Food Protection Connection: MAP Packaging: It's in the Air

(reprinted from Dietary Manager, May 2003)

A fast-growing trend in food packaging today is modified atmosphere packaged, a term you may know by its three-letter shortcut: MAP. According to industry statistics, billions of packages of MAP-packaged foods flood the marketplace today.

MAP packaging allows processors and distributors to provide food that is fresh, convenient, and often less labor-intensive than traditional foods. The leader in the MAP foods category is fresh, ready-to-use vegetables, such as bags of pre-trimmed, pre-washed salad, or packages of washed, sliced mushrooms. Or, consider dip-ready celery sticks, mini carrots, and broccoli. Other examples of popular MAP foods include Lunchables, fresh pasta, fresh pizzas, grated cheese, sandwiches, and meats.

The MAP Appeal

Like general consumers, foodservice operations enjoy the convenience of MAP foods. In fact, one of the early users of MAP was McDonald's Corp., which began distributing MAP-packaged bulk salad to its retail outlets years ago. Some foodservice managers compare the added cost of buying pre-prepped vegetables with the labor cost of in-house prep. . . and choose "ready" produce as a way to contain the budget.
Meanwhile, analysts say that on an average day, the average consumer spends 2 ½ hours less today than a few decades ago in the task of meal preparation. Fewer households have an adult at home today to serve as homemaker and family chef! Even finding time to go to a supermarket can be challenging for many of us with hectic lifestyles. MAP foods not only save prep time, but they also last longer in the refrigerator. In all, MAP packaging boosts storage life by two-to-five times. Thus, it's easier for shoppers to stock-up and reduce grocery trips.

The Technology

What exactly is MAP packaging? In this process, a mixture of gases replaces the ordinary air in the food package. No magic recipe dictates the gas mix. Instead, food technologists decide on a mix and packaging solution for each individual product. In itself, applying MAP technology is a science.

Three gases used in MAP are: carbon dioxide, nitrogen, and — on a limited basis — oxygen. In general, technologists use the carbon dioxide to replace oxygen. This creates a low-oxygen environment, where many foodborne pathogens cannot thrive. The low-oxygen environment also inhibits spoilage by preventing growth of molds and yeasts.

Nitrogen likewise serves to displace oxygen. It's also a "filler" gas. For example, a package of salad needs to stay "puffed up" to protect fragile greens. Nitrogen helps maintain this mechanical protection. Oxygen enters the picture as a way to improve food appearance and typically appears in a MAP food at a proportion of 1-5%. Red meats, for example, need some oxygen to look red and appeal to consumers. In addition, technologists keep some oxygen in the mix to prevent growth of anaerobic pathogens, such as Clostridium botulinum.

Once a food is packaged, its atmosphere can continue to change. In particular, cut produce still "breathes," producing more carbon dioxide in the package. This natural "breathing" gradually brings on a spoilage process. A reduced-oxygen environment slows down breathing, which in turn delays spoilage and extends storage time for produce.

Technologists control the atmosphere of packaged foods not only through the initial mix of gases, but also through selection of packaging materials. Plastics for packaging can vary in the extent to which they seal-in the product atmosphere. New packaging films incorporate technologies such as oxygen-scavenging (which finds and destroys oxygen), as well as packaging compounds that inhibit growth of bacteria.

Safety Considerations

In general, industry experts consider MAP packaging to be very safe. However, because the packaging process does not flow from a single standard, there can be variations based on individual products and techniques. Researchers confirm that in an environment too low in oxygen, anaerobic bacteria such as Clostridium botulinum can flourish. One study focused on shredded cabbage and identified Clostridium botulinum in 0.3% of retail packages. Another study identified Clostridium spores (not the toxin) in about 36 of 1,000 packages of retail, MAP-packaged produce. Listeria bacteria have also been found in pre-packaged salad. Researchers say that Shigella bacteria and many others may potentially survive in a MAP environment. Experts point out that both Clostridium and Listeria can potentially grow (slowly), even under standard refrigeration temperatures.

MAP foods have been linked to only a few foodborne illness outbreaks. In 2001, an outbreak of Salmonella Newport was linked to ready-to-eat salad vegetables in the United Kingdom. In 1990, a coleslaw mix was also linked to foodborne illness (botulism) in the US. In the perspective of the volume of MAP foods distributed, these incidences appear rare.

Sound Control Measures

In all, the most important practice for foodservice operators and consumers alike is to refrigerate MAP foods. Cold holding (41°F or below) throughout the supply chain is absolutely critical in maintaining the safety of these foods. Furthermore, realize that once a MAP package has been opened, it no longer provides a modified atmosphere, and the product will no longer enjoy extended protection from spoilage. Thus, it makes sense to keep MAP packages sealed until ready for use. Another control important for foodservice is date management. As with all food products, FIFO (first in, first out) and careful attention to "sell-by" or "use-by" dates is useful. With a MAP product, it's clear that any potential risk builds over time.

Finally, one good acronym deserves another: MAP requires attention to POTTWA, the factors that favor bacterial growth (potentially hazardous food, oxygen, time,temperature, water, and slight acidity). Here, think about the two T's: time and temperature. These basic controls go a long way with MAP foods.

MAP packaging provides convenience and extended storage. With that comes fewer shopping trips (or fewer deliveries for a foodservice department), and the labor advantages of pre-prep for many foods. Based on current evidence, MAP packaging is a sound choice.

By Sue Grossbauer