News reports within the last day or two have revealed that some of New Zealand’s meat undergoes a process called ‘gas flushing’, in which carbon dioxide and oxygen are pumped into meat packaging to significantly lengthen the meat’s shelf-life.
Meats which have undergone the process, also called Modified Atmosphere Packaging (MAP), are not currently labelled as such, and the practise is used only by some of New Zealand’s food retailers.
The SMC approached local experts for comment on the practise, and its effects on the quality, nutrition and safety of meat.
Associate Professor Jonathan Hickford, President of the New Zealand Institute of Agricultural and Horticultural Science at Lincoln University, comments:
“This would be an issue if we actually could define the “value” of “fresh meat”.
“Everyone wants meat (and in fact anything else in the supermarket) to be safe and in that respect we are reliant on the NZFSA to set and monitor industry requirements. They are required by Australasian law to do their job well. It appears that the safety of the gassed meat is beyond reproach. In this context, bacterial safety is probably of most concern – but that is the purpose of these gassing techniques – they are designed to limit bacterial spoilage, while enhancing meat quality.
“Gassing per se is not unique in that meat preservation technologies have existed for thousands of years, from things as simple as drying and salting, through curing and canning to gassing and use of other preservatives. Just because something is old doesn’t mean it is undesirable or less valuable. Perhaps one of the best examples being Parma ham, where the pig meat is essentially salt cured (uncooked) and then dried for 18 months or more. It retails for $400-600 for a leg, or about $75 per kilogram. Age isn’t an issue and there is apparently little relationship between age and quality in the broader meat market.
“On the positive, the prolonged storage of gassed meat may assist the meat tenderisation process. Export chilled (not frozen) meat products “condition” in cool storage as they are transported by ship to overseas markets. They command the market premium in those markets.
“On the negative, consumers need to always be aware of the risk associated with the consumption of high levels of saturated fat, as is typically the case with any meat.
“This all stated – Sue Kedgley is undoubtedly correct. The consumer always has a right to know and in this respect all food suppliers need to be able to describe and prove the safety and quality of their supply mechanisms. This isn’t just meat specific and the same is true of any food or beverage. Whether this information can be effectively “put on a label” is another issue and one that is grappled with all the time in the food sector.”
Dr Roy Bickerstaffe, Professor of Food Biochemistry and Chair of the Lincoln University Research Committee, comments:
“Gas flushing or gas packing is known as MAP or modified atmosphere packaging. It is widely used in the food industry for packaging products to preserve them longer in the modified atmosphere. This has two effects – usually the products retain their appearance and their shelf life is extended. This is important for NZ exporters, who will often pack products in MAP
“You can use several types of gas mixtures. To preserve a product, you nomally replace oxygen that can spoil the product with an inert gas such as nitrogen or carbon dioxide. To use MAP you need the correct type of plastic packaging: one that seals to retain the gases.
“All the above revolves around costs,time intended to hold the product,turnover of product transport time from processing to retail etc
“Gas packing has no adverse nutritional or health issues through causing changes in the product. Food Safety in NZ and the FDA in the USA have approved gas packing but stipulate the levels that might be used.
“In the stated case with meat they have chosen the carbon dioxide and oxygen mix on the grounds that the oxygen is at a level to bloom the meat and carbon dioxide to balance out and extend the shelf life.This is offset by the cost of packaging and the marketing call this group has made versus another operator that relies on normal packaging, normal blooming and turnover of their shorter lshelf life product
“The real important issue, in my opinion, is the use of carbon monoxide. The FDA in the USA allow it at very low levels but in Europe (particularly Germany) carbon monoxide is not allowed on the grounds that there may be leakages on storage of quantities of the packaged product, so they state ‘why put the public at risk?’.”
Dr Brian Wilkinson, Senior Lecturer at the Institute of Food Nutrition and Human Health at Massey University, comments:
“Unfortunately, Lois Cairns [article here] has got her wires a bit crossed and has failed to capture the slight nuances in the packaging of meat. The New Zealand industry uses three methods of packaging its meat, namely: polyethylene overwrap (Shrinkwrap), vacuum packaging and modified atmosphere packaging.
“There are two forms of modified atmosphere packaging: high oxygen modified atmosphere packaging and high carbon dioxide atmosphere packaging. In the latter case there is virtually no oxygen in the pack. Meat that is sold on the local market is either packaged in polythene overwrap or packaged in an atmosphere that contains 70-80% oxygen and the balance carbon dioxide. The companies supplying the local market most often pack their meat in polyethylene overwrap.
“The meat is placed on a polystyrene tray and then covered with Shrinkwrap. This meat has a maximum shelf life of 7-10 days depending on the microbial numbers at the time of packaging. As the author of the article stated most supermarkets sell their meat in this fashion. Countdown, on the other hand, sell their meat in a high oxygen atmosphere deep draw pack.
“The export meat industry exports our meat in either a vacuum pack or in a high (99.5 – 99.00%) carbon dioxide pack. In recent years there has been a move away from high carbon dioxide packs because the carbon dioxide that has dissolved in the meat starts to come out of the meat when it is repackaged in a high oxygen pack by our overseas importers. High oxygen atmosphere packaging of meat is extremely common in the USA, Europe and South East Asian supermarkets.
“To my knowledge there has not been a single case of food poisoning over a period of 30 years in any of the aforementioned markets from the consumption of meat that is packaged in high oxygen atmosphere packs. New Zealand has been exporting high carbon dioxide atmosphere packs of meat for over 25 years and likewise there have been no reported cases of food poisoning from the consumption of this meat. The country has been exporting vacuum packaged meat for almost 40 years and here too there have been no reported cases of food poisoning. The modified atmosphere packaged meat, like Shrinkwrapped meat, needs to be cooked to 65oC or higher to kill any pathogens on the meat. Meat companies are reluctant to pack their meat with carbon monoxide because of the safety dangers to workers who may be exposed to carbon monoxide in packing rooms.
“The maximum shelf life of the meats packaged in the various ways is shown below:
– Polyethylene overwrapped 7 – 10 days (local retail sales
– High oxygen modified atmosphere 3- 4 weeks depending on meat type. Colour deterioration, rather than microbial spoilage limits the shelf life of meat (local retail sales)
– Vacuum packaged 6-10 weeks depending on meat type and storage temperature (most NZ meat exported as vacuum packaged)
– High carbon dioxide atmosphere packaged meat 10-14 weeks depending on meat type and storage temperature (usually less because supermarkets expect 4-5 day display shelf life after meat has been repackaged.
“High oxygen modified packaged meat is equally and in most cases safer than polyethylene overwrapped meat. In the case of the polyethylene wrapped meat the packaging film plays no role in safeguarding the consumer from the food borne disease causing bacteria on the meat, other than to prevent further contamination from the supermarket and home environments. Pathogens such as salmonella, listeria and campylobacter can happily grow on the meat and so it is possible for food poisoning to be a problem in the home if good hygienic practises are not followed in the home when the meat is unwrapped and prepared for cooking.
“High oxygen atmosphere packaged meat, on the other hand, does control the growth of food poisoning bacteria. The high oxygen content suppresses the growth of strict anaerobic bacteria such as clostridium botulinum. These dangerous bacteria cannot tolerate the high oxygen content of the packs. The high carbon dioxide content (20-30%) in these packs controls the growth of aerobic pathogens. For instance in the case of salmonella the high carbon dioxide content of the pack atmosphere partially inhibits salmonella growth, as with E.Coli. However, as with all the forms of packaging meat will only last for the times shown above if the temperature is kept close to 0oC.
“It is unlikely that supermarkets would package their meat in meat packs that would have a shelf life of more than a month because it costs huge sums of money to keep a month’s inventory of meat. The costs of storage is at least 10cents/kg/month. But the greatest cots is the meat itself. The export meat companies need the long storage because they have to store the meat here in New Zealand until there is a ship to transport it, then the ship make take 3-4 weeks to get to Europe, then there it takes up to 10 days to get the meat from the wharf to the cutting operation and then they need a further week of shelf life for displaying the meat in the supermarket.”
The New Zealand Food Safety Authority comments:
“Changing the ratio of gases in packaged food and other products to reduce spoilage or otherwise protect the contents has been an accepted and proven international practice for many years. Modified atmosphere packaging (MAP) is used in both retail packaging and internationally in the transport of chilled meat exports. The Meat Industry Research Institute of New Zealand (MIRINZ) was a world leader in the development of MAP for meats in the late 80s and early 90s for maintenance of meat quality and safety over extended storage periods. Reducing spoilage has the potential to reduce wastage and the associated financial and environmental costs, while maintaining food safety.
“Most spoilage bacteria intake oxygen and produce carbon dioxide – just as people do. By reducing the level of oxygen (and increasing the level of carbon dioxide) the growth of these bacteria is greatly slowed. The small amount of oxygen present means other organisms, which can’t grow in the presence of oxygen, are also controlled.
“The Australia New Zealand Food Standards Code sets requirements for the use of processing aids such as oxygen and carbon dioxide that ensure food safety is maintained.
“Different ratios of gas may change the appearance of meat and make it appear less attractive to the buyer. Producers must balance the need to suppress spoilage microbes with the desirability of the product. Fresh meat appears red because oxygen interacts with the natural pigments (myoglobin). But under low levels of oxygen or a high concentration of CO2, meat turns a purple-red colour which, though still safe to eat, is not as desirable. The bright red colour returns quickly on exposure to air when the package is opened.
“MAP does not completely eliminate pathogens, and without spoilage microbes, there are fewer obvious signs of decay (eg, it smells ‘off’ or is discoloured) to indicate the food may be unsafe to eat.
“All MAP meat must be labelled with a ‘best-before’ or a ‘use-by’ date. The best before date is recommended for meats that are cooked before consuming and is a guide to when the product will begin to deteriorate. A use-by date is used when a product can become unsafe which means once a use by date has expired, you should not consume the food even if the package is intact. It is illegal to sell food past its use-by date.
“Most MAP meat still requires strict temperature controls, so storage instructions are essential. Cooler temperatures help control any growth of micro-organisms and also improve the effect of the MAP gases on bacteria. If the food is kept under the recommended conditions, it will be safe to eat until the use-by date is reached.
“Most MAP foods need to be kept in the fridge because cool temperatures keep pathogen growth in check. Pathogens such as Clostridium, Listeria and Aeromonas can still grow in packages with little or no oxygen, and fridge temperatures stop them multiplying to dangerous levels.
“Once the package is opened, the label should instruct you on how to store the food, and how long the food will remain safe under these conditions (eg, “refrigerate upon opening”, “consume within two days”).
“Meat stored in MAP packaging can be cooked and used the same as meat packaged any other way. MAF (Food Safety) is not aware of any accepted science that suggests any significant change in the nutrition value of meat stored this way.”
The New Zealand Food Safety Authority has a factsheet on MAP, which can be found here.