With so much focus on the appearance of food packages, it's heartening to know that companies are putting as much energy into better protecting what goes inside.

PET bottles are spray-coated with PPG's Bairocade epoxy-amine coating as they move through the production line at Graham Packaging Co.'s York, Pa., plant. Exterior oxygen barriers are one way to make the material competitive with glass for oxygen-sensitive foods.
Air, Light and Water: not a failed R&B band but the enemies of processed food and drink as it moves from the plant to the consumer's table. It's the job of packaging to prevent oxygen, ultraviolet rays and moisture from contaminating those products, and new materials are coming on stream to better accomplish that mission.

Greater packaging functionality is being demanded by food companies, and suppliers are responding with materials that deliver it. Whether it's superior puncture resistance, improved light- or oxygen-blocking performance, or better moisture resistance, materials are ensuring that new and improved doesn't just refer to the package's graphics.

Film that provides a snug fit and impermeability is critical for meats and other products packed in modified atmosphere packaging. But even more is demanded of film used for fruits and vegetables, where "the packaging has to be a life support system," observes Devon Zagory, a food safety and quality specialist with Davis (Calif.) Fresh Technologies, consultants specializing in fresh-cut produce. With different produce respiring at different rates, the amount of oxygen entering and carbon dioxide exiting the package has to be customized to the produce in the bag and its mass, relative to the surface area of the package.

Perforations are one way to facilitate the flow of molecules in and out, and the smaller the holes, the better. Electrical discharge through the film can create micro-perforations; a more precise method is with lasers. Holes as small as 10 microns in diameter are invisible to the human eye, "but to a molecule of oxygen, they are huge," Zagory says.

Perforations are insufficient for highly respiring produce such as broccoli, cauliflower and asparagus. Fresh Express Farms and Apio Inc., two leaders in the $16 billion (including foodservice) fresh-cut produce market, are using breathable membranes that alter the molecular exchange rate depending on external temperature. The membranes are made from a proprietary polymer marketed by Landec Corp., which acquired Apio in December.

Prepackaged asparagus is Landec's latest innovation, which the firm hopes will replace the traditional packed-in-ice method of shipment. "There's less shrink from product drying out, and shippers don't have to use waxed cartons or moisture pads," according to Lynn Bodfish, Landec's director of sales and marketing. The firm also is focusing on international bulk shipments of fruits, a growing area that currently is dependent on air transit.

"Applying our temperature-switch technology to bulk shipments moving internationally could open up transport by ocean or by truck," Bodfish says. The Apio acquisition creates an opportunity to develop competencies in the fruit area. Potentially the most lucrative but also the most challenging produce to control, fresh-cut fruit remains a product in search of packaging that can preserve flavor and freshness beyond a few hundred miles' distribution.

This coating unit at Rexam's Greenfield, Ind., plant was modified to produce metallized paper.

PET seeks clear advantage

Another material with great upside potential is polyethylene terephthalate (PET). Thanks to better hot-fill performance, PET is capturing notable market share, mostly at the expense of glass. Attractive appearance is PET's advantage over other plastics, but greater functionality in terms of less oxygen penetration and greater heat resistance are needed.

"PET is clear, it's microwavable and marketing loves it," observes Theron Downes of Michigan State University's School of Packaging. "It has tremendous potential."

Before that potential can be realized, suppliers must come up with an affordable solution for oxygen-barrier protection.

"It's the Derby: We don't know which approach will win," says Lindsay Mulholland, R&D manager at Amcor PET Technologies in Mississauga, Ont. "Several of the technologies meet the technical requirements. The next question is, can we do it economically? Then there is the environmental aspect; we have to pass that screen."

While Amcore has not settled on which oxygen barrier approach to pursue, Mulholland believes recyclability favors coatings on the outside of the container. Stripping those coatings off is relatively easy and yields better stock for recycling, he says.

The leading exterior coating on the market is PPG's Bairocade. York, Pa.-based Graham Packaging Co. is applying Bairocade to some of its client's PET containers, though the firm also is pursuing multilayer compositions, according to John Denner, director of PET packaging development. "Exterior coating is a proven technology, and it allowed us to enter the super-barrier packaging segment quickly," he says. Multilayer solutions are bogged down by legal entanglements, and packaging suppliers face pressure to offer PET solutions now to segments rapidly converting to PET, such as the single-serve juice category.

Fabrication lines are being upgraded. When production began last summer on Welch's jelly jars, vacuum panels were engineered into the top of the container to spell out the brand name in bas-relief. Unfortunately, a corresponding indentation on the inside made it difficult to scrape out the jelly. The indent has since been smoothed out.

Ragu recently began hot-filling its pasta sauce into blow-molded PET jars, taking advantage of the plastic's ability to handle temperatures up to 205 degrees F before objectionable shrink occurs. On the horizon are containers that can be retorted at 260 degrees for 30 minutes. That would make PET appropriate for baby foods and soups with meat.

"Polypropylene is another plastic that seems to have retort applications, and the material cost is less than PET," Denner says. "But it's not as clear and can't be blown as rapidly as a PET jar, so the manufacturing cost is a problem."

Raising the retort threshold another 50 degrees would open up a wide range of low-acid foods for PET, agrees Amcore's Mulholland. "We're trying to push the envelope on temperature," which would make PET more attractive to products such as single-serve dairy drinks. Teens and young adults are gulping down Nesquick milk in clear PET. "With the success of Nesquick, companies got the message that these products have to be treated as a beverage, not a dairy product," Mulholland says.

Higher heat tolerance and better oxygen barriers could lead to PET's holy grail: beer bottles. Miller Brewing is testing PET for beer, which accounts for a big chunk of the 8 billion glass containers sold each year in the U.S. But glass is still superior at protecting oxygen-sensitive beer, although PET may be better at blocking light. "We can definitely match amber glass as a UV barrier," says Mulholland.

Temperature-sensitive membranes on bulk packages of fresh-cut vegetables alter oxygen/carbon dioxide exchange rates, depending on ambient temperature and product mass. The membranes may be modified to control more complex respiration rates in cut fruits.

Better-tasting milk

UV's impact on beer's taste long has been recognized, which is why most brewers prefer brown bottles. Retailers now are recognizing the negative impact of light on the taste of milk, an effect that becomes more common as the code dates are extended because of greater thermal treatment. Kroger, Winn-Dixie and other grocers are shifting to darkened dairy coolers to reduce flavor degradation.

Off tastes weren't an issue in the 1960s, when gable-top containers dominated the milk market. While the rest of the country accepted the shift to high density polyethylene (HDPE) containers, consumers in the Pacific Northwest opted for flavor over convenient pouring. That region remains as milk's last gable-top stronghold.

"All new Kroger stores built in the last nine months have front-sliding racks that keep the milk dark," points out Clair L. Hicks, a food scientist and packaging specialist at the University of Kentucky. "If a container is placed two inches from a light bulb, you can get an off taste in one hour."

Stores in rural areas are unlikely to be retrofitted with darkened coolers any time soon. To cater to those customers' taste buds, two more Kentucky dairies recently switched to HDPE containers that are opaque, rather than translucent. Opacity adds cost, but consumers are embracing opaque bottles.

Suppliers like Rexam Inc. are developing metallized paper wraps to meet food manufacturers' demands for function as well as form.
"Consumers like to see the level of milk in the container so they'll know when they're running low," believes Martin Shearer, president of Southern Belle Dairy Co. in Somerset Ky., which uses translucent HDPE bottles. Still, the pigmented bottles from Dean Foods in Louisville and Flav-O-Rich Dairy in London, Ky., are proving popular. "We're not in a hurry to change, but we will be revisiting the issue and doing more focus groups," concludes Shearer.

While Dean Foods is confident its milk isn't leaving stores with an off flavor, "you want to extend that freshness beyond the store," explains Lew Niseo, vice president of strategy.

UV's impact on milk flavor and vitamin degradation is a contentious point. Before introducing a vitamin C-fortified milk, Boston's H.P Hood Dairy commissioned a Cornell University study to "prove us wrong" that light had no impact, a dairy spokesman recalls. Instead, the study strongly suggested light degrades the product.

Enhanced nutrition undoubtedly drove most of the new product's success, but the white pigmented bottle didn't hurt. Bottom line: white milk sales for the dairy are up 65 percent since the October 1997 launch.

Metallized film and paper are representative of packaging's glamour segment, but as they migrate into more food applications, suppliers are adding more functionality. The material's appearance helps move product. But food companies want more than just a pretty face.

Rexam Inc. is developing new metallized papers with barrier properties. Trials were scheduled last month using chocolate products to demonstrate the material's effectiveness as a grease barrier.

"Metallized paper has never had barrier properties before, and this is significant in gaining a foothold in food and beverage," notes Mark T. McGarel, Rexam's sales vice president.

For moisture-sensitive products, food companies increasingly are opting for metallized films, such as oriented polypropylene film. "Anything that is moisture-sensitive is a candidate for OPP," according to Chris Lockhart, marketing manager of Toray Plastics (America) Inc.

The raw material common to most of these packaging materials is plastic. After the early-1970s Arab oil embargo, doomsayers predicted plastic's presence in food packaging would decline; instead, it is pervasive. But as price spikes recently reminded motorists, petroleum costs can be volatile, and there is no guarantee plastic's raw material costs will continue to trail inflation.

"The official line is that resin costs are tied to more stable prices than oil; on the other hand, if you triple the price of oil, can the cost of making plastics-based packaging really be insensitive?" muses Amcore's Mulholland. PET's emergence in the food industry coincided with the Asian economic collapse. As the rice tiger begins to stir, the supply and demand for petroleum begins to shift.

That could pave the way for food-based polymers (see opposite page). Or it could signal a switch to nonplastic materials, such as metallized paper. In any case, food companies will demand materials that meet their functional needs.

Three approaches are being pursued:

  • coatings on the outside of the container
  • coatings on the inside of the container
  • multilayer fabrications with active or passive oxygen inhibitors.

Australian researchers believe rigid plastic packaging can be replaced with new plastics made from wheat starch.

Sidebar: Tree huggers, rejoice: food-based packaging increases

With everything from wheat starch to corn sugar being developed to create packaging for foods and beverages, industry is beginning to win grudging praise from even its harshest critics in the environmental camp.

Ground was broken last month for a $300 million Blair, Neb., plant that will annually produce up to 140,000 metric tons of thermal plastic resins made from natural sugars found in corn and other plants. The plant is being built by Cargill Dow Polymers.

Cargill Dow calls its new family of polymers NatureWorks PLA (polylactide polymer). French yogurt marketer Danone is among the first to use the new resins, which can be processed on conventional injection-molding equipment and biodegrades in the same time as paper.

"Biodegradability is important with food packaging, since recycling often isn't an option," points out Bill Sheehan, coordinator of the Grassroots Recycling Network. The group recently took on Coca-Cola for misleading recycling claims, winning a pledge from the soft drink firm to include 10 percent recycled content in its PET packaging.

Researchers at Australia's Cooperative Research Centers enjoyed a strong response when they recently debuted a similar alternative to petroleum-based polymers at Germany's Hannover Fair. "The materials consist of wheat starch and are blended with other biodegradable materials so they will compost down fully in around 30 to 60 days," says Roger Edwards, the centers' executive director. He expects the material to replace 60,000 tons a year of polystyrene trays, vegetable bags and other packaging.