MEATS, PRODUCE MAP OUT LONG SHELF LIFE

MODIFIED ATMOSPHERE PACKAGING HITS ITS STRIDE AMIDST CONSUMER DEMANDS FOR FRESH FRUITS, VEGETABLES AND READY MEALS AND CONCERNS OVER FOOD SAFETY.

By Mary Anne Falkman 

Although modified atmosphere packaging (MAP) has been around for about 40 years, it is only in the past 15 years that its momentum has swung decidedly upward.

Several socio-economic trends have fueled the growth. Consumer desires for fresh meats rather than frozen has spurred an increase in case-ready meats, while increasing use of microwave cooking has given rise to fresh, fully cooked ready-meals. But perhaps the most dramatic changes have occurred in the produce departments of supermarkets and club stores where fresh-cut produce with long shelf-life answers Americans’ desire to eat healthier foods that are optimally convenient to prepare and serve. 

Modified atmosphere packaging is a technique used for prolonging the shelf-life period of fresh or minimally processed foods, while eliminating or reducing the need for preservatives or chemical additives. Modifying the atmosphere around fresh foods is hardly a new concept. Controlled atmosphere storage (CAS) was used as long ago as the 1930s when ships transporting fruits used high levels of carbon dioxide in their holding rooms, thus increasing the shelf life of the product. Louis Pasteur had discovered the fact that removing oxygen slows the growth of aerobic bacteria. MAP can also be used to protect the sterility of medical devices and to prevent oxidation on industrial products, such as auto parts.

Oxygen absorbers are commonly used with electronics and medical devices, but they are not considered acceptable for food since the sachets introduce a foreign object into the package. However, the absorbers can be inserted between two layers of film, one highly permeable to oxygen and other a barrier, explains Ori Cohen, president of Orics Industries, College Park, N.Y. As a preservation technique, the air surrounding the food in the package is changed to another composition to prolong shelf life by slowing oxidation and natural deterioration. Meats need films of very low gas permeability so for such non-respiring products high barrier films can be used. The barrier will protect the initial vacuum or flushed gas-mixture. But fruits and vegetables are respiring products so the interaction of the packaging material with the product needs to be controlled.

Multivac R535 is the latest model for applications such as Mandar's diced fresh mango mentioned in the above sidebar. (It recently replaced the R530.)

If the permeability (for oxygen, carbon dioxide and moisture vapor) of the packaging film is adapted to the product’s respiration rate, an equilibrium-modified atmosphere will be established in the package, and the shelf life of the product will be extended.

The two primary techniques used to create a modified atmosphere for meat and produce are gas-flushing and vacuum creation, or a combination of the two. In gas-flushing the package is flushed with an inert gas mixture. For a vacuum pack, the air is removed totally; the package can be left that way or an inert gas can be inserted to replace the vacuum. All of these procedures are accomplished within the machinery, and then the package is sealed to protect its altered atmosphere.

The ORICS' SLTS is a straight line tray  sealing machine with the ability to run 30 to 120 trays per minute.

Cohen says the best control over the gas mix in a package comes with first pulling a vacuum, and then inserting the gas in the open environment. “That way, you can know exactly what the mix is,” he states.

The earth’s atmosphere consists of about 79 percent nitrogen, 21 percent oxygen and 0.38 percent carbon dioxide. It is the altered ratio of these gases that makes a difference in prolonging shelf life. By reducing the oxygen level and increasing the carbon dioxide level of produce, ripening of fruits and vegetables can be delayed, respiration and ethylene production rates can be reduced, softening can be retarded and various compositional changes associated with ripening can be slowed down. With fresh meats, a lowered oxygen level prolongs shelf life, but most red meats need some oxygen at retail in order to make the meat “bloom,” or turn  a bright red color.

Oxygen is present when packaging fresh fruits and vegetables as they continue to respire after harvesting. Because the total absence of oxygen can lead to anaerobic respiration in the package, which accelerates spoilage, some oxygen is desirable, but it needs to be controlled. When packaging meat, high carbon dioxide levels are effective bacterial and fungal growth inhibitors. In the case of vegetables and fruits, carbon dioxide is not a major factor. In cases where gas flushing is required, nitrogen is used as filler gas since it neither encourages nor discourages bacterial growth.

Recently, controversy has swirled over the use of carbon monoxide to gas flush red meats. Aaron Brody, president of Packaging/Brody, Duluth, Ga., says that the practice exists but it is still a subject of back-room gossip and speculation. Consumer advocates object to the use of carbon monoxide because it can keep red meat looking fresh and appetizing long after it has passed its expiration date, theoretically enticing retailers to keep the meat packages in the refrigerated case much longer than is safe. The American Meat Institute denies such allegations.

Produce packaging: Just breathe

“As soon as the produce is cut, it begins to die,” explains Jerry Welcome, executive vice president of United Fresh Produce Association. “But it is still alive. The packaging is critical to shelf life.” 

The first rule of thumb for gaining shelf life with fruits and vegetable is to keep the product clean, cold and minimally bruised, explains Myra Foster, new business development manager at Sealed Air’s Cryovac Food Packaging. Consequently, she says, any product which can detect and manage temperature control would be a plus. “The goal is to get the product from point A to point B with 12 to 14 days shelf life,” she explains. Foster sees more consumer convenience features on the horizon, like steam-in microwavable pouches for fresh produce. “The produce company can really differentiate its products through packaging,” she believes.

“Cut fruit is something of a challenge,” admits Foster. Too much moisture inside the package can cause microbial decay of the product, but some moisture is necessary. Unlike with fresh-cut vegetables and salads, she says, gas flushing is not needed. “There are mixed views on gas flushing,” she says. But a permeable material is a must since the fruit, like vegetables and salads, continues to respire.

Foster mentions the new Freshness Plus™ packaging as an example of how active packaging can extend shelf life.

The Freshness Plus family of products enables a focus on quality life through active packaging, not food formulation, including the prevention of mold growth, preservation of food color and scavenging of oxygen and confinement odors. The technologies are adaptable to a wide range of applications including fresh red meat, processed meats, bakery products and fresh pasta. Because Freshness Plus does not require iron-based sachets to scavenge oxygen, a foreign object is eliminated from the package. This active packaging can help deliver food with better flavor, aroma and appearance. “Active packaging technologies effectively reduce the need for food additives and preservatives without compromising a product’s shelf-life or freshness. They also create an opportunity for cleaner product labels,” explains Jim Mize, global vice president of new opportunities for Cryovac Food Packaging.

According to Jerry Hirsh, marketing manager at Multivac Inc., Kansas City, Mo., produce needs customized packaging for every product because each respires at its own individual rate. In some cases, the intent is to prevent too much oxygen from surrounding the product while allowing carbon dioxide and moisture vapor to move freely in and out. Perforating the film packaging allows this exchange of gases. The size and number of the perforations depends upon how much gas needs to be accommodated for each individual product. Multivac’s newest sealers perforate the film online just prior to packaging the produce, so special pre-perforated film is not needed. Any appropriate film can be used. The machine’s controls can be adjusted to customize the size and number of perforations.

Jim Belcher, director of marketing-case ready products for Sealed Air’s Cryovac Food Systems, says that about 40 percent of all fresh meat in retail cases is displayed in one of three formats. The preferred option is a rigid barrier tray overwrapped with shrinkable non-barrier lidding. The second most common method is a non-barrier tray and lidding packed three or four to a mother bag, or barrier pouch, which has been gas flushed to remove oxygen. When the trays are removed from the bag for retail display, the meat then blooms. The third option is barrier shrink film completely encasing a non-barrier tray.

Belcher explains that a vacuum pack with no oxygen would keep the meat freshest for the longest shelf life, but in the total absence of oxygen, red meat appears an unappetizing purple, and consumers have been slow to accept such an appearance. He says the Wegman’s supermarket chain (in New York state) has done well with vacuum-packed meats, as have organic and kosher grades of meats. “It’s a trust factor,” he explains. “The consumer needs to be educated.”

Both Belcher and Hirsh agree that currently, the perfect solution would be to package meats in a tray with two films, the bottom one non-barrier and the top, peelable film as a barrier. The barrier layer keeps the meat safe during transit but then the store peels off that layer and allows the meat to bloom to its red color in the retail case. “That’s the Holy Grail,” says Belcher. “It’s the ultimate goal, but it’s a tall order.”

Hirsh says that next on the horizon is the combination of modified atmosphere packaging with convenience features, such as reclosability. He says the technology currently exists to provide different atmospheres in different compartments of a portion pack, such as Lunchables. In that example, the compartment holding crackers could remain as is, but the compartment containing ham slices could be modified for lowered oxygen.

Both Hirsh and Belcher point to Cryovac’s new Darfresh® Bloom technology, designed to run on Multivac sealers, as a state of the art MAP technology.

The Cryovac Darfresh Bloom package brings vacuum and modified atmosphere packaging processes together in the same package to reap the benefits of both technologies.

Specifically designed for use with fresh red meat, this new case ready package prolongs shelf life and keeps red meat bright red. The package is comprised of three webs, starting with a rigid barrier bottom web that is formed online into a tray. Then, a permeable top vacuum skin web holds the meat close to the bottom web with a hermetic seal, while a top lidded barrier web maintains the gas mixture inside the package and provides a flat surface. Between the two top webs, a MAP compartment holds the gas mixture. The drip-proof, secure package is ideal for vertical display in the retail case and requires no absorbent pad thanks to the vacuum-skin technology. This package is formed online and is suited to run on the Multivac® RCD equipment range dedicated to the Darfresh concept.

While both the machinery and the material are critical to creating a modified atmosphere, seal integrity is paramount to maintaining that atmosphere for maximum shelf life.

“The seal integrity is one of the most crucial aspects of maintaining modified atmosphere, especially for food, pet food and pharmaceutical packaging when they are on the shelf for months, or even years,” says Marco Studer, head of sales and marketing at Rychiger AG, Steffisburg, Switzerland.

Processes such as hot fill, pasteurization and sterilization, as well as good packaging barrier materials, are the basis for a long and safe conservation of the product and thus for a long shelf life, Studer explains. To extend the shelf life further, Rychiger offers in-line vacuum and gas flushing systems to achieve residual oxygen levels below 0.5 percent for producing modified atmosphere packaging.

Rychiger was the first company in the world to commercially build filling and sealing machines for hot-fill and retortable products in the food, petfood and pharmaceutical industries. This was in the early 1960s, when the sealing window defined by the available materials and sealants was very narrow, and achieving highest seal integrity, combined with easy peelability, was a demanding challenge. The company’s approach of short dwell times, high pressure and low temperature results in high seal integrity and easy peelability.

The Cryovac Darfresh Bloom package brings vacuum and modified atmosphere packaging processes together in the same package. Multivac RCD equipment produces the three web package complete with a rigid barrier bottom, a permeable top vacuum skin and a MAP compartment.

“The last thing you want is to have your product shipped back to you,” says Studer.

An extremely strong and ultra-precise sealing station is the heart of Rychiger’s machines. The combination of a mechanical seal stroke and preloaded individual air-springs on every lane guarantees very precise and short dwell times at high seal forces. The temperature of each seal head is constantly monitored.

Rychiger’s primary filling and sealing machines are the FS 270, for small operations; FS Flexy 640, for medium production lines; and the FS 1100 for large capacity and high reliability.

Its primary heat sealing laboratory equipment is the Pilot R&D Sealer. Especially developed and designed for scientific and industrial research and development to exactly reproduce sealing parameters and characteristics, the sealer allows upscaling for use on industrial production machines.

While the technology exists to extend MAP to fresh seafood, it is not typically used in the U.S. at this time. There are currently no regulations governing modified atmosphere packaging for seafood, Cohen explains. “It’s like the wild west. In most cases, seafood companies are not using MAP,” he says.

Modified atmosphere packaging has been following consumer trends for the past several decades. The popularity of microwave ovens in the early 80s gave rise to ready meals, Cohen says. Then, in the late 80s and early 90s, consumers began to replace frozen foods and canned foods with high-quality fresh meals, with a resulting need to extend shelf life for these products. The demand for healthier foods and five-a-day servings of fruits and vegetables helped to spur the packaging of fresh-cut and cleaned produce in the early 90s, he says.

Orics’ latest machine is an example Cohen cites as state-of-the art for MAP.

The Orics’ SLTS is a straight line tray sealing machine and has the ability to run 30 to 120 trays per minute. Trays can run on any straight line conveyor system, either random or oriented, and the SLTS servo indexer will orient them to the correct center distance, pick them and place them in a single carrier for seal. Once the trays are in the carriers of the machine, the chamber will be locked with a servo drive toggle crank mechanism, a vacuum and/or gas flush seal and the cut of the film will take place. An inside cut of film trim can be achieved with no additional cost. Heat seal assembly configurations are available in five different chamber sizes. The SLTS is constructed from stainless steel to withstand a wash-down environment and meets or exceeds all FDA and USDA standards. 

“Modified atmosphere packaging is just one link in a chain for extending shelf life,” Cohen states. “The raw material has to be treated right, too. MAP can keep a good product good. But it can’t make a bad product good,” Cohen explains.

Looking to the future, Cohen says, “We will strive to develop exotic materials that are biodegradable and environmentally friendly. Perhaps we can get a high barrier film out of polylactic acid (PLA) or other natural materials.” Smart films and active materials, which can both sense and then alter the atmosphere inside a package, are also possibilities. The equipment of the immediate future will be fast, efficient and able to monitor the gas mixture inline for better control. “Materials will be very important and will be the key to good quality. But modified atmosphere requires the combination of material and machine,” he states.

Aaron Brody shares Cohen’s enthusiasm for the future of MAP. “This is much bigger than retort,” he says.  

Mary Ann Falkman is in her 15th year reporting on the packaging industry. She currently resides in Chicago, Ill.