The mixes of map

The mixes of map – modified atmosphere packaging

Claudia D. O’Donnell

Mix 78.08% [N.sub.2] (nitrogen) with 20.95% [O.sub.2] (oxygen). Throw in a pinch (0.035%) of C[O.sub.2] (carbon dioxide), and you have a priceless, albeit free, commodity known as air. Although this mix works fine for organisms from humans to trees, packaging foods under altered ratios provides an array of beneficial effects – as well as a few concerns.

In modified-atmosphere packaging (MAP), air is replaced in a pack by either a single gas or a gas mixture. No further control is exerted over the gas composition, even though it may change due to microbial respiration or gas transmission through thepackaging film.

In controlled-atmosphere packaging (CAP), the original gas composition in a package is maintained by various technologies, ranging from gas scavengers (e.g., iron oxide contained in packets) to “intelligent” films, which allow selective gas transmissions.

KUDOS FOR GASES

Despite the availability of other gases, oxygen ([O.sub.2]), carbon dioxide (C[O.sub.2]), and nitrogen ([N.sub.2]) are still the ones most commonly used for MAP. Some companies have also begun using argon, notes Joseph Regenstein, a professor at Cornell University.

In and of itself, oxygen’s most detrimental effect on a food’s shelf life is through lipid oxidation. Oxidative reactions can be slowed when products are packaged under either a vacuum or [N.sub.2] gas in order to create the reduction or absence of oxygen. This potentially reduces rancidity in products from cured meats such as bacon to snacks and nuts; warmed-over flavor in cooked poultry and meats; and off-flavors in fatty fish.

The food industry has been most intrigued, however, with the use of MAP to extend the shelf life of foods vulnerable to microbial spoilage.

For fresh meats, fish, poultry, produce, dairy products and partially or fully precooked prepared foods, temperature reduction is the most important factor in microbial control.

However, when [N.sub.2] replaces [O.sub.2] (as the only change), growth of aerobic spoilage microorganisms – including molds is inhibited. To be effective, levels of [O.sub.2] far below 1% must be achieved, says Aaron Brody, managing director, Rubbright. Brody, a consulting firm in Devon, Pa.

Strong bacteriostatic effects against both aerobic and anaerobic microorganisms are obtained through use of high levels of C[O.sub.2]. The mechanism is not completely understood and may involve factors such as pH reduction (through the formation of carbonic acid when C[O.sub.2] reacts with [H.sub.2]O) or actual toxicity of the gas.

Determining the appropriate C[O.sub.2] level provides a challenge. Very high levels of carbonic acid can have undesirable effects on a food’s sensory attributes. Additionally, C[O.sub.2] is very soluble in fats and water. A package’s headspace volume will decrease as C[O.sub.2] is “absorbed” into a food. This can be used to an advantage when a processor wants a packaging film to “cling” to a food’s surface. Using [N.sub.2] in combination with C[O.sub.2], minimizes these effects.

Due to concerns that anaerobic atmospheres will suppress natural flora growth and allow Clostridium botulinum to proliferate (without indications of spoilage), [O.sub.2] is often included in a gas mix at high enough levels so as to deter this.

Regenstein says he and others have demonstrated that MAP atmospheres of high C[O.sub.2] (for bacteriostatic effects) with high levels of [O.sub.2] (to prevent growth of anaerobic microorganisms) extend the shelf life of lowfat (white) fish.

“Fresh-cut vegetables is probably the fastest growing sector in retail food today with 74% growth in 1994 to over $340 million,” asserts Brody. This is also one of the hottest areas for MAP as well.

For example, respiring fruit and vegetable tissue – whether in whole produce or partially prepared products – generally benefit from less than 10% [O.sub.2] and less than 20% C[O.sub.2] to control microbial growth. An atmosphere of 1-2% [O.sub.2] and 5-10% C[O.sub.2] has been recommended for broccoli.

One change in U.S. labeling law could encourage further MAP growth in the poultry industry, as well. If processors are no longer allowed to label previously frozen poultry as fresh, there will be an incentive to revisit MAP as an alternative way to extend shelf life, says Regenstein.

FUTURE DEVELOPMENTS

There are two primary areas of research, says Brody. First, interest grows in shipping containers that control temperature, humidity, [O.sub.2] and C[O.sub.2]. The military and produce exporters have led this area.

Second, efforts are being directed toward confirming or denying the safety of reduced [O.sub.2] atmospheres.

It is this second area that provides the greatest impediment to continued MAP growth. Perhaps the greatest concern is reserved for products such as precooked entrees – in which bacteria that would compete with pathogens have been eliminated. However, all foods relying on refrigeration as the primary hurdle to microbial growth are closely watched.

For example, “Although Europe has not had problems with MAP, the U.S. government has never really come to terms with it in respect to seafood,” says Regenstein.

The U.K.’s Sea Fish Industry Authority has recommended use of a gas composition of 30% [O.sub.2], 30% [N.sub.2], and 40% C[O.sub.2] for lowfat (white) fish. However, “In the U.S., the National Marine Fishery Service has only approved one system for modified-atmosphere packaged fish, and storage at 28 [degrees] F is required,” he says.

Future activities in the area of MAP will not only involve safety concerns.

Bob Hart, manager of food technology at Leatherhead Food Research Assoc. Surrey, U.K., predicts key developments to watch:

1. Sensors that will indicate a pack’s gas composition. This will assure that the original gas mix is correct, that leaks are detected, and any changes can be monitored.

2. Packaging films with permeabilities that change with temperature in order to match fruit and vegetable metabolism. Permeabilities will increase with higher temperatures to allow C[O.sub.2] (produced by respiration) out while allowing [O.sub.2] in.

3. Films which incorporate functional components such as oxygen scavengers, anti-microbial agents, and so on.

RELATED ARTICLE: Prepared Foods R&D Investment Survey

In the 1995 Prepared Foods R&D Investment Survey, 18% of the 736 companies said their R&D programs would increase activity in the area of MAP/CAP, although interest varied greatly among food categories. Companies whose primary sales are in the category of prepared meat, fish and poultry or in the category of prepared vegetable and fruit products showed the most enthusiasm, with 27% and 24% saying they would be increasing their R&D activity in this area respectively.

RELATED ARTICLE: INSIGHTS AND OUTAKES

“HACCP can include nutrition under some circumstances, for example, long-range feeding programs for a ‘captive’ audience such as a prison population.”

– Oscar [Pete] Snyder, president, Hospitality Institute of Technology and Management

“Our macaroni salad label looks [as lengthy] as War and Peace.”

– Steve Loehndorf, vice president of technical services, Orval Kent Foods, commenting on NLEA regulations requiring ingredients in mayonnaise, mustard and relish to be detailed in ingredient statements, as quoted in PF 4/95, p. 31.

COPYRIGHT 1995 Business News Publishing Co.

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