PACKAGING SOLUTIONS
(through MAP) and replacing with carbon dioxide and nitrogen gases has a dual effect. Eliminating oxygen prevents the growth of strictly aerobic bacteria, some of which are potent spoilage microorganisms, whilst carbon dioxide is itself antimicrobial, helping slow the growth of many microorganisms. However, by removing oxygen, the growth of anaerobic microorganisms may be favoured – lactic acid bacteria may become a prominent spoilage microorganism, and pathogens such as non-proteolytic Clostridium botulinum (C. botulinum) may, if present, be able to grow. Alongside considerations and constraints
relating to C. botulinum, other relevant microorganisms and risks must also be factored into shelf-life determination. For example, Listeria monocytogenes can also grow under MAP conditions, and other microorganisms may be able to survive.
What are the impacts of freeze-thaw/ frozen distribution on MAP products? There has been a limited amount of research in this area, but one of the main considerations of thawing a product could be a resultant increase in available moisture, which could affect carbon dioxide absorption and therefore shelf-life.
How much residual oxygen do I need in my MAP pack? Oxygen is usually removed from the pack, particularly with dried foods and those with high fat contents, to reduce oxidation and inhibit aerobic microbial growth. In terms of a residual oxygen level to aim for, this should be as low as possible for maximising shelf-life in oxygen-sensitive products. Gas packing relies on a continuous
stream of gas being injected into the pack to replace the air. The disadvantage of gas packing is that the residual oxygen levels can be higher, which make it an unsuitable method for oxygen-sensitive products. Compensated vacuum can be slower as it is a two-stage process, but the residual oxygen levels are usually lower. Whatever your packing method for minimising oxygen, the level achieved will depend on the efficiency/ effectiveness of the packing equipment. The way residual oxygen is measured
(particularly the timing of the testing) is also a factor. Oxygen can be both released and absorbed by the product inside the pack at different stages of its life. To fully understand the oxygen level
in your pack, this should be measured after a delay (rather than straight after packing) and throughout shelf-life when conducting shelf-life studies.
Why is my MAP pack blowing (or collapsing)? The most common reason for a blown pack is the production of carbon dioxide by microorganisms growing in the product, typically yeast and/or lactic acid bacteria. Collapsing packs, on the other hand, are usually due to the use of high levels of carbon dioxide. Its solubility makes it susceptible to absorption by fat and moisture within the product. Nitrogen is often included in gas mixes to prevent this issue. Oxidation causes oxygen absorption, as
does oxygen usage by microorganisms – both of which can reduce the amount of gas volume in the pack and lead to a collapsing pack.
Using the right packaging to be able to hold the gas inside, without escaping, is also important to prevent pack collapse. Products packed in a modified atmosphere require the materials to have specific barrier properties and maintain seal integrity for the duration of the shelf-life of the product, or the modified atmosphere will be lost. This is important when looking to move to changed or new packaging materials, which must provide equivalent properties to ensure the quality and safety of the product is maintained.
Can I reduce the amount of carbon dioxide used in my MAP pack? With carbon dioxide shortages being a common issue affecting the food and drink industry, it is pertinent to understand the impact of reducing the level of carbon dioxide in your product’s MAP gas mixture.
38 • KENNEDY’S BAKERY PRODUCTION • APRIL/MAY 2026
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