Packaging and Shelf Life of Produce

Packaging and Shelf Life of Produce

Packaging and Shelf Life of Produce L Angiolillo, A Conte, and MA Del Nobile, Food and Environment, University of Foggia, Foggia, Italy Ó 2016 Elsevie...

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Packaging and Shelf Life of Produce L Angiolillo, A Conte, and MA Del Nobile, Food and Environment, University of Foggia, Foggia, Italy Ó 2016 Elsevier Inc. All rights reserved.

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Introduction Barrier Properties Active Packaging Intelligent Packaging Future Trends References

Introduction The increased consumer awareness toward food safety and quality issues and the greater time that food takes to reach the final consumer has led the food industry to pay attention on development of effective scientific and commercial strategies for ensuring a food product able to keep as long as possible quality and safety. Product shelf life is defined as the period of time during which the quality of packaged food remains acceptable. This period may range from few days to over a year, depending on the product’s characteristics, processing, packaging, and storage conditions. Nowadays the role of food packaging has become more and more relevant because it should not only contain a food product, making easier transport and storage, but its primary function should be directed toward microbiological, chemical, and sensorial protection of food items. Undesirable quality changes that take place during storage may affect texture, flavor, color, overall appearance, nutritive value, and safety of food (Petersen et al., 1999). However, the rate and the entity of many of these quality changes can be minimized with suitable food packaging systems designed to counteract the main extrinsic deteriorative factors such as moisture, oxygen, light, temperature, and aroma transfer. In order to choose a package capable to increase product shelf life, the first step is to achieve a deep knowledge of product characteristics, such as food’s moisture and susceptibility to oxygen. The second step to choose the right packaging system requires a deep knowledge of the material and the type of protection to be applied (Mastromatteo et al., 2011). Generally speaking, packaging performances can be grouped into mechanical, thermal, optical, and mass transport properties, but the extent to which a packaging acts to preserve a food largely depends on its barrier properties (Del Nobile and Conte, 2013). A chemical protection is guaranteed through a package capable of lowering enzymatic reactions determined by temperature, water activity and oxygen, lipid hydrolysis, lipid oxidation, protein denaturation, and hydrolysis. In other cases a package has to ensure a physical protection against softening, toughening, loss of solubility, loss of water-holding capacity, wetting, caking, agglomeration, or emulsion stability. For specific fresh produce, a package should maintain ideal conditions to control senescence (ripening or aging) or to prevent microbial deterioration by means of its capability of maintaining an ideal internal environment. Also in these cases the proper selection of film mass transport properties is of crucial importance. Recently, packaging systems have been designed to perform some specific interactions rather than providing only an inert barrier between the product and the surrounding. The active interaction with the food product ensures food quality maintenance or improvement. Packaging is used to monitor and communicate to consumer the conditions of the packaged food, providing information about the quality during transport and distribution on the shelf (Otles and Yalcin, 2008). This article will describe the most relevant aspects of the food packaging systems in relation to their influence on produce shelf life. In particular, the importance of barrier properties of passive polymeric systems, the effectiveness of active packaging, and the functionality of intelligent solutions will be discussed.

Barrier Properties The proper selection of packaging materials allows maintaining product quality and freshness during distribution and storage. Materials traditionally used in food packaging include glass, metal (aluminum, foils and laminates, tinplate, and tin-free steel), paper, and plastic. Moreover, a wide range of innovative plastics has been introduced in both rigid and flexible forms. Today’s food packages often combine several materials to exploit each material’s functional or aesthetic properties. Table 1 describes the most common materials used in food sector with their main advantages and disadvantages. The most common quality losses are due to mass transport properties of plastic packages (Tihminlioglu et al., 2010). Permeation consists in molecules diffusion through the package wall and a subsequent absorption or desorption from/into the internal/external atmosphere. The selection of the best packaging material is crucial in the food sector because the package needs to be enough versatile to withstand handling process forces maintaining physical and chemical integrity and it also must ensure good barrier properties to several gases, above all, when modified atmosphere conditions are adopted (Galotto et al., 2008). A packaged food can be considered as an interactive system in which an exchange of mass and energy between the food, the packaging material, and the external environment takes place. These interactions may affect both food and package. The final attributes of a packaging material, especially in terms of barrier

Reference Module in Food Sciences

http://dx.doi.org/10.1016/B978-0-08-100596-5.03220-0

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Table 1

Properties of food packaging materials

Material

Advantages

Disadvantages

Food application

Glass

l

l

l

l l l l l

Aluminum

l l l l l l l

Polyvinylidene (PVdC)

l l l

Polyvinyl chloride (PVC)

l l l

Low-density polyethylene (LDPE)

l l l l l l

High-density polyethylene (HDPE)

l l l l l l

Polyvinyl alcohol (PVOH)

l l

Polyethylene terephthalate (PET)

l l

l l

Polypropylene (PP)

l l l

Impermeable to gas and water Chemically inert Resistant to heat process Transparent Odorless Recyclable Barrier to moisture, air, odors, light, and microorganisms Good flexibility Surface resilience Excellent malleability and formability Recyclable Resistant to heat process It is often used to metallize other films because this treatment helps to improve barrier properties to moisture, oils, air, and odors Good heat sealability Excellent gas, odor, and water barrier properties Good resistance to oil and organic solvents Excellent oil and grease resistance Low softening temperature Good processing properties Flexible Strong Easy to seal Resistant to moisture Relatively transparent Good resistance to chemicals and water vapor Stiff Strong Tough Resistant to chemicals and moisture Easy to process Easy to form Good barrier properties to water vapor and oxygen It could be copolymerized with ethylene to produce EVOH with improved water vapor properties Good barrier to gases (oxygen and carbon dioxide) and moisture Good resistance to heat, mineral oils, solvents, and acids, but not to bases Glasslike transparency Shatter resistance Good resistance to chemicals and water vapor High melting point (160  C) When used in combination with an oxygen barrier such as ethylene vinyl alcohol or polypropylene provides strength and moisture barrier

l

Breakable Poor portability

Useful for heat sterilization of both low-acid and high-acid foods l Light-sensitive foods

l

High cost Inability to be welded, which renders it useful only for making seamless containers l Limited structural strength

l

l

l

l

Its high barrier properties make it not suitable for applications to respiring products

l

l

Moderate gas and water barrier properties

l

l l

Poor gas barrier properties Translucency

l

Permeable to gas

Soft drink Cans l Seafood l Pretreated closures

l

Bottles for mineral water, fruit squash, cooking oils l Meat wrap l Bread and frozen food bags l Flexible lids – squeezable food bottles

l l

l

Barrier properties are moisture dependent

l

Very susceptible to heat degradation No biodegradability

l

High thermal expansion coefficient which limits its high temperature applications Susceptible to UV degradation Poor resistance to chlorinated solvents and aromatics High flammability Susceptible to oxidation

l

l

l

l l l l

Chilled or sterilized meat, cheese Poultry products

l

Bottles for milk, juice, and water Cereal box liners, margarine tubs, and grocery

Beverages and mineral waters Plastic bottles for carbonated drinks

Hot-filled and microwavable packaging l Yogurt containers and margarine tubs l Ketchup and salad dressing bottles

(Continued)

Packaging and Shelf Life of Produce

Table 1

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Properties of food packaging materialsdcont'd

Material

Advantages

Disadvantages

Food application

Polyethylene naphthalate (PEN)

l

l

l

Bottles for beverages such as beer

l

l l

Ethylene vinyl alcohol (EVOH)

l l

Barrier properties for carbon dioxide, oxygen, and water vapor superior to those of polyethylene terephthalate (PETE) Protection against transfer of flavors and odors High glass transition temperature Excellent barrier to oil, fat, and oxygen Good processing properties

High costs

l

Moisture sensitive, thus it is used in multilayered coextruded films in situation where it is not in direct contact with liquids l Not suitable for high-respiring products

l

Poor barrier properties

l

It is used as a barrier layer in combination with other polymers and in this case it is used for: ketchup juices baby foods ultrahigh-temperature processing milk coffee dry snacks beer No food applications

l

Tends to absorb moisture from environment Higher cost among plastics High costs Poor barrier properties Non-heat sealable Moisture sensitive

l

Boil-in bag packaging

l l l l l l l

Polystyrene (PS)

l l l

Polyamides

l l

Available in rigid and foam form Inexpensive Recyclable Good barrier properties High resistance to stress cracking

l

Polylactic acid (PLA) l Paper and paperboard

l

Biodegradable l Good strength-to-weight characteristics l Recyclable l Low cost

l l l l

Kraft paper for: flour, sugar l dried fruits l vegetables Sulfite paper for: l biscuits and confectionary Greaseproof paper for: l snack foods, cookies l oily foods l

properties, vary with the intrinsic characteristics of the polymeric material such as degree of crystallinity, polymer nature, thermal and mechanical treatments before and after food contact, chemical groups present in the polymer, degree of cross-linking, and glass transmission temperature (Mrkic et al., 2006). In order to achieve a good barrier in laminates, it is possible to work on the material surface properties as the orientation of macromolecular chains may reduce gas diffusivity (Lazic et al., 2010) or to combine different layers and various types of resins increasing the barrier properties of the final package. Other factors can also influence the barrier properties of a specific polymer, for example, food contact, environmental conditions (temperature and humidity), film structure, film permeability, thickness area, and difference in pressure or concentration gradient through the film. The diffusion rate depends on the size, shape, and polarity of the penetrating molecule and on the crystallinity, degree of cross-linking, and polymer chain segmental motion of the polymer matrix. Gas substances are unable to permeate through the polymer crystallites because they are insoluble in the material. Thus, the gas permeation into semicrystalline polymers is then confined into the amorphous regions. The reduction in permeability value is proportional to the volume fraction of the crystalline phase. In relation to these aspects, generally plastics are relatively permeable to small molecules such as gases, water vapor, organic vapors, and liquids providing a broad range of mass transfer characteristics. The most important barrier properties of polymer films used in food packaging application refer to oxygen, water vapor, and carbon dioxide transmission rate (Siracusa et al., 2008). When a polymer film packaging has low oxygen permeability coefficient, the oxygen pressure inside the container drops to the point where the oxidation is delayed, extending the shelf life of the product. This value is important especially in produce. The water vapor barrier properties of a packaged food product whose physical and chemical deteriorations are related to its moisture content are of great importance, in maintaining or extending its shelf life. For example, in fresh food it is important to avoid dehydration while for bakery or delicatessen it is necessary to avoid water permeation. As for oxygen and water vapor, also carbon dioxide barrier properties are of particular importance in food packaging applications.

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For polymers, transmission rates are inversely proportional to the layer thickness. For multilayers, the total transmission rate can be calculated in good approximation by reciprocal addition of the transmission rates of individual layers. The degree of polymer crystallinity may influence the permeability of oxygen; in fact, it has been demonstrated that the oxygen permeability decreases from 38% to 19% as the crystallinity increases from 60% to 69% (Lee et al., 2008). Mrkic et al. (2007) studied the influence of temperature and mechanical stress on gas barrier properties of commercial polymers based on PE (polyethylene), biaxially oriented polypropylene (BOPP), and PA (polyamide). They found that increasing the mechanical stress caused changes on barrier properties, but it did not change the thermal behavior of the polymer matrix.

Active Packaging Active packaging has been designed as a system in which the product, the package, and the environment interact in a positive way in order to extend the shelf life or to achieve some characteristics that cannot be obtained otherwise. It has been defined as a packaging system that actively changes the condition of the package to improve food safety or sensory properties, without altering the quality of food (Robertson, 2006). All active technologies involve some physical, chemical, or biological action in order to modify the interactions between the package, the product, and the package headspace to achieve certain desired outcomes (Brody et al., 2001). Gas absorbing/emitting packaging is a group of technologies that uses packaging films or sachets to absorb or to emit gases from/to the package headspace maintaining a favorable internal package environment and extending product shelf life. Oxygen scavengers are easily oxidizable substances included into the packaging system that remove oxygen through chemical reactions. The reactive substance is usually contained in sachets made of a material highly permeable to air, but it can also be included in bottle closures or in plastic film matrixes. The most common oxygen scavengers are those based on ferrous iron; these types of scavengers were commercially developed by Japan’s Mitsubishi Gas Chemical Company under the name ‘Ageless’ (http://www.mgc.co.jp/ eng/products/abc/ageless/eye.html). The reactive substance is ferrous iron oxide that oxidizes to the ferric state in presence of enough water. Instead of sachets, iron might be spread over the entire surface area of the film, as realized by Multisorb Technologies in its ‘Fresh Max’ (http://www.multisorb.com/news-and-events/news/multisorbs-freshmax-self-adhesive-oxygen-absorber-wins-polagrafoods-gold-medal-competition-in-poland/) and by Grace company in its ‘Darex’ (https://grace.com/packaging/en-us/ oxygen-scavenging-technology), that are oxygen scavengers incorporated into crowns, cans, and other metal and plastic closures. In particular, Darex is used for shelf life extension of different products such as beer, wine, tomato-based products, fruit, and drinks. Oxygen scavengers in sachet form have shown to extend bread’s and pizza’s shelf life up to 45 days, retarding mold growth (Brody et al., 2002). These active systems can be projected using also other substances different from iron such as immobilized enzymes, sulfites, ascorbic acid, and glucose oxidase. Ascorbic scavengers can be oxidized to dehydroascorbic acid which is less harmful with respect to iron compounds and acts also in presence of carbon dioxide. Oxygen absorbers or scavengers are commonly found in meat, poultry, coffee, and baked and dry foods. Although sachets work well in many applications, they are not appropriate for every situation such as in the case of liquid foods (Yam et al., 2005). Another system often used in food sector is the ethylene scavenger. Ethylene is considered as a problem in postharvest handling of horticultural products, being responsible for undesirable effects on fruits and vegetables: softening, ripening, specific postharvest disorders, and acceleration of their respiration rates. When ethylene is removed from the fresh fruit and vegetable environment, the ripening and deterioration processes of plant products are slowed and as consequence, shelf life extended. Ethylene scavengers based on potassium permanganate are only available in sachets because of their toxicity when in contact with foods (Brody et al., 2001). These scavengers generally consist in alumina pellets impregnated with potassium permanganate; the function of alumina is the entrapment of gas acting as a carrier of permanganate. One commercial example is ‘Air Repair’ from DeltaTrak (http://www.deltatrak.com/products/ethylene-absorbers) in which potassium permanganate is contained in alumina beads. Another system to remove ethylene, much more popular in Japan, consists in a metal catalyst on an activated carbon support. Carbon dioxide absorbers might be useful to remove the produced gas from the package, avoiding food deterioration and/or package destruction. The gas scavenger sachets ‘FreshLock’ or ‘Ageless’ are used in coffee to delay oxidative flavor changes and to absorb the occluded CO2 that, if not removed, would cause the package to burst. Another important feature in food preservation is the water control. Depending on the food product in question, it might be required to keep the moisture out of the package or in the package. In most cases as stated before, the packaging material itself is responsible for the control of moisture transfer between the internal and external environment, providing an adequate barrier. In other circumstances a greater control is needed to avoid the buildup of liquid water inside the package, such as transpiration in fresh products, melting of ice during fish transportation, temperature fluctuation in high-water-activity food packages, and drip of tissue fluid from cut meats. Removal of liquid water is usually realized by using absorbent pads or sheets. In these systems, a superabsorbent polymer is placed between two layers of a microporous or nonwoven polymer, such as polyethylene or polypropylene. These polymer ‘sandwich’ absorbents are used, for example, under meat pieces in order to absorb drip. The reduction of the in-pack relative humidity, in order to control the excess of moisture, has been made by means of different approaches, as for example, placing humectants between two layers of a highly water vapor permeable plastic film or using sachets of inorganic desiccant salts, such as sodium chloride. Well-known moisture absorbers are silica gels, often applied when it is needed to maintain dry conditions as in dry foods.

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Another category of active packaging very useful for produce shelf life prolongation is represented by solutions containing antimicrobial/antioxidant compounds. Generally speaking, packaging systems with active compounds can take several forms including: sachets, filters, or pads containing volatile agents into packages; volatile and nonvolatile antimicrobial agent’s incorporation directly into polymers; l absorbers or coatings onto polymer surfaces; l active agents immobilized on polymer surface; and l inherently antimicrobial polymers. l l

One of the most popular active systems consists in the ethanol emitters. Ethanol is considered an antimicrobial agent and creates an antimold atmosphere, particularly effective in extending the shelf life of high water active baked foods. Commonly, ethanol is encapsulated in a carrier material enclosed in sachets with selective permeability to ethanol. This system allows the release of ethanol vapor into the packaging headspace. The most commercially used system is the ‘Eticarp’ developed by Freud industrial. This system consists of a silicon dioxide powder containing alcohol and water. The sachet is made of laminate paper/ethyl vinyl acetate, which is a low barrier to ethanol vapor. Ethanol emitters are used extensively in Japan to extend the shelf life of high-ratio cakes and other high-moisture bakery products (Day, 2003). Research has also shown that such bakery products packed with ethanol-emitting sachets did not get as hard as the controls, and results were better than those using an oxygen scavenger alone to inhibit mold growth. Ethanol-emitting sachets are also widely used in Japan for extending shelf life of semimoist and dry fish products (Day, 2003). An alternative to the incorporation of antimicrobial compounds during extrusion is to apply the antimicrobial additives as a coating. This has the advantage of placing the specific antimicrobial additive in a controlled manner without subjecting it to high temperature or shearing forces. In addition, the coating can be applied at a later step, minimizing the exposure of the product to contamination. Raybaudi-Massilia et al. (2008) studied a coating-release system to verify the combined effects of malic acid and essential oils of cinnamon, palmarosa, and lemongrass (0.3% and 0.7%) and their main active compounds (eugenol, geraniol, and citral, 0.5%) on microbiological and physicochemical shelf life of fresh-cut ‘Piel de Sapo’ melon (Cucumis melo L.). The active compounds were incorporated into an alginate-based edible coating. Melon pieces were inoculated with Salmonella Enteritidis (108 CFU ml 1) culture before applying the coating. The incorporation of essential oils or their active compounds into the edible coating prolonged the microbiological shelf life by more than 21 days. Rojas-Graü et al. (2007) investigated the effect of lemongrass, oregano oil, and vanillin incorporated in apple puree-alginate edible coating on the shelf life of fresh-cut ‘Fuji’ apples. During 21 days of storage at 4  C, the coating with vanillin (0.3% w/w) was the most effective in terms of sensory quality. All the other studied antimicrobial coatings significantly inhibited growth of psychrophilic aerobes, yeasts, and molds. As reported by Krasaekoopt and Mabumrung (2008), the effectiveness of chitosan incorporated in the edible methyl-cellulose coating on the microbiological quality of fresh-cut cantaloupe was evaluated. During storage at 10  C for 15 days, applications of 1.5% and 2% chitosan in the coating reduced growth of some pathogens. As regards the incorporation of antimicrobial substances into the packaging material during extrusion, natural antimicrobials have been incorporated into paper, thermoplastics, and thermosets and tested against Listeria monocytogenes, Escherichia coli, and molds. In Japan, silver-substituted zeolites represent the most common antimicrobial substances added to polyethylene, polypropylene, and nylon (Brody et al., 2001). In addition to silver zeolites, propionic, benzoic, sorbic, and lactic acids have been added to ethylene vinyl alcohol or linear low-density polyethylene (LLDPE) to contrast mold’s growth. LLDPE with 0.05% of methyl chavicol proved to be effective against E. coli (Suppakul et al., 2003) while the same polymer with ascorbic acid and carvacrol showed a better action against E. coli in ground beef. The disadvantage of producing films containing active agents is poor cost-effectiveness since antimicrobial material not exposed to the surface of the film is generally not totally available to the antimicrobial activity. An alternative is to apply the antimicrobial additive in a controlled matter; for example, it can be incorporated into the food-contact layer of a multilayer packaging system (Suppakul et al., 2003). The release packaging can overcome the limitations of direct addition of active agents in food by continuously replenishing the compounds to the food surface and maintaining in the food the concentration to achieve a desired shelf life (Mastromatteo et al., 2010). Controlled release packaging is also known as time-release or slow-release packaging of active substances, drugs such as antibiotics and antimicrobials for various food packaging applications (Buonocore, 2003b). Potassium sorbate exerted antibacterial and antimycotic effect when added to high-density polyethylene (HDPE) and Low-density polyethylene (LDPE) films and slowly released on American cheeses. Released sorbate from HDPE films was found to be effective in enhancing cheese storage for 5 months at room temperature (Szente and Szejtli, 2004). The migration of a substance may be achieved by direct contact between food and packaging material or through gas phase diffusion from packaging layer to food surface (Coma, 2008). The theoretical advantage of volatile antimicrobials is that they can penetrate the bulk matrix of the food and that the polymer need not necessarily directly contact the packaged food. Nadarajah et al. (2005) tested the antimicrobial activity of allyl-isothiocyanate, a volatile and aliphatic sulfur-containing compound, potentially found in black and brown mustard associated with a filter paper disk which was packaged with a ground beef patty. The patty and the filter paper were placed together in a bag made of a multilayer system. Due to the release of the compound into the headspace, E. coli 0157:H7 in fresh ground beef during refrigerated or frozen storage was reduced. Among the release device categories, a further division would be made between controlled and uncontrolled release systems. Even though uncontrolled delivery packages intended for food applications are the most abundant, controlled release systems are of industrial relevance, due to their aptitude to prevent sensorial or toxicological problems or inefficiency of the system, caused by a too high or a too low concentration of delivered substance. Although data about numerical methods to describe controlled release mechanisms exist, most of these studies

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have been carried out using food simulating systems, without taking into account the potential effects of such a type of release system on real food cases (Mastromatteo et al., 2010). The release rate of an active compound from the packaging to the food can be realized by means of two mechanisms: reservoir and swelling system. The former consists of an active agent contained within a rate-controlling microporous, macroporous, or nonporous barrier. The release rate from a reservoir system depends on the thickness, the area, and the permeability of the barrier. In a reservoir containing an excess of active agent, the constant release rate follows a zero-order kinetic. On the other hand, in a swelling-controlled system, the active agent, dissolved or dispersed in a polymeric matrix, is unable to diffuse to any significant extent within the matrix because of its low diffusion coefficient. When the polymer matrix is placed in a thermodynamically compatible medium, the polymer swells owing to absorption of fluid (penetrant) from the medium, and the active agent diffusion coefficient in the swollen part of the matrix increases and then it diffuses out (Buonocore et al., 2003a,b; Flores et al., 2007). The immobilization of an antimicrobial substance to the packaging polymer requires the presence of functional groups on both the antimicrobial substance and the polymer (Conte et al., 2006). Since peptides can be covalently immobilized through amino and carboxylic groups, they may be suitable for attachment to functionalized polymer surfaces. A 14-amino-acid residue peptide was immobilized on polystyrene by solid phase peptide synthesis and tested against several food-borne microorganisms (Appendini and Hotchkiss, 2001). However, the low availability of antimicrobial substances and the limited choice of polymers with adequate properties limit the development of these kinds of active packaging. It is therefore essential to search for new materials and new strategies to combine them with antimicrobial substances. Several types of active compounds have been used in active packaging, organic acids, enzymes, species, essential oils, bacteriocins, antioxidant phenols, antibiotics, and metals (Conte et al., 2007; Incoronato et al., 2011; Mastromatteo et al., 2009; Bodaghi et al., 2013; Sanches-Silva et a., 2014). The use of nanoparticles as carriers to protect and control the release of active compounds represents the most valuable and successful tool to develop an effective active packaging system. Various approaches have been studied, among which Laser Ablation Synthesis (LASis) and chemical modification of inorganic particles are the most promising. LASis consists in ablating a metal target in a liquid environment by pulsed laser irradiation, resulting in the formation of a nanoparticles colloidal suspension (Ancona et al., 2014; Conte et al., 2013; Longano et al., 2012). Chemical modification of inorganic particles is an innovative and successful approach for the protection and intercalation of active compounds in between the pore/clay galleries. Interestingly, inorganic nanocarrier can be mesoporous silica such as Santa Barbara Amorphous 15 as well as layered double hydroxide which constitute a very attractive class of hosts capable of producing inorganic–organic intercalation compounds because of their anion-exchange properties (Siefker et al., 2014). In recent years halloysite nanotubes, which are naturally occurring members of the kaolin family of aluminosilicate clay and characterized by a hollow tubular structure, emerge as promising nanoscale containers, being not hazardous for the environment, and available inexpensively from natural deposits (Lavorgna et al., 2013, 2014).

Intelligent Packaging Intelligent packaging is a system capable of carrying out intelligent functions (such as detecting, sensing, recording, tracing, communicating, and applying scientific logic), enhancing in this way the safety and improving consumer’s awareness about the product’s quality. The main function of intelligent packaging is communication, while active packaging is strongly related to food protection. Thus, in the total packaging system, intelligent packaging is the component responsible for sensing the environment and processing information, while active packaging is the component responsible for taking some actions (for example, release of an antimicrobial substance) to protect the food product. A package can be designed as ‘intelligent’ if it has the characteristic to track the product, sense the environment inside or outside the package, and communicate with humans. For example, an intelligent package can monitor the quality/safety condition of a food product and provide early warning to the consumer or food manufacturer. There are two basic types of intelligent packaging: data carriers (barcode labels and radiofrequency identificators – RFID), used to store and transmit data, and package indicators (such as time–temperature, gas indicators, freshness and pathogen indicators). Barcodes consist of a pattern of bars and spaces that identify a specific food product in a store and enable to trace its evolution in the grocery industry. The RFID tag is an advanced form of data carrier for automatic product identification and traceability. Although RFID has been available for many years for tracking expensive items and livestock (Anonymous, 2003), its broad application in packaging has begun only at the beginning of the 21st century. In a typical RFID system a reader emits radio waves to capture data from RFID tag and the data are then passed onto a host computer (which may be connected to a local network or to the Internet) for analysis and decision making (Want, 2004). ThermAssureRF is a new RFID-based system that combines tracking and temperature measurement to ensure foods such as meat, fruit, and dairy products remain at a safe temperature during transportation and storage. It is currently being used by companies that ship wine, produce, seafood, meat, and poultry. There is no shortage of published examples of RFID applications in the food industries. Unilever tracks ice-cream temperatures from manufacture to retail display cabinets in order to ensure quality assurance throughout the cold chain. Manor monitors supermarket freezers and refrigerators. In these cases the aim of RFID tracking is to decrease shrinkage due to food spoilage and to have a faster response to equipment failures. Wal-Mart stores and more recently Carrefour and Metro have adopted (and asked suppliers to adopt) digital-tagging technologies, including RFID.

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Temperature is usually the most important environmental factor influencing the kinetics of physical and chemical deteriorations, as well as microbial growth in produce. This parameter is measured through time–temperature indicators (TTIs) that are typically small self-adhesive labels attached onto shipping containers or individual consumer packages. These labels provide visual indications of temperature history during distribution and storage, which is particularly useful for chilled or frozen food products. They are also used as ‘freshness indicators’ in order to determine the remaining shelf life of produce. The TTIs present on the market have working mechanisms based on different biological, chemical, and physical principles. For the first type, the change in biological activity of microorganisms, spores, or enzymes is the basic working principle. Others are based on a purely chemical or physical response toward time and temperature, such as an acid–base reaction, melting, or polymerization. A commercial example of TTIs is ‘Fresh-Check’ by LifeLine (http://www.fresh-check.com/), which is a full history indicator whose working mechanism is based on the color change of a polymer formulated from diacetylene monomers. It consists of a small circle of polymer surrounded by a printed ring for color reference. The polymer, which starts lightly colored, gradually deepens in color to reflect the cumulative exposure to temperature. The changes in polymer color rate are proportional to the rate of food quality loss: higher is the temperature, more rapidly the polymer changes its color. Another example is the Vitsab indicator (http://vitsab.com/), which is a full history indicator based on an enzymatic reaction. The device consists of a bubble-like dot containing two compartments: one for the lipase enzyme solution plus a pH-indicating dye compound and the other for the substrate, consisting primarily of triglycerides. The dot is activated at the beginning of the monitoring period pressing on the plastic bubble that breaks the seal between compartments. The ingredients are mixed, and as the reaction proceeds a pH change is observed that results in a color change. The dot, initially green in color, becomes progressively yellow during the product storage. Over the years, Vitsab has supplied the fish producers with indicators for temperature control during transport from the producer to the customer, anywhere in the world. More than one billion portions of fish have been checked. Vitsab TTI label could monitor time/ temperature conditions for toxin from Clostridium botulinum. Gas indicators are another intelligent system, developed in the form of label or printed directly on packaging films to detect changes in the gas composition, monitoring in this way the quality and safety of food products. Oxygen indicators are the most common gas indicators for food packaging applications, because oxygen can cause oxidative rancidity, color change, and microbial spoilage. A typical oxygen indicator is composed by a redox dye (such as methylene blue), an alkaline compound (such as sodium hydroxide), and a reducing compound (such as reducing sugars). Smiddy et al. (2002) used oxygen indicators to detect improper sealing and quality deterioration of modified atmosphere packages containing pizza or cooked beef. Many visual oxygen indicators for food applications, consisting mainly of redox dyes, have been patented (Davies and Gardner, 1996; Krumar and Karel, 1992; Mattila-Sandholm et al., 1995). Such devices have been tested as leak indicators in modified-atmosphere-packaged minced steaks and minced-meat pizza. Another example of oxygen indicator is the UPM Shelf Life Guard developed by UPM, Helsinki, Finland, which is an indicator that monitors the presence of oxygen in modified-atmosphere-packaged meat, sausage, poultry, and fish products. The label contains a redox dye, held between laminated layers, which reacts with oxygen changing its color. Indicators for water vapor, carbon dioxide, ethanol, and hydrogen sulfide are other examples of gas indicator systems. For example, Hong and Park (2000) used a carbon dioxide indicator consisting of a carbon dioxide absorbent and a chemical dye in a polymeric film to measure the degree of fermentation in kimchi products during storage and distribution. To monitor the microbiological quality of a food product, freshness indicators have been also developed. Their function is based on a reaction between the indicator and the metabolites produced by the microorganisms during their growth. A specific indicator material has been developed for the detection of E. coli O157 enterotoxin, based on color change of a chromogenic substrate, determined by an enzymatic reaction. A myoglobin-based indicator for modified-atmosphere-packed poultry meat helps to indicate spoilage by detecting presence of hydrogen sulfide (H2S) formed upon spoilage (Smolander et al., 2002). Pacquit et al. (2006) developed a colorimetric dye-based sensor that detects the presence of total volatile basic nitrogen (TVB-N), which is a result of fish spoilage. Practically, these systems could be prepared by entrapping within a polymer matrix a pH-sensitive dye (e.g., bromocresol green) that responds, through visible color changes, to the spoilage volatile compounds produced during fish deterioration. The use of a colorimetric mixed-dye-based food spoilage indicator to other food products (such as easily prepared foods, fresh and processed meat, poultry, bakery, desserts, fresh-cut fruits, and vegetables) could be a possible future area of research. A pH indicator, a fast and simple visual response allowing for the determination of fish freshness by a color change, has been described in many previous studies (Pacquit et al., 2007; Byrne et al., 2002). When a fish product spoils, a pH increase caused by production of TVB-N is reflected in a pH-sensitive indicator that detects the chemical composition in the packaging headspace. The main principle of action of this freshness indicator is a pH-sensitive dye that changes color when placed in an acidic or basic environment. The freshness indicator’s response can be monitored at regular intervals using a color difference meter to represent fish freshness. Another important information that a consumer need to know is fruit ripeness. Ripeness biosensors have been worked out to know when fruits reach their optimal state of ripeness. These biosensors are in form of labels and react with fruit aromas released during ripening. Consumers are able to choose fruits with their preferred ripeness viewing the sensor change in color, from red (unripe) to yellow (ripe). These sensors have been applied to pears and could also be applied as ripeness indicator for kiwifruit, melon, mango, avocado, and other stone fruit. Considering the importance of intelligent packaging allowing consumer’s awareness about the security and food freshness by means of a nondestructive method, a multidisciplinary approach is needed to develop smaller, more powerful, and less expensive smart package devices for intelligent packaging applications.

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Future Trends Active and intelligent packaging are emerging as new branches of packaging science that offer exciting opportunities for enhancing food safety, quality, and convenience. The advancement in this technology will require researchers to continue to use nontraditional packaging approaches to meet new challenges. Even though much progress has been made, further research still needs to be conducted on how these solutions may affect product characteristics. Active packaging is used largely in Japan, but also its use is beginning to increase in Europe. The issues of acceptance by industries as well as the more conservative behavior of European consumers regarding food innovations are key points that still need to be addressed. Low diffusion of active and intelligent packaging in the European Union countries has been related to two main reasons: the first is connected to costs and the second refers to safety concern. Advanced smart-package devices such as biosensors are still at an early development stage, whereas most of the prototypes are limited by slow response time or short shelf life. Yet possibilities also exist in combining biotechnology and nanotechnology to develop biosensors to overcome these and other limitations. Other future research opportunities may be directed toward the integration of data carriers (such as barcode and RFID) and package indicators (such as TTI and gas indicator) with active packaging solutions into small hybrid devices. Active and intelligent packaging systems are an emerging and exciting field of food technology which can confer many preservation benefits on a wide range of products. As more companies become aware of the economic advantages of using these packaging technology and consumers accept this approach, this technology will likely emerge. Manufactures seek out more cost-effective solutions without compromising shelf life performance while consumers are demanding for more natural, disposable, potentially biodegradable, and recyclable packaging. During the early twentieth century, substantial developments were made on both rigid and flexible packaging materials, thereby increasing the options available for product quality and shelf life improvement. To meet industries’ growing demand for recyclable or natural packaging materials and consumer request for safer and better quality foods, new and novel food-grade packaging materials or technologies have been and still need to be developed. Examples of these packaging materials include bio-based polymers, or packaging made from agricultural or marine sources and edible polymers as carriers of antimicrobial substances, flavors, antioxidants, and nutraceutical. Therefore the development of new technologies to improve the performance of bio-based polymers is one of the major issues for future research. Currently many studies are done on laboratory scale, but further research should be focused on commercial scale in order to provide more accurate information.

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