygen gas mixtures in the Modified Atmosphere Packaging (MAP) of fresh fruits and vegetables, has been looked at principally from an academic standpoint. Few commercial applications exist, and this technology has to date not been fully exploited, possibly due to mixed results.

From those studies that have been carried out with high oxygen MAP, results indicate that high oxygen can be effective at inhibiting enzymic discolouration, prevent anaerobic fermentation reactions and inhibit microbial growth (CCFRA R&D Report 125). It is hypothesised that high oxygen levels damage the vital cellular macromolecules of micro-organisms, inhibiting microbial growth. However, Amanatidou et al. (1999)* suggests that E. coli and L. monocytogenes can be stimulated by O2 levels of 80 - 90%. High oxygen is also thought to hinder polyphenol oxidase, the enzyme responsible for discolouration of prepared fruit and vegetables (CCFRA R&D Report 125).

An EU Fair project on ‘Novel MAP for fresh prepared produce’ included a number of trials with fresh produce and high oxygen packing to determine the effects on the quality and shelf-life of the products. Products included lettuce, melon, strawberries and beansprouts. The trials indicated that high oxygen has beneficial effects on the sensory quality of a number of different fresh produce products but was not suitable for all products.

High oxygen trials were also carried out on combination products including pizza, sandwiches and stir-fries. Generally combination products are packed in a modified atmosphere with 30% carbon dioxide and 70% nitrogen, however under these conditions anaerobic micro-organisms can grow at temperatures above 3°C. Packing in high oxygen (80-95% O2) can inhibit the growth of anaerobic and aerobic micro-organisms as shown in Figure 1.

The exact mechanism for high oxygen activity is still uncertain, although it is thought that the reactive oxygen species damage vital cellular macromolecules and thereby inhibit microbial growth. Also it is hypothesised that high oxygen levels may cause substrate inhibition of Polyphenol oxidase, which is the enzyme responsible for discolouration.

Figure 1:
Hypothesised inhibition of microbial growth by high O2. (Source: CCFRA R&D Report 125)