Convenience Food Packaging Today and Tomorrow: Solutions and Challenges
22.06.2007
Convenience is king with respect to consumers’ wants and needs from food packaging. Flexible packaging manufacturers have delivered, but today’s consumers demand even more from the films and pouches found on store shelves.
Foods never before considered in the convenience category are now widely available because of advances in packaging materials. Tasty, wholesome, even exotic prepared meals that can be cooked in their own packages, especially ones that can be eaten directly from the container, fly off store shelves. So do foods that don’t have to be refrigerated and that can go directly from shelf to microwave to plate. Tuna, which has historically been sold in cans, now comes in single-serve pouches. Salads, carrots, and celery sticks packaged in resealable bags occupy a significant portion of the produce aisle in supermarkets. Cookies and other treats are in reclosable zipper bags.
Foods never before considered in the convenience category are now widely available because of advances in packaging materials. Tasty, wholesome, even exotic prepared meals that can be cooked in their own packages, especially ones that can be eaten directly from the container, fly off store shelves. So do foods that don’t have to be refrigerated and that can go directly from shelf to microwave to plate. Tuna, which has historically been sold in cans, now comes in single-serve pouches. Salads, carrots, and celery sticks packaged in resealable bags occupy a significant portion of the produce aisle in supermarkets. Cookies and other treats are in reclosable zipper bags.
The common denominator—flexible packaging, manufactured with polypropylene, polyester, and nylon—has helped drive the explosive growth of convenience foods. But it has also placed increasing demands on the films used for making the packages—from barrier stability to sealabilty, to printability and sustainability. Fortunately, suppliers are driven to innovate by modifying existing packaging films to improve their properties and add value. But in some cases they are introducing entirely new films designed to meet specific requirements.
Retort Packages
Perhaps the fastest-growing area of flexible convenience food packages is retort pouches. This is driven in part by the rapidly rising cost of aluminum used for making cans, but also by the fact that retort pouches are lighter and, because they are flexible, can be packed more tightly than cylindrical cans, thus shipping costs can be reduced. They are also a brand manager’s dream because they can be gravure printed with bold, colorful graphics that make the package stand out on the shelf. They also provide a bigger “billboard” on a shelf than a can.
Equally important, however, is that they offer much better heat-transfer properties because they lay flatter than cylindrical aluminum cans. When food is retorted in a can, it takes longer for the food at the center to reach the proper temperature than it does for food near the walls of the can, which can be overcooked in the process. As a result, heating times can be shortened, heating costs can be reduced and, more importantly for the consumer, the quality of the food can be improved.
Films used for retort packages must meet the FDA’s requirements for retort applications and be stable at temperatures up to 125 degrees Celsius. They require high seal strength in order that they not burst while being heated. And they must exhibit excellent barrier properties for extended shelf life.
Common retort structures involve combinations of polyester and nylon films along with an FDA-compliant functional barrier layer. Retorting, however, is a very aggressive thermal process. As a result, oriented polypropylene is normally unsuitable for such applications, although cast polypropylene is often used for the inner sealant web.
The challenge facing suppliers is to develop stronger films with better barrier properties in order to minimize the number of layers required. This includes the development of barrier cast sealant films and barrier webs that are also printable. Notable developments in retort films include clear barrier vacuum deposition for oriented polyester films with excellent adhesion on both sides, high elongation oriented polyester to provide superior puncture resistance, and new metallized polyester with retortable adhesion, promoting layers to improve the bond between the metal and the base sheet.
Single-Serve Snack Packages
New single serve packages for more healthful snacking are being developed as a means of portion control in the face of a growing obesity problem. Popular new 100-calorie packages are a good example of that approach. Since such packages are commonly sold from P-O-P (point of purchase) displays, they must be attractive to consumers. Because their contents are commonly eaten on the go, however, they must also have good seals for durability and also be easy to open.
Excellent barrier properties are also required, especially for convenience foods in which trans fats have been replaced with other vegetable oils that are often less stable and more sensitive to oxidative rancidity. In fact, the problem is exacerbated by the fact that such products are typically sold in convenience stores, which tend to have a lower rate of turnover than supermarkets.
Films coated with aluminum or polyvinylidene chloride (PVdC) have traditionally been used for these applications. For clear film applications, PVdC-coated film, however, can be expensive, owing to its two-step manufacturing process. In applications requiring either a moisture- or oxygen- barrier property—but not both—its use can also lead to over-engineering. However, new, technologically-advanced co-extruded metallized and clear polypropylene films offering barrier properties approaching those of foil have recently been developed. These new polypropylene films have significant cost and performance advantages over traditional constructions.
Reclosable Snack Packages
Interestingly, packages that can be easily closed are also viewed as a means of portion control. It is thought that people are less likely to eat a significant portion of their contents if they can quickly reseal the packages to keep the food fresh. The manufacturers of several brands of cookies have adopted this approach with the use of zipper closures, and the trend is likely to continue. The important concern for the converter and the end user is to be sure that the film selected for the bag or pouch is compatible with the zipper material.
Fresh Cut Fruits and Vegetables
Pre-cut and pre-packaged salads are increasingly available in a number of varieties. Unlike packaging films for other perishable foods, film used for fresh cut fruits and vegetables must have a high oxygen transmission rate (O2R) to allow the food to breathe. At the same time, it must effectively seal out dust, microbes, and other foreign particles.
The film must also be sealable in a moist environment and should feel crisp, not soggy, to reinforce the impression that the food inside is really fresh. Thin gauge oriented polypropylene with a high O2R meets many of the foregoing requirements. The true challenge to suppliers is to create laminations that meet the different breath rates required by different vegetables.
Serve-In Containers
Dual-ovenable prepared dinners, especially low fat and low calorie varieties, have proliferated in recent years. They can be readied for serving quickly and, since they are packaged in rigid containers, no dishes need to be washed after they’re eaten.
The challenges for the film used for dual-ovenable lidding applications are that it must seal tightly but be easy to peel without delaminating or shredding, and it should not leave a sealant residue on the rim of the rigid container. Historically, polyester film made with a solvent coating has been used to create peelable lidding seals. However, solvents are problematic because they can migrate to the food and affect its flavor. Today, advancements in co-extruded polyester films made without solvents assure convenience food manufacturers that their customers experience a product that has a fresh, pure food flavor and comes in a cleanly sealed container that is easy to peel open and has no sealant residue on the rim of the container.
Environmental Challenges
It seems daily people hear or read something about “sustainable packaging.” Though industry and environmental leaders are still sorting out a formal definition, we do know that it is a multifaceted issue that encompasses a growing number of considerations—from source reduction to package design, to transportation costs and closed-loop recycling and composting systems.
Two specific environmental challenges face convenience food packaging: compostabilty and source reduction. Compostable plastic is a plastic that is capable of undergoing biological decomposition in an appropriate composting site, such that the plastic is not visually distinguishable and yields carbon dioxide (CO2), water, inorganic compounds and biomass at a rate consistent with other compostable materials and leaving no visible, distinguishable, or toxic residue. Polylactic acid (PLA), which is made from cornstarch, is a polymer that is fully compostable in municipal and industrial composting facilities. However, because of its low melting temperature, it is most commonly used for refrigerated food packaging and flower wraps.
The challenge facing flexible packaging film suppliers is to create films that are compostable yet exhibit the same properties as traditional oriented polypropylene or polyester. The greatest hurdle is barrier properties, followed by sealability and machinability. Currently suppliers use additives that are activated by the UV rays of the sun and allow film to eventually break down into smaller particles. But they do not fully decay. If the package ends up in a landfill, additives that require UV light are not effective. Thus research and development in these areas is necessary and ongoing.
Source reduction, a viable, practical approach to meeting environmental challenges, can be implemented today. According to the EPA, source reduction refers to any change in the design, manufacture, purchase, or use of materials or products, including packaging, to reduce their amount or toxicity before they become municipal solid waste.
Suppliers are currently working to achieve source reduction by down-gauging existing films, while maintaining barrier and machinability properties. Already there is success in this approach and further developments in improved barrier and machinability should be expected. Ultimately, source reduction through thinner films means less use of raw materials, innovative package design, reduced package weight and lower transportation costs.
Chris Voght is a strategic alliances manager at Toray Plastics (America), Inc.
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