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Carbon Monoxide in Modified Atmosphere Packaging

Jaime Luján Zilbermann
Over the past few months, a controversy has raged in the US over the use of carbon monoxide (CO) in modified atmosphere packaging (MAP) for meats. To bring everyone up to speed, MAP uses hermetically sealed trays to package meat within a mixture of gases different from that in the normal air that we breathe.

Over the past few months, a controversy has raged in the US over the use of carbon monoxide (CO) in modified atmosphere packaging (MAP) for meats. To bring everyone up to speed, MAP uses hermetically sealed trays to package meat within a mixture of gases different from that in the normal air that we breathe.
Shelf life before modified atmosphere packaging
As anyone who purchased meat before MAP was introduced can remember, red meat would turn from a bright red colour to a deep purple and eventually brown. In the case of chicken, this would go from pale beige to darker beige and finally reaching a colour close to grey. The change in colouration simply meant that the meat had had a longer exposure to air, which, since it contains oxygen, had oxidised the heme proteins in the muscles, thus changing its colour. However, many consumers were turned off by this colour change, associating it with the meat "going bad", and would not buy the product, in spite of the fact that it was microbiologically safe to eat it.
How modified atmosphere packaging works
The idea behind the MAP concept is to allow meat to retain the colours most people identify with freshness for a longer period of time. How is this accomplished? Basically by reducing the amount of oxygen in the package, so that the meat oxidises more slowly and replacing with other gases that had no effect on meat colour. So far so good, right? However, because there was always some oxidation taking place, the meat would eventually change colour, although at a later point in time.
Can carbon monoxide make rotting meat look health?
But what if we could make meat retain its fresh colour for as long as it remained in the package? This is where CO comes in. This gas, even in very small amounts, has the peculiar ability of allowing meat in MAP to retain its original colour, even if it has begun to rot. And therein lies the problem: what if consumers, thinking that the meat in a package is fresh because it still has it original colour, decides it is therefore okay to eat and then becomes ill from food poisoning?
This theoretical scenario is what prompted the EU to ban the use of CO in MAP for meat and for consumer groups in the US the raise the alarm after its use, based on scientific research , was approved by the US government. The controversy continues to this day, with different organisations and bodies taking different sides. For example, several supermarket chains and meat processors have announced that out of concern for the body public, they will refrain from selling meat products with CO in MAPs.
CO in modified atmosphere packaging approved in Norway
However, is this theoretical scenario actually probable? As any statistician will tell you, anything is possible, but it is worth looking at what has happened in countries that have approved the use of CO in MAPs, such as Norway. Last year, in my former role as editor of Meat International, I was invited to visit the Norwegian Meat Research Centre, where, among other subjects, we discussed CO in MAPs.
How protected do consumers need to be
According to the researchers at the Centre, certain important aspects from that theoretical scenario are missing. First, MAPs have a date of expiration printed on the package. That date has a purpose, pointedly, to tell consumers when they should eat the meat. And second, that when meat begins to rot, even if it's packaged in a modified atmosphere, it will produce a literally rotten smell. These two points have prevented Norwegian consumers from falling ill from eating bad meat because they have learned that the expiration date is there for a purpose.
In light if this, it seems we need to ask ourselves the question, just how stupid do we think consumers are? It seems quite obvious that consumers can read expiration dates and can tell the difference between meat that is still safe to eat and rotten meat just by following their noses. So, are consumer groups that stand against the use of CO in MAPs really protecting consumers (who they say they represent) or just crying fowl because they are afraid of change? It seems science and experience are against them…


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    Robert Wuthrich

    I fully agree with you. The expiration date though should not be a sticker, but directly printed on the plastic foil to prevent any "re-dating", as it happens sometimes in South America.

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    Waqar Ahmad Pakistan

    Why at all use CO as MAP if expiry date is printed there.That is the only criterion for health no matter colour changes. Instead they write extra that colour may change with certain time but safe untill the expiry date.We save time while packaging and money incurred.Less costly.What anout Nitrogen as MAP

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    Ruth Kamenev

    What other benefits does using CO in MAPS have - I am wondering if the lack of oxygen in the packaging atmosphere reduces or slows down the growth of bacteria in the meat, thereby reducing spoilage. ie Does it lengthen shelf life as well as improve colour? Another question - is the expiry date on a package of processed meat good only if the package remains unopened or is it good even if the package is opened? Please comment.

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    Jaime Luján Zilbermann

    With regards to Ruth Kamenev's question as to whether CO reduces or slows down the growth of bacteria, that would depend on the mixture of gases; CO is never used as the only gas within the package.
    As to the second question, the expiration date only refers to the unopened package; the gas mixture ceases to have a preservative effect once the package has been breached.

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