Active Packaging for Food Applications - Aaron L. Brody , Eugene R. Strupinsky , Lauri R kline

ACTIVE packaging, sometimes referred to as interactive or “smart” pack- aging, is intended to sense internal or external environmental change and to respond by changing its own properties or attributes and hence the internal package environment. Active packaging has been considered a component of the packaging discipline for several decades or since the first inclusion of des- iccants in dry product packages. In their own moisture-permeable sachets, desiccants absorb water vapor from the contained product and from the pack- age headspace, and absorb any water vapor that enters by permeation or trans- mission through the package structure. As separate entities within packages, active packaging sachets, pouches, patches, coupons, labels, etc., are not often integral to the package—a semantic differentiation.
Desiccant pouches are widely used in the packaging of hardware and metal goods. The best-known and most widely used active packaging technologies for foods today are those engineered to remove oxygen from the interior pack- age environment. Oxygen scavengers reduce oxidative effects in the contained product. Most oxygen scavengers in commercial use today are gas-permeable, flexible sachets containing reduced iron (i.e., iron not in the fully oxidized state) particles inserted into food and other packages from which air is initially removed by vacuum or by flushing with inert gas. During the last two decades of the twentieth century, commercial incorporation of oxygen-removal materi- als directly into a package structure occurred with varying results. Several ap- plications for beer and juice bottles became commercial in 2000.
The goal of active packaging, in conjunction with other food processing and packaging, is to enhance preservation of contained food and beverage products. For example, to optimize the effects of oxygen scavenging, oxygen should first be removed from the product during processing and packaging operations. The oxygen must also be thoroughly removed from the package

interior and the package materials, and the package structure, including mate- rials and closure, must be barriers to further oxygen entry. In other words, oxy- gen scavenging complements good oxygen-control practices.
In addition, oxygen is certainly not the only vector that can influence the quality of the contained food. For example, moisture gain or loss, light, non- oxidative reactions, microbiological growth, and enzymatic activity may all, individually or collectively, be involved in food-product deterioration.
Worldwide development efforts devoted to oxygen removal have indicated that analogous efforts by the same and parallel research teams continue to be applied to oxygen scavenging and are being studied for other active packag- ing forms. Michael Rooney’s book, Active Food Packaging (Rooney, 1995), coalesced some of the many known active packaging concepts for foods into a single volume. This book did not, however, probe deeply into some of the more promising technologies that have been proposed and have entered the marketplace, including antimicrobial films, carbon dioxide emitters, aroma emitters, and odor absorbers. Each of these is discussed or referred to in this text. On review of the commercial situation in the United States, and espe- cially the application of oxygen-scavenging compounds into the walls of beer bottles and processed-meat packages, the reasons for the notable paucities in the Rooney book become apparent. Although reviewed and referenced in commercial contexts, definitive scientific documentation and publications are lacking, unsubstantiated, or unclear. Descriptions of plastic bottle wall oxy- gen scavenging appear only in the patent literature, which does not, of course, detail specifics. The 1999 and 2000 George O. Schroeder conferences, “Oxy- gen Absorbers: 2000 and Beyond” and “Oxygen Absorbers: 2001 and Be- yond” (Anonymous, 1999, 2000) set out to probe the expanding realm of oxy- gen-removal mechanisms. The presentations offered excellent reviews of historical and contemporary technologies and scientific studies but did not elucidate on the intriguing, but still largely proprietary, industrial world of oxygen scavenging.
Nevertheless, many of the active packaging systems not fully discussed in the book Active Food Packaging have reached the commercial market, some with notable success. High-gas-permeability films, including some that increase their oxygen permeability with increasing temperature, are used for packaging fresh-cut produce. Use of these temperature-sensitive package materials is expected to increase because the technology developer has acquired a fresh- produce packager who, of course, uses the technology in its package materials.
Carbon dioxide and ethylene scavengers for modified-atmosphere (MA) or, more precisely, controlled-atmosphere (CA) food preservation are common in large bulk shipments. Carbon dioxide emitters to suppress microbiological growth have experienced limited success in modified-atmosphere packaging (MAP). Ethylene scavengers are among the more successful commercial ac- tive packaging technologies in the fresh-fruit bulk-shipment category.

Odors generated or captured within closed food packages are undesirable, and their obviation has been a research topic for years. Odor removers incor- porated into packaging are increasingly important in some classes of food packaging.
Antioxidants and oxygen interceptors incorporated into package materials, such as tocopherols (vitamin E), have emerged in recent years and are increas- ingly employed to combat odors generated in plastic processing. Tocopherols, which are nonvolatile, have not replaced volatile butylated hydroxyanisole/ butylated hydroxytoluene (BHA/BHT) which migrate into foods in product antioxidant applications, but they appear to be new antioxidants of choice for mitigating the effects of oxygen. Entities such as oxygen scavengers/intercep- tors react with oxygen to form new compounds. Oxygen absorbers may re- move oxygen by any means, including physical. Antioxidants react with free radicals and peroxides to retard or block the actual oxidation reactions. Se- questering agents tie up inorganic catalysts that might otherwise accelerate ad- verse oxidative reactions.
Members of the food technology and packaging communities have long re- garded package materials as an ideal reservoir and delivery vehicle for antimi- crobial compounds. For many years, sorbic acid has been incorporated spar- ingly on the interior of package structures as an antimycotic in a limited number of dry food packages. The obvious benefits of sorbic acid as a mold and yeast inhibitor have been one foundation by which numerous other an- timicrobial agents have found their way into food package materials. Unfortu- nately, most antimicrobial agents also exhibit toxicity when they enter the food from the package and would be consumed as part of the food. Thus, actual commercialization has been proceeding slowly, except in Japan where several compounds have been reported to function effectively as antimicrobials in commercial packages.
As with oxygen scavengers, the major technological and commercial suc- cesses for antimicrobials have been achieved by Japanese organizations for packaging Japanese products in Japan. Nevertheless, the concept of integrating microbistatic and microbicidal materials and plastic packaging has been very attractive. Numerous attempts have been and are being made to translate fa- vorable laboratory results into safe and effective commercial food packaging. The growing list of successes in active packaging beyond oxygen scavenging has been noted by the food-packaging community.


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