Action in Active and Intelligent Packaging

If 2001 was a banner year for publications on active packaging, 2002 promises much more. Packaging Strategies held its Active Pack 2002 conference earlier this month. BRGTownsendInc. will issue a multi-client study on active packaging by mid-spring. IFT’s Food Packaging Division has scheduled two symposia at IFT’s Annual Meeting in Anaheim, Calif., in June—one on antimicrobials and the other on active packaging. Campden Chorleywood Food and Drink Research Association will hold its second International Conference on Active and Intelligent Packaging in September. And active packaging will assuredly be featured at Interpack in Germany in April and Pack Expo in Chicago in October.

Will active and intelligent packaging percolate to a mainstream position, or will it be just a highly publicized packaging innovation that fades within a few years? With the 2001 growth of moisture controllers, ethylene absorbers, oxygen scavengers, theft deterrents, and analogous packaging adjuncts, we cannot but predict significant expansion, despite the challenge of justifying the increased costs.

• Moisture Controllers. These have reached far beyond the almost traditional silica gel desiccant pouches and cartridges that were, and still are, almost mandatory for electronic and metal product packaging. Purge absorbers that sort of control moisture content of the environment around packaged fresh produce and meat products prolong shelf life of cut tomatoes, melons, poultry, and probably a few other products. And researchers have demonstrated that inclusion of antimicrobials into the absorbers suppresses growth of microorganisms in the purge, otherwise a major initiator of product microbiological spoilage.

Perhaps the most intriguing moisture controllers are those in which the desiccants are incorporated into the package plastic itself. Blending the desiccant into the plastic structure separates the drying agent by polymer that is usually a moisture barrier, thus restricting the passage of free moisture to the absorber.

Apparently supported by a family of patents by Ihab Hekal on entrainment of desiccant in plastic, CSP Technologies, Auburn, Ala., has commercialized package structures capable of removing moisture from both closed and opened/reclosed packages. Microscopic interconnected transmitting channels are generated throughout the solid polymer structure of the package wall, especially at the inner surfaces. The channels provide pathways to permit diffusion of water molecules through the plastic structure so that they may be captured by the desiccant particles within the matrix. The plastic material with the active component can be physically bonded or co-injection, coextruded or coextrusion blow molded with other materials into multi-phase plastic package structures.

Physical proximity to structural plastics means that external plastic layers may function as moisture barriers while the interior structures are active moisture removers. The passive structures may be thermoplastics, such as moisture-barrier polyethylene or polypropylene. Agents such as polyethylene glycol produce the channels in the plastic surface on which desiccants such as silica gel, molecular sieves, or combinations, depending on the application, are situated.

The internally placed desiccants remove moisture from the atmosphere they contact and thus create what is in effect a dry atmosphere within the closed package. An interesting application is the physical insertion of a desiccant-laden interference fit sleeve on the interior of a cylindrical package such as a tubular vial. While sealed, the desiccant removes all residual moisture from the package interior and any of the small volume permeating through the plastic walls or transmitting through openings in the closure fitment/finish interface. Thus, dry product contents are protected against moisture damage during distribution. After opening and removal of part of the contents, the package is often reclosed. The active desiccant on the interior sleeve then can remove water vapor that has entered during the partial product removal step and return the interior environment to a dry state and thus retard the otherwise inevitable moisture damage.

Desiccant combinations may be engineered to the moisture-resistance requirements of virtually any dry product contents, limited only by the capacity of the desiccant that can be spread over the internal channels. Beyond semi-rigid bottle and vial materials as vehicles for this new technology is the realm of flexible packaging—thermoformable sheet and totally flexible materials have been produced with the desiccants in the structure. CSP has also combined the desiccant technology with controlled-release antimicrobials apparently activated by absorbed moisture. Effectiveness of this iteration has not been reported. The concept has generated more than speculation that the technology might reach into relative humidity control beyond just near-zero oxygen scavenging, e.g., odor removal, and controlled aroma release.

With reported technical success in retaining close-to-zero relative humidities in sealed packages, CSP may be on the brink of a wholly new universe of responsive packaging, all based on physical rather than chemical reaction principles.

• Oxygen Scavengers. Oxygen scavenging has grown mightily since it moved beyond the sachets of ferrous iron dropped into pouches of meat jerky for Japan and military rations of the late 1980s and early ’90s. The incorporation of non–iron-based oxygen removers directly into plastic package materials has propelled the notion of controlling food-deteriorative vectors through packaging as the food preservation medium. As a matter of fact, last decade’s coinjection stretch blow molding of polyester and nylon MXD6 has now been jumped (perhaps by reverting to original “elementary” 1980’s CMB Oxbar-type technology) by monolayer plastic structures from Amcor Polyester, Mississauga, Ontario, Canada.

Diene Types. Amosorb DFC (direct food contact; formerly Amoco Amosorb 3000) from BP Chemical is a polybutadiene/polyester oxygen scavenger engineered to blend with bottle-grade polyester to produce a monolayer, virtually zero-oxygen-permeation plastic. If applied in small but still effective concentrations, the blend remains transparent. Because the oxygen scavenging is initiated immediately after fabrication, logistics for empty bottles will be challenging. Such bottles, made by Amcor, have little carbon dioxide barrier and so are not (yet) suitable for carbonated beverages. Amcor has commercialized the structure for 16-oz plastic bottles for fruit beverages in the United States.

Nylon MXD6 Types. In contrast to the coinjection blow-molded nylon MXD6/polyester bottles, the Amcor structure appears able to resist elevated temperatures of hit-fill or post-fill pasteurization. As nearly as can be ascertained, the nylon MXD6 structures from Continental PET Technologies, Toledo, Ohio, cannot withstand beer pasteurization temperatures, while a recently developed Constar coinjection blow-molded nylon MXD6 structure could resist 140°F for 1 min.

Flavor Concerns. Little has been discussed openly of the adverse flavor results of oxygen reaction with most of the hydrocarbon dienes proposed as the active component of plastics for beverage bottles. DarEval, from EVAL Co. of America, Lisle, Ill., utilizes ethylene vinyl alcohol as a gas barrier and a polydiene oxygen scavenger and is reported to offer oxygen and carbon dioxide barrier with no discernible flavor difference from glass. Chevron Phillips, Houston, Tex., and Cryovac, Duncan, S.C., have combined to develop a flexible material containing benzo acrylate polymer characterized as free of any adverse flavors due to oxygen reaction. This material has reportedly been used as one layer of a lamination for heat-seal closure of moist pasta packages to maintain the oxygen at effectively zero and provide at least a 10-week refrigerated shelf life.

Ferrous Iron Technologies. Iron-based oxygen scavengers continue to grow. Among the striking examples are coextrusions for retorted can closures and retortable trays and rapid-acting sachets for zero-oxygen packaging of case-ready fresh red meat. Multisorb Desiccants, Buffalo, N.Y., supplies the case-ready-meat scavenger to Pactiv, Lake Forest, Ill., and Silgan, Norwalk, Conn., developed a multilayer closure containing ethylene vinyl alcohol oxygen barrier plus ferrous iron oxygen scavenger to spin-weld close bucket-type cans of children’s entrees. Mitsubishi Gas Chemical, New York, N.Y., offers sachets across the spectrum, and Ciba Specialty Chemicals, Tarrytown, N.Y., is active in ferrous iron for inclusion in package materials.

With about a dozen different oxygen scavenging systems in or near the commercial market, some confusion must prevail among users and, probably, regulators. With the paucity of data from suppliers or universities on application of oxygen scavengers, users have a much longer route to determine the inevitable practical applicability to packaging their products.

• Antimicrobials. A potpourri of data has been forthcoming from academia on antimicrobial additives for possible incorporation into package materials. Whether this plethora of data began with a target of controlling microorganisms in contained foods or as a complement for the seemingly ubiquitous edible packaging research cannot be stated for certain. Perhaps we might consider that oxygen scavengers are commercial and almost none of the antimicrobials are commercial in the U.S. despite years of research.

At the Active Pack 2002 conference, Cornell University’s Joe Hotchkiss summarized his published research:
Volatile Antimicrobials. The almost ubiquitous sachet has made it to both the commercial shelf in Japan and the university laboratory bench. Ethanol on carriers in sachets is evaporated in packages of soft bakery goods such as bagels to retard mold growth. Ethyl alcohol suffers from the residual flavor which (1) may be a natural constituent and/or (2) might be desirable to some consumers.

Other volatile antimicrobials such as chlorine dioxide (produced from its precursor in the package material by water vapor reaction) may produce adverse secondary effects on the food. Allyl-isothiocyanate produces a characteristic flavor that is generally undesirable.

Silver Salts. Silver salts on carrier materials such as zeolite are reportedly used in Japan, but not in North America because of efficacy and regulatory concerns. They function only when in contact with the microorganism—usually, but hardly universally, on the surface of the food—so functionality is questionable.

Coatings. An analogous situation occurs when the antimicrobial is incorporated into plastic materials—the majority of the active ingredient is below the plastic surface and cannot reach either the surface or the interior of the contained food. Coating of antimicrobials such as bacteriocins on package material surfaces has produced inconsistent results.

Hotchkiss noted that anhydrides of organic acids are much more effective than the free acid, which is relatively difficult to apply to package surfaces but which is the active form when activated from the anhydride by water vapor on the package surface.

Inherently Antimicrobial Plastics. Some polymers display inherent antimicrobial properties, such as chitosans and nylons whose surface amine concentration is increased by ultraviolet radiation activation.

The list of chemicals with claimed antimicrobial properties in package materials grows longer with each issue of peer-reviewed journals. As has been noted by IFT Food Packaging Division executive and Cryovac researcher Leslie Cook, a large gap exists between that which is reported in the literature and the realities of functionality in real package material structures. The gap is narrowing for some antimicrobials, but for too many, the differences between theory, laboratory bench, and commerce in some cases may be as great as infinite but in many situations may simply reflect the gap between narrowly focused research and reality.

Whereas not too long ago, active packaging could be neatly classified, the industry developments have evolved into a host of interacting technologies in which not just one benefit, but several, are achieved by systematic engineering of more than one active element. In the past, moisture was often required to activate active packaging for such things as oxygen removal. Tomorrow, we could be controlling internal relative humidity and oxygen, removing undesirable odors, and dispersing antimicrobials and desirable aromas into package interiors from a single package surface.

Meanwhile, the traditional food scientists and technologists continue to wrestle with food formulations, considering packaging only as an afterthought. Perhaps the time has arrived to consider welcoming active packaging into the mainstream of food science and technology.

By AARON L. BRODY
Contributing Editor
President and CEO, Packaging/Brody, Inc.
Duluth, Ga.