Aaron L. Brody

The term “smart” packaging was coined about fifteen years ago to describe package structures that allegedly sensed changes in the internal or surrounding environment and altered some of their relevant properties in response. Simultaneously, academics and true researchers, concerned that the term was too juvenile, invented the term “interactive” packaging to describe the same entities and later shortened it to “active” packaging, the nomenclature employed today.

The problem with too much active packaging today is that it is not very intelligent, i.e., it does not really change with environment but rather functions in a less passive fashion than “ordinary” “barrier” packaging. The first of the true thinking packaging structures emerged about five years ago from a California research organization, Landec, with little knowledge, at the time, of what they had wrought and less of where they might use their intriguing concept. They found a wonderful outlet in seed coatings to delay sprouting until spring had certainly arrived. They are now applying it to minimally processed food packaging, although they had to acquire a food company to help persuade their potential food industry customers that they had an innovation that could really disturb conventional wisdom and benefit all.

Active packaging and modified atmosphere packaging are both important contributions to the retention of quality of foods after production, and as every food packaging professional asserts, packaging and distribution are indispensable elements of food preservation. Generally, packaging is passive, i.e., whatever attributes are built in by the integration of material, structure, equipment, and distribution are the totality of the functionality. When enumerating such properties, we are referring to water vapor, oxygen and aroma barrier, fat resistance, light barrier, aqueous liquid resistance, abrasion resistance, tensile strength, bond strength, heat sealability, hot tack, and so on. Occasionally, a technologist might take account of small changes in oxygen/ water vapor barrier properties with temperature increases or decreases, but this is relatively uncommon.

Parallel with, but far behind, passive packaging is what is called active packaging. Active packaging has attributes beyond the basic barrier. Included among these might be antimicrobial activity, desiccation and moisture control, aroma emitting, ethylene absorption, antioxidant emission, temperature control, temperature sensing, and visible indication. Regardless of the merits of any of these characteristics, and they are many, none involves actual sensing of an environmental situation, then triggering a response in the package material functionality.

The current technologies might be defined as slightly active because a few involve some action in the presence of the water from condensing water vapor—which is not an indicator of a need, so they are not quite passive. So, we shall shift quickly into the realm of modified atmosphere packaging, the other building block upon which rests the merits of the Landec research and development result.

Modified Atmosphere Packaging
Another of the technologies developed in industry and adopted by academics with the stipulation that its name be changed from the original “controlled atmosphere packaging” because true control was not effected, modified atmosphere packaging has led the evolution of fresh and minimally processed food preservation for the past two decades.

The term “controlled” implies that the entire internal package environment is precisely where the technologist prescribes it to be at any given time under any given external or internal situation. Control further implies that the exact environment optimizes the preservation effect of the internal gaseous atmosphere, as it often does. Those involved in retarding deterioration of fresh and minimally processed foods over long distribution certainly exercise control over the temperature, oxygen, carbon dioxide, water vapor, and ethylene concentrations by elaborate mechanisms in their storages, containers, and vehicles.

In modified atmosphere packaging, an initial atmosphere is generated by either permitting air to be enclosed or by injecting a desired initial gas mixture. This blend then changes as a result of multiple variables including:
• Respiration of the contained product which consumes oxygen and generates carbon dioxide and water vapor and, often, ethylene.

• Type, variety, cultivar, age and growing conditions of fruit or vegetable contents: although each type of product falls into a range, the range may be relatively broad for optimization of the internal environment.

• The natural aerobic and anaerobic microbiological load and its change with time and temperature.

• Respiration of indigent microorganisms which usually also consume oxygen and produce carbon dioxide and water vapor which, of course, changes with time, numbers, and temperature as well as internal gaseous environment.

• Permeation of oxygen, carbon dioxide, and water vapor through the package material.

• Transmission of oxygen, carbon dioxide, and water vapor through the seal and defective structural areas

•Temperature of the product which, as expected, causes increases in respiration rates.

• Temperature of the package material which may lead to small changes in permeation.

• Surface area of the package material.

• Thickness of the package material.

• Carbon dioxide to oxygen concentrations which may retard or accelerate product and/or microbiological respiration and which change with time and concentrations.

• Water form and concentration.

• Presence of other biochemical entities such as inherent natural antioxidants or antimicrobials.

• Light.

• And so forth.

Food packaging technologists are faced with a number of conflicting objectives in establishing their package specifications:
• Many fresh and minimally processed fruit and vegetables are benefited by respiratory retardation arising as a consequence of altered oxygen and carbon dioxide concentrations, with reduced oxygen and elevated carbon dioxide the most common variables.

• The respiratory retardation rates change with the changes in gas concentrations.

• An equilibrium oxygen/carbon dioxide ratio is often reached for any given temperature.

• Most fresh and minimally processed fruit and vegetables are subject to undesirable respiratory anaerobiosis that can lead to fermentative reactions and consequent off-flavors when the oxygen concentration drops to below certain levels.

• Pathogenic anaerobic microorganisms may grow under reduced oxygen environments, leading to possible adverse public health consequences.

• Commercial and developmental package materials generally are not offered with oxygen or carbon dioxide permeation rates that fit the singular needs of internal gas control within packages.

• The ratio of carbon dioxide to oxygen permeation of plastic package materials is generally fixed at a 3–5:1 level because of the polymeric nature of the material. This ratio generally limits the ability of natural respiration/permeation activity to achieve an optimum oxygen to carbon dioxide concentration within the closed package.

• Overt physical openings in the package material may reduce the propensity to respiratory anaerobiosis, but does not necessarily permit optimization and further allows the entry of microorganisms.

• Mineral filling of the polymer matrix is, in effect, the same as physical openings in the plastic film or sheet, with the exception that microorganisms generally do not enter.

• Water vapor should be retained to help preserve the product by retarding physical changes as well as biochemical deterioration, but which, in excess, can damage the product.

• Many marketing professionals want visibility of the contents, leading to a need for antifog and other agents to counter water vapor condensation on interior package material surfaces.

• Some of the available mechanisms to obviate fog interfere with package heat sealing.

• Surface to volume ratio of the package and package surface to product mass ratio are important.

• The time the product is expected to be in distribution is also important.

• The balance between quality retention is important, as well.

Modified Atmosphere Package Structures
Without belaboring a topic that has been discussed in great depth in trade publications, modified atmosphere packaging falls into two general categories: high gas permeability and low gas permeability.

Products that are regarded as non-respiring, such as pasta and prepared dishes, are generally packaged under reduced oxygen and so are in high-gas-barrier package structures. Respiring products such as fresh or precut produce are packaged in structures that have high gas permeability to reduce the probability of respiratory anaerobiosis.

Both categories are vulnerable to problems: the absence of oxygen in non-respiring  (and even respiring) product packages can lead to growth of pathogenic anaerobic microorganisms, and, in respiring product packages, to anaerobic respiration. For red meat products, the oxygen balance is more complex, since not only aerobic microbial growth is involved, but also myoglobin/oxymyoglobin/metmyoglobin interactions affecting the color.

Fresh and minimally processed produce packagers have addressed their perceived primary problem by employing package structures that have high gas permeability by virtue of their polymeric structure, gauge, surface to volume ratio or mineral or other fill. The rate of oxygen entering from the outside air depends on many variables, but essentially leads to a relatively narrow range of oxygen/carbon dioxide gas within the package at product equilibrium. And, if the temperature rises, the rate of increase in gas permeation through the package material does not match the rate of increase in respiratory gas consumption and production, leading to imbalances in the internal gas concentration and consequent sub-optimal atmospheric conditions and, more critical, anoxic conditions within the package. Further, of course, the ratio of carbon dioxide to oxygen permeation remains virtually fixed, so internal carbon dioxide content can increase to beyond desirable levels. This situation is especially bad with high-respiration-rate products such as broccoli, cauliflower and asparagus.

The employment of very-high-gas-transmission package materials such as mineral-filled and microperforated structures does not necessarily obviate the problem, since their properties do not change with temperature and the ratios of gas movement do not change at all.

Packaging technologists have a dilemma: their primary objective is to ensure product safety; their secondary objective is to maximize quality retention; but they are relegated today to addressing the now overriding issues of avoiding anaerobiosis, especially under the less than-ideal commercial distribution environment.

Landec and its Technology
Intellipac™ polymeric package materials, manufactured by Landec Corp., Menlo Park, Calif., are side-chain-crystallizable (SCC) polymers with the ability to effectively and reversibly melt as the temperature increases and thus foster increased gas transmission through them.

SCC polymers are acrylics with side-chains capable of effecting characteristics independently of the main chain. By varying the side-chain length, the melting point can be altered. By making the appropriate copolymers, it is possible to produce any melting point from 0 to 68° C., well within the extreme distribution temperature range of minimally processed foods.

SCC polymers are unique because of their sharp melting transition and the ease with which it is possible to produce melting points in a specific temperature range. When elevated to the switch temperature, SCC polymers become molten fluids which are inherently high in gas-permeability. The permeation properties may be modified by inclusion of other polymers to change the carbon dioxide to oxygen permeability ratios, for example. The resulting materials can permit the packaging technologist to achieve the lowest oxygen concentration without going anaerobic within the package. Thus, the optimum gas concentration may be employed from the outset of distribution with minimum concern for elevated temperatures.

In addition to the reversible temperature sensitivities, the materials are generally capable of 100 times greater oxygen permeability than mainstream polyethylene films without compromising the carbon dioxide to oxygen permeability ratio. This is accomplished by coating a porous substrate with a proprietary SCC polymer and applying the membrane as a package label over an aperture on an otherwise reasonably well-sealed package. Membranes with high carbon dioxide to oxygen ratio selectivity are best for products with carbon dioxide-sensitive contents to allow the carbon dioxide to escape at rate faster than oxygen can enter. Conversely, membranes with low ratios are more applicable to products in which high carbon dioxide values can inhibit microorganisms. Thus, the materials can be tailored to the exact requirements of the package contents.

According to the Landec marketing managers, their package materials are the only structures capable of satisfactorily containing high-respiratory-rate fresh and fresh-cut produce.

Despite their relatively high cost, Landec materials were commercialized during the 1990s and are being employed for many fresh produce items, where they are the package medium of choice. Look in your favorite club store to view pouches with patches (of Landec material) containing mixed cut vegetables or cut broccoli.

How far beyond these applications they proceed, especially now that Landec and a major produce supplier have joined forces, is a subject for business interests. How far beyond produce and into prepared foods vulnerable to pathogenic anaerobic growth the technology might penetrate is an issue that should soon be considered by interactions among Landec and food industry professionals, and the sooner the better.

The technology, which has emerged from industry sources, has been less than perfectly nurtured to date, but warrants very careful examination by many food and food packaging technologists who are struggling with the issues of food safety and quality retention for our burgeoning home meal replacement market. To be able to control the package structure to deliver controlled atmosphere within packages is a major accomplishment that truly deserves the name “smart packaging.”

Patents can be downloaded from www.uspto.gov and searched by keyword, patent number, or patentor.

High modulus oxygen-permeable multilayer film. U.S. patent 6,060,136, filed 7/7/1997, issued 5/9/2000 to R.E. Patrick, M.J. Walden, assigned to Cryovac, Inc. A multilayer film has a first outer layer, an inner layer, and a second outer layer. The first outer layer comprises a homogeneous ethylene/alpha-olefin copolymer. The inner layer comprises a thermoplastic elastomer. The second outer layer comprises a second ethylene/alpha-olefin copolymer. The inner layer is between the first outer layer and the second outer layer, and is chemically different from the first outer layer and the second outer layer. The multilayer film has an O2-transmission rate of from about 500 to 50,000 cc/m2 24hr STP, and a modulus of at least 60,000 psi. The multilayer film is especially useful for the packaging of O2-sensitive products, such as produce. The high modulus of the film enhances its performance in form-fill-and-seal operations.

Microwaveable bag having stand-up, wide mouth, features; and, method. U.S. patent 6,060,096, filed 4/14/1998, issued 5/9/2000 to D.E. Hanson and E.C. Jackson, assigned to Conagra, Inc. The microwavable bag can be used in constructions including a microwave popcorn charge therein. The preferred construction is folded from a single sheet, preferably a multi-ply construction having a microwave interactive arrangement positioned between the two plies. After popping, the arrangement forms a self-supporting bag with an open mouth for ease of access to popped popcorn.

Container for pourable food products. U.S. patent 6,059,153, filed 10/9/1998, issued 5/9/2000 to R.J. Olson et al., assigned to Kraft Foods, Inc. Describes a blow-molded polymeric container having an enlarged annular neck and a spout integrally molded on at least one side wall beneath the neck. The neck defines a mouth opening which is offset from a vertical axis in the direction of the spout.

Method and apparatus for forming and hermetically sealing slices of food items. U.S. patent 6,058,680, filed 12/29/1997, issued 5/9/2000 to V.A. Meli et al., assigned to Schreiber Foods, Inc. An apparatus and method are provided for forming a hermetically sealed package for a slice of a food item. A web of thermoplastic material is first formed into a tubular arrangement with a hermetic longitudinal seal. To form the tubular arrangement, means are provided for folding a continuous web of thermoplastic material into V-folded condition and for continuously forming a hermetic seal along the open longitudinal edge of the V-folded web. The hermetic seal is formed between the inner surfaces of the front and rear faces of the web to define a tubular web member. The food item which has been formed into a soft mass is then inserted into the tubular member and the tubular member is flattened to form a thin film tube. Means are provided for forming a hermetically sealed cross-seal; they are disposed substantially transverse to the longitudinal forward-moving direction of the web.

Products & Literature
Bottle Unscrambler Saves Labor.
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Molded seat for bottle filler. Clean-in-place features are essentials for automated milk-bottle filling machines. A new version of that part includes crush ribs that tightly lock the injection-molded seat to a molded rubber valve on the automated filler. The bond between the two materials prevents leaks and product contamination by avoiding the formation of a bacteria trap. The seats are molded of approved polysulfone material, an advanced thermoplastic that replaces the metal seats that are generally used. For more information, contact Minnesota Rubber QRM Plastics, 3630 Woodale Ave., Minneapolis, MN 55416, (phone 612-927-1400, fax 612-927-1470—or circle 322.

Contributing Editor

In This Article

  1. Food Processing & Packaging