ACTIVE PACKAGING - ANTIOXIDANT CAPACITY
Introduction
Our lunches are more often eaten “on the run” and quite a number of full time workers choose not to leave their desks for lunch at all. Younger people generally rely on take-home or on-the-go meal solutions. And many, if not most, of the consumers prefer conveniently packaged food that can be quickly made into meals without sacrificing the food’s quality. One observes an increasing demand for microwavable products, zippered pouches and ready-to-eat salad kits. Moreover, consumers expect to be informed about the origin, processing, properties and safety of the packed food. Food and beverage packagings have conceptually been defined as passive barriers that delay the adverse effects of the environment on the packed food products. Today, it is obvious that optimal passive packaging solutions result in initial quality and shelf life that are below the ones considered desirable. Their status quo is challenged by active packaging systems. Active packaging has been variously classified in the literature by a number of differing definitions [Rooney 1995; Day 2003; Robertson 2006]. Obviously, intensive research efforts to develop packaging materials that interact actively with their environment and/or with the packed food have resulted in an explosive growth of active as well as Avtive Packaging - Antioxidant Capacity
intelligent packaging systems. They are designed to prolong the shelf life of the packed food items and beverages as well as to improve their safety and organoleptic properties. Food contact materials can e.g. serve as matrices from which active ingredients are delivered into the products. Releases of antimicrobial agents, flavorings or aromas and antioxidants are common examples. On the other hand, many absorbing systems are used to decrease or control oxygen, ethylene, moisture as well as unwelcome odors or tastes.
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Oxygen removal
The quality and shelf life of packed food products are known to be decreased by the influence of oxygen. Food is highly susceptible to oxidative damages : oxygen can have considerable detrimental effects on the food. Consumers are worried about discolorations (e.g. oxidation of plant pigments such as chlorophyll and carotenoids or meat oxidation), off-flavors (e.g. pronounced rancidity as a result of lipid oxidation), nutrient losses (e.g. trough oxidation of vitamins) or accelerated aerobic microbial growth in meat, prepared dishes and other food items [de Kruijf et al. 2002]. Even very small amounts of oxygen, i.e. in the range of 1 to 200 ppm (or mg of oxygen per kg of food) may cause a substantial quality loss. The levels of residual oxygen in most packaging systems are much higher, e.g. between 0.1 % in vacuum packs and 2 % in gas flushed packaging processes. Therefore, avoiding access of oxygen to the filled goods as well as decreasing the levels already present at the time of packing are both priority objectives in food packaging. Important access routes for oxygen to filled goods are the inherent permeability of the packaging materials and artifacts in the final package. Sometimes, suitable materials combine passive with active barrier layers, e.g. oxygen consuming layers or oxygen scavengers. At present, several methods for the incorporation of oxygen scavengers into the packaging are known. Mostly separate elements such as sachets or tablets are used. Since these methods are not always compliant with the legislation of the countries, new concepts for better barrier properties are required [Amberg-Schwab 2004]. Current research efforts and developments focus on the advantages of Avtive Packaging - Antioxidant Capacity
homogeneously incorporated oxygen scavengers in packaging films. In general, existing oxygen scavenging technologies utilize one of the following mechanisms : iron powder oxidation, ascorbic acid oxidation, photosensitive dye oxidation, enzymatic oxidation (e.g. glucose oxidase/catalase and alcohol oxidase), ferrous salts or unsaturated fatty acids (e.g. oleic and linoleic acids). Exceptionally combinations of those are used. Overall, the oxygen absorption technology uses chemical reactions with reagents characterized by their high affinity for oxygen. A majority of the presently available
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oxygen scavengers is based on the reaction of iron with oxygen. The principle behind this oxygen absorption is rust formation. To prevent the iron powder from imparting color to the food, the iron is contained in sachets. The sachet material is highly permeable to oxygen and water vapor. As a rule of thumb it is generally accepted that 1 g of iron reacts with 300 mL of oxygen. A self reacting type contains moisture in the sachet and as soon as the iron is exposed to air the reaction starts. Oxygen scavengers can be applied as sachets containing oxygen absorbing components, which are inserted into the package or are adhesive bonded to the inner wall of the package. Occasionally they can be incorporated in the closure or in the packaging material through dissolution or dispersion into the plastic material or immobilization of oxidizing enzymes in the packaging material. The popularity of oxygen scavenging polyethylene terephthalate bottles, bottle caps and crowns for beers and other beverages has significantly increased [Anon. 2005]. The main advantage of these absorbers is their capacity to reduce the oxygen levels to below 0.01%, which is substantially lower than the levels typically found in conventional systems. In order to obtain even greater absorbing effectiveness, optimal conditions must be met, such as a very low oxygen permeability rate (typically <20 cm3/m2.atm.day) and perfect sealability. Additionally, the humidity of the food, the amount of oxygen dissolved, the amount of oxygen initially present and the free air flow around the sachet must be taken into consideration [Cruz et al. 2006]. Non-metallic oxygen scavengers have been developed to alleviate the problematic potential of metallic taints being imparted to the food products. Several other synthetic and natural chemicals are used in oxygen scavenging applications. Literature reports highlight the application of sulfites, boron, palladium catalysts, glycols, Avtive Packaging - Antioxidant Capacity
unsaturated fatty acids such as oleic, linoleic or linolenic acid and hydrocarbons. They also refer to enzymatic oxygen scavenger systems using either glucose oxidase or ethanol oxidase, which could be incorporated into sachets, adhesive labels or immobilised onto packaging film surfaces [Brody et al. 2001; Day, 2003]. Whereas the absorbing systems eliminate the oxygen by “magnetizing” it towards reagents, releasing systems “channel” reagents into their immediate environment. Hereto, one or more chemicals migrate off the packaging. One enters into the heart of the active packaging systems’ realm here; the food industry became highly interested
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in polymer packagings serving as reservoirs or matrices from which active ingredients are delivered in a controlled manner into the packed product. As early as the eighties, additives such as BHA or butylhydroxyanisole and BHT or butylhydroxytoluene were incorporated into wax liners for the cereal industry [Labuza et al. 1989]. The additives were released from the liner by diffusion into the cereal flakes to protect the food from lipid oxidation. The release of BHT from an antioxidant active packaging consisting of coextruded films made of low density polyethylene (LDPE), enriched with 8 mg/g of the antioxidant in the LDPE layer, complies with the legal limit established for food products [Soto-Cantú et al. 2008]. Our interest in antioxidant packaging has been stimulated by two influences. Originally, consumers demanded for reduced antioxidants’ (and other additives ‘) levels in the food. Moreover, today’s consumers are increasingly concerned with the use of synthetic chemicals and believe that natural antioxidants are safer and have a greater nutritional benefit. One is well aware that the human aging process can be accelerated by oxygen, and many doctors recommend we consume food rich in antioxidants, such as fruits, fresh produce, wines and vitamins. Nature does an excellent job in controlling the degradation process by maintaining high levels of antioxidants. The observation that fruits, vegetables as well as whole grains, as part of an overall healthful diet, have a potential to delay the onset of many age related diseases triggered a continuing research aimed at identifying their antioxidant agents. Antioxidants are present in foods e.g. as vitamins, minerals, carotenoids, and polyphenols. Many of them are identified in food by their distinctive colors : the deep red of cherries and of tomatoes, the orange of carrots, the yellow of corn and saffron Avtive Packaging - Antioxidant Capacity
and the blue-purple of blueberries and grapes. The most well-known food antioxidants are vitamins A, C, and E; β-carotene; selenium and lycopene. The International Food Information Council [http://www.ific.org] provides excellent comprehensive listings of functional food components. Since the major role of food packaging is to retard the natural processes that lead to food spoilage, antioxidants and free radical scavengers are used for this purpose. The stabilization of beef meat is exemplary for antioxidants’ applications. The meat surface discoloration largely depends on the oxidation rate of the red oxymyoglobin into metmyoglobin. Net accumulation of metmyoglobin occurs when meat ages, leading to its unattractive brown color. This browning generally proceeds in parallel
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with fat oxidation (enhanced rancidity) and is affected by temperature, relative humidity and oxygen partial pressure. Traditional food producers resolved the oxidation reaction by addition of synthetic antioxidants. Although intensively applied for meat derivatives, the addition of synthetic additives to fresh meat is not permitted. Therefore, a preferable option is the use of natural antioxidants. Recent studies [Nerin et al. 2006; Bentayeb et al. 2007] describe a new active packaging consisting of a polypropylene (PP) film in which a rosemary extract containing natural antioxidants is immobilized. The results showed that, compared to normal polypropylene, the active film containing natural antioxidants efficiently enhanced the stability of both myoglobin and fresh meat against oxidation processes. The authors consider it a promising way to extend the shelf life of fresh meat. The EC funded Quality of Life ACOSIC [http://www.acosic.com/html/project.html] project investigated novel oxygen scavenger systems as well as oxygen indicator systems and tested them with respect to their applicability in multilayer films for flexible packaging. It goes without saying that other new developments and applications are to be expected in the future. Moreover, among the oxygen reduction advances in packaging have been the introduction of polyvinylidene chloride (PVDC) coated films, incorporation of polyvinyl alcohol (PVOH) as an oxygen barrier layer, and the use of vacuum deposited aluminum to reduce oxygen penetration to packaging products. Also, vacuum packaging and use of inert atmosphere significantly extend the shelf life of many food products.
Avtive Packaging - Antioxidant Capacity
Additionally, consistent levels of antioxidants in food might be achieved by the controlled release of antioxidants from biodegradable plastic films, such as polylactide (PLA), polyglycolide (PGA), and the copolymers such as poly(lactide-co-glycolide) or PLGA. These polymers are widely used in the biomedical field for sustained release preparations, e.g. narcotic antagonists, fertility controlling agents, anticancer agents, local anesthetics, antibiotics and vaccines [Cheng et al., 1998]. The diffusion controlled release of BHA and BHT from food package liners into dry food products, such as cereal, has been studied earlier [Labuza et al. 1989; Miltz et al., 1995]. Now there is firm evidence for the potential use of biodegradable polymers as unique active packaging options for sustained delivery of antioxidants to dairy
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products. When adding Îą-tocopherol and ascorbic acid to milk, light induced oxidation off-flavor was significantly reduced in comparison to unspiked milk. Otherwise, Îątocopherol, BHA, and BHT migrated into whole milk powder through diffusion over four weeks of storage at 25 C, and tremendously reduced the production of light
Avtive Packaging - Antioxidant Capacity
induced oxidation compounds [van Aardt, 2008].
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References
Amberg-Schwab [2004]. Inorganic-organic polymers with barruer properties against water vapor, oxygen and migrating monomers; in Handbook of Sol-Gel Science, Volume 3, Chapter 36 Anon. [2005]. Up and active – Pira’s latest market report plots a healthy future for active packaging, Active & Intelligent Pack News 3, 25, 5. Bentayeb et al. [2007]. Direct determination of carnosic acid in a new active packaging based on natural extract of rosemary; Analytical and Bioanalytical Chemistry 389, 6, 1989 Brody et al. [2001]. Active Packaging for Food Applications, CRC Press, pp. 218 Cheng et al. [1998]. A poly(D,L- lactide-co-glycolide) microsphere depot system for delivery of haloperidol; Journal of Controlled Release 55, 203. Cruz et al. [2006]. Efficiency of Oxygen – Absorbing sachets in different relative humiditries and temperatures; Ciência e Agrotecnologia 31, 6, 1800 Day [2003]. Active packaging; in Food Packaging Technologies (eds. Coles et al.), CRC Press, Boca Raton, FL, USA, pp. 282–302 De Kruijf et al. [2002]. Active and intelligent packaging: applications and regulatory aspects; Food Additives and Contaminants 19, 144 Labuza & Breene [1989]. Applications of active packaging for improvement of shelf-life and nutritional quality of fresh and extended shelf-life foods; Journal of Food Processing and Preservation 13, 1 Miltz et al. [1995]. Trends and application of active packaging systems, in Foods and Packaging Materials – Chemical Interactions (eds. Ackermann et al.), The Royal Society of Chemistry, Cambridge, England.
Avtive Packaging - Antioxidant Capacity
Nerin et al. [2006]. Stabilization of Beef Meat by a New Active Packaging Containing Natural Antioxidants; Journal of Agricultural and Food Chemistry 54, 7840 Robertson [2006]. Food Packaging – Principles and Practice, second edition, CRC Press, Boca Raton, FL, USA Rooney [1995]. Introduction to active food packaging technologies; in Innovations in Food Packaging (ed. Han), Elsevier Ltd., London, UK, pp. 63–69 Soto-Cantú et al. [2008]. Release of Butylated Hydroxytoluene from an Active Film Packaging to Asadero Cheese and Its Effect on Oxidation and Odor Stability; Journal of Dairy Science 91, 11 Van Aardt [2003]. Controlled Release of Antioxidants via Biodegradable Polymer Films into Milk and Dry Milk Products, PhD Virginia Polytechnic Institute, pp. 173
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