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The benefits of processing and packaging
Trends in Food Science & Technology 22 (2011) 127e137
Review
The benefits of processing and packaging *, Mario Scetar and Kata Galic Mia Kurek University of Zagreb, Faculty of Food Technology and Biotechnology, Pierottijeva 6, 10000 Zagreb, Croatia (e-mail: [email protected]) Food processing and preservation are generic terms that cover all aspects of extending the shelf life of foods. A number of novel thermal and non-thermal processing methods are actively undergoing research and development. A key step that needs addressing is finding the best packaging materials for commodities which preserve the benefits of improved product quality imparted by preservation technologies.
Introduction Food is packaged for storage, preservation, and protection traditionally for a long time. These three are the basic functions of food packaging that are still required today for better maintenance of quality and handling of foods. However, following the evolution of modern society and lifestyle, the significance of several functions of packaging is also shifting from one aspect to another (Brody, Bugusu, Han, Sand, & McHugh, 2008). There is a trend of changes in the priority of these functions with time and social circumstances. The distribution of priority of each packaging function is highly dependent on the commodities and, therefore, the properties of packaged foods. The commercialization of a newly developed non-thermal processing system essentially requires deep research on the packaging material properties and the interactions between the packaging materials and non-thermally processed foods. The packaging for non-thermally processed foods may necessitate extra functions of packaging for successful commercialization. Packaging materials should have strong physical and mechanical resistance to the non-thermal * Corresponding author. 0924-2244/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2010.04.001
process mechanisms. Non-thermal processes do not utilize increased temperature to inactivate decomposing microorganisms and enzymes. This is the biggest advantage of non-thermal processes because this low-temperature pasteurization does not overcook food and/or degrade foods thermally (Min & Zhang, 2005). Furthermore, hurdle technology is the term often applied when foods are preserved by a combination of processes. In general, hurdle technology is now widely used for food design in making new products according to the needs of processors and con´ lvarez, 2007; Siripatrawan & Jantawat, 2008). sumers (A This low-temperature treatment widens the selection of packaging materials and system does not require high melting temperature for heat seal. These methods produce far less volatile odour of plastics, additives, and printing solvent. This is very beneficial to high-fat foods and frozen/refrigerated foods. Since some of these techniques might require the processing of foods inside their package, it is important to understand the interaction between the package and the process itself (Clough, 2001; Devlieghere, Vermeiren, & Debevere, 2004; Ozen & Floros, 2001). Proper selection and optimizing of packaging are of major importance to food manufacturers due to aspects such as economy, marketing, logistics, distribution (Lelieveld, 2007; Min & Zhang, 2005; Trienekens, Hagen, Beulensc, & Omta, 2003), environmental impact of the packaging as well as the consumer demands (Ba´na´ti, 2005). Food-package interaction The quality of the packaged food is directly related to the food and packaging material attributes (Cooksey, 2007; Lee, Yam, & Piergiovanni, 2008). Most food products deteriorate in quality due to mass transfer phenomena, such as moisture absorption, oxygen invasion, flavour loss, undesirable odour absorption, and the migration of packaging components into the food (Kester & Fennema, 1986; Sajilata, Savitha, Singhal, & Kanetkar, 2007). The phenomena can occur between the food product and the atmospheric environment, between the food and the packaging materials, or among the heterogeneous ingredients in the food product itself. Thus, the rate of transport of such reactants across the partial barrier of the package wall can become the limiting factor in shelf life (Giacin, 1995; Hotckiss, 1995). Non-thermal processing in sequence with packaging requires transfer of the food into the package by aseptic or
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other means under reduced or elevated oxygen. After packaging, non-thermal processing generally requires hermetic closure before processing and maintenance of hermetic closure throughout the process and distribution. Non-thermal process also may be conducted while in package prior to hermetic closure. Critical protective barrier properties of packaging materials must be preserved to prevent chemical, physical, or microbial degradation of contents after nonthermal processing. Therefore, it is necessary to understand the process parameters and mechanisms/kinetics of the non-thermal process and their effects on packaging material properties. Some examples will be given to illustrate the possible issues arising from novel trends in food processing and packaging. High-pressure technology involves different packaging considerations, based on whether a product is processed in-container or packaged after processing. The packaging material must be able to withstand the operating pressures, have good sealing properties, and the ability to prevent quality deterioration during the application of pressure. At least one interface of the package should be flexible enough to transmit the pressure. Thus, rigid metal, glass, or plastic containers cannot be used. Due to the fact that air or gases are very compressible under high pressure, the more the headspace, the bigger the deformation strains on the packaging materials. The presence of headspace must be kept as small as possible (Rastogi, Raghavarao, Balasubramaniam, Niranjan, & Knorr, 2007). To increase the shelf life of processed foods, the package must be designed with an adequate water vapour (WV) and/ or gases (O2, CO2, etc.) permeabilities. According to literature data laminates, such as, PP/EVAL/PP; PP-O/PVAL/ PE; PA/PE; PET/PVDC/PE; PA/PP/PE etc., (Table 1) show no significant changes in gas barrier properties (Lambert et al., 2000; Masuda, Saito, Iwanami, & Hirai, 1992). The effect of high-pressure processing (HPP) treatment on functional properties of packages showed, in some cases, significant loss of heat sealability (PA/PE; PE/PA/EVAL/PE; PET/PE/EVAL/PE) or increase of migration levels (PE-LD/EVAC/VDC), (Dobias, Voldrich, Marek, & Chuda´ckova´, 2004; Rivas-Ca nedo, Ferna´ndezGarcı´a, & Nu nez, 2009). Furthermore, delamination between PP and Al, in PE/PA/Al/PP laminate, was observed in meal-ready-to-eat pouches treated at 200 MPa and 90 C for 10 min (Schauwecker, Balasubramaniam, Sadler, Pascall, & Adhikari, 2002). The packaging materials for irradiation (Table 1) should be chemically stable under the radiation dose to prevent polymer degradation and low molecular weight hydrocarbons and halogenated polymers formation which can migrate into foods (Clough, 2001; Haji-Saeid, Sampa, & Chmielewski, 2007; Oral, Rowell, & Muratoglu, 2006; Pentimalli et al., 2000; Rojas De Gante & Pascat, 1990). Radiolysis products (RPs) formed upon irradiation of a polymer or adjuvant could migrate into food and affect odour, taste, and safety of the irradiated food. Radiation
does not generally affect all properties of a polymer to the same degree. Barrier properties (Table 1) of some monofilms (PE-HD, PE-LD, PS, BOPP) where not significantly changed by irradiation (Rojas De Gante & Pascat, 1990). As for the laminates, barrier properties either decrease, as in the case of BOPP/CPP and PET/PVDC/PE (Kim-Kang & Gilbert, 1991; Mizani, Sheikh, Ebrahimi, Gerami, & Tavakoli, 2009), or are not significantly affected, ex. PA/PVDC/EVAC, PET/PE/EVAL/PE and PET/ PET/PE-LLD (Descheˆnes et al., 1995; Mizani et al., 2009; Riganakos, Koller, Ehlermann, Bauer, & Kontominas, 1999), with applied radiation doses. Modified atmosphere packaging (MAP) has been intensively investigated to minimize quality changes of irradiated foods during storage. However, an attention needs to be drawn in applying MAP for the packaging of non-thermally processed foods since MAP can selectively change the microbiology of foods. The suppression of aerobic spoilage microorganisms will decrease competition for growth and provide sufficient time for the growth of pathogenic microorganisms, especially if the MAP foods received a nonsterilizing treatment (Hotchkiss & Banco, 1992). Aseptic packaging is considered the most appropriate way of packaging for pulsed electric fields (PEF) processed foods. Traditional methods for juice packaging aim to reduce the exposure of the juice to oxygen through the use of high barrier materials such as glass or foil laminates in brick packs, with or without nitrogen flushing or improving gas barrier of PET by blending with aromatic polyamides (Hu et al., 2005). The use of oxygen scavengers with an appropriate packaging material can further reduce the presence of dissolved oxygen in the juice or present initially in the headspace (Ros-Chumillas, Belissario, Iguaz, & Lo´pez, 2007; Zerdin, Rooney, & Vermue¨, 2003). Unlike glass and PET, PE-HD and PE-LD bottles were not effective at retarding degradations of flavour compounds and vitamin C of PEF-treated orange juice during storage at 4 C for 112 days, which might be due to their relatively low barrier property of polyethylene to oxygen (Ayhan, Yeom, Zhang, & Min, 2001). The degradation of lycopene of PEF-processed tomato juice in a PP tube was found most significant during the first seven days of the storage at 4 C (Min, Jin, & Zhang, 2003). The main cause of carotenoid degradation in foods is oxidation (Thakur, Singh, & Nelson, 1996), and thus the significant reduction was considered due to oxygen availability in the headspace of the PP tubes (Min et al., 2003). The MAP, which limits oxygen in the headspace, may be applied as a complement to PEF to reduce oxidation of PEF-processed food products. For pulsed UV/white-light emission process, the packaging material must be transparent during pulsed light emission. Due to poor penetrative properties, UV light is more or less limited to surface applications, but it shows promise as a post-packaging treatment. For example UV irradiated beef steak, packaged in PE pouches with modified
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Table 1. Effects of new processing techniques on the packaging material properties Packaging material
Effect of processes
Reference
Barrier properties and structural characteristics of material were not affected (400 MPa, for 30 min at 25 C)
Nachamansion, 1995
PE/PA/EVAL/PE; PET/PE/EVAL/PE; PE-LD/PA/PE-LD; PE-LD/PE-LLD; PPantifog; BOPP; PA/PE; PE-LD/EVAL/PE-LD/PETA/expPET/PET-A;
Loss of heat sealability, increased migration levels (600 MPa for 60 min, at room temperature). Further confirmation needed
Dobias et al., 2004
PET/PA/Al/PP PA/EVAL/PE
No detectable PG migration PG migration was similar at 30, 50, and 75 C after 10 min. under atmospheric pressure. PG migration into the PA/EVAL/PE significantly decreased when treated with high pressure (200, 400, 690 and 827 MPa) at 30, 50, and 75 C At 75, and 50 C, the PG migration was significantly higher than the amounts detected at 30 C. Visible signs of delamination between the PP and Al layers (at200 MPa and 90 C for 10 min)
Schauwecker et al., 2002
The increase in permeance was less than 11%. No significant changes in tensile strength, elongation and modulus of elasticity (600e800 MPa for 5,10 and 20 min at 45 C). Prolonged exposure had a greater effect on the permeance of inorganic layers in some films, than lower pressure/time combinations. Mechanical analysis is not a good analytical approach to determine the suitability of films for HPP
Caner, Hernandez & Pascall, 2000; Caner, Hernandez & Harte, 2004; Caner, Hernandez, Pascall, & Riemer, 2003; Caner, Hernandez, Pascall, Balasubramaniam, & Harte, 2004
High pressure processing Polymer based packaging
PE/PA/Al/PP;
PET/SiOx/PUR/PE-LD; PET/Al2O3/PUR/PE-LD; PET/PVDC/PA/PE-HD/PP; PE/PA/EVAL/PE; PE/PA/PE; PET/EVAC, PP; PET/SiOx/PE-LD; PP/PA/PP; PET/Al2O3/PE-LD; PET/PVDC/EVAC Met-PET/EVAC/PE-LLD;
PP; PE/PA/EVAL/PE;
Significant increase in O2, CO2 and WV permeability. Significant D-limonene sorption. Significant physical damage. Unsuitable for batch HPP food packaging (at 800 MPa, 10 min, 60 C) No significant absorption of D-limonene (at 800 MPa for 10 min, at 60 C)
PP/EVAL/PP; PP/EVAL26/PP PP/EVAL48/PP
O2 permeability is not altered significantly. Polymers structure is not significantly affected (400 and 800 MPa, 5 and 10 min, 40, and 75 C).
Lo´pez-Rubio et al., 2005
PP/EVAL/PP; PP-O/PVAL/PE; PET/Al/CPP;
No significant change in: O2, and WV permeability; tensile strength and heat seal strength (400e600 MPa, 5 and 10 min)
Masuda et al., 1992
PA/PE; PET/PVDC/PE; PA/PP/PE
No significant change in: O2 and WV permeability, tensile strength, heat-seal strength and laminations (at 200, 350 and 500 MPa for 30 min at ambient temp.)
Lambert et al., 2000
PA/PE/EVOH/PE; PA/PP/EVAL/PP; PE/PA/PE; PET/Al/PE;
Oxygen permeability was not affected (550 MPa for 55 C and 20 min)
Cruz et al., 2003
PE-LD/PE-HD/PE-LD;
Poor sealing properties and mechanical damage (550 MPa for 55 C and 20 min) Decrease in the permeation rate of p-cymene (25 min, at 23 C at 50 MPa)
Go¨tz & Weisser, 2002 (continued on next page)
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Table 1 (continued) Packaging material
Effect of processes
Reference
PE-LD/EVAC/VDC;
Significant migration of compounds from the plastic material. No significant changes in material structure (400 MPa, 10 min at 12 C)
Rivas-Ca nedo et al., 2009
PLA isomers (L, D and DL)
Glass transition temperature (Tg) decrease (350, 450 and 650 MPa for 15 min and 22e26 C). The melting temperature remained unaffected. Partial shift in crystallinity of L-isomer was detected (at 650 MPa) with significant drop in enthalpy
Ahmed, Varshney, Zhang, & Ramaswamy, 2009
No change in O2 permeability. No significant global migration. Hydroperoxides and carbonyl compounds (ketones and aldehydes) formation (<25 kGy)
Rojas De Gante & Pascat, 1990
PE pouch
No change in O2 and WV permeability (gama-photons, 60Co)
Pilette, 1990
PET/PVDC/PE (glycol modified laminate)
Decrease in O2 permeability (60Co)
Kim-Kang & Gilbert, 1991
Surlyn
No significant change in tensile strength, elongation, Young’s modulus, tear strength and heat seal strength (100 kGy)
Hoh & Cumberbatch, 1991
PE-LD; EVAC; PET/PE/EVAL/PE
Number of volatile compounds were produced after irradiation (5, 20 and 100 kGy), and increase with increasing irradiation dose. No significant changes were observed in O2, WV and CO2 permeability
Riganakos et al., 1999
PS; SAN; PS-HI; ABS; PBD
High resistance to radiation (1e100 kGy). PBD very easily undergoes both cross-linking and degradation. In the absence of stabilizers, the effect of irradiation on PS is negligible even at high doses. Antioxidants and stabilizers are crucial in PBD and BD-containing copolymers
Pentimalli et al., 2000
PE; PP; PS
Decreased elongation, crystallinity, and solubility. Increased mechanical strength (40 kGy)
Ozen & Floros, 2001
PE-LD; PA6-PA6.6, PET
Reduction in transmittance (up to 100 kGy) No significant changes (up to 100 kGy)
Moura et al., 2004
PE-LD/EBP
Good seal quality and high overall package performance (0e100 kGy)
Nho, Kim, & Kang, 2006
PS, PET, PE-LD, PP, EVAC, PA6; PVC
RPs formation depends on the absorbed dose, dose rate, atmosphere, temperature, time after irradiation and food stimulant (10e50 kGy with gamma or e-beam sources)
Paquette, 2004
PA/PVDC/EVAC; PE-LD; PET/PE/EVAL/PE
Volatile compounds generated (1 kGy). Permeability to O2, CO2, and WV were not significantly altered
Descheˆnes et al., 1995; Riganakos et al., 1999
PET/PET/PE-LLD;
Significant decrease of mechanical properties. OTR and WVTR were not significantly affected (8, 10 and 15 kGy) OTR increased by 25%. WVTR was not changed significantly. Melting peak temperature decreased by 3.9% (at 15 kGy). No significant effect on tensile strength
Mizani et al., 2009
Alkyl, allyl and polyenyl free radicals formation (115 kGy) Higher oxidative stability than PE-UHMW (115 kGy)
Oral et al., 2006
Ionizing radiation PE-LD; PP-O
BOPP/CPP
PE-UHMW PE-UHMW (aTPE)
K. Gali c et al. / Trends in Food Science & Technology 22 (2011) 127e137 Table 1 (continued ) BOPP; EVAC; PE-LD; PE-HD; PS; Ionomers
No significant changes in the permeability (O2 and CO2) and WV (5, 10 and 30 kGy). Mechanical properties (tensile strength, percentage elongation at break and Young’s modulus) remained unaffected (5 and 10 kGy). No changes in overall migration values. 30 kGy resulted in an increase in overall migration values of BOPP and decrease in PE-HD and Ionomer films. Tensile strength of PE-HD, BOPP and Ionomers decreased (at 30 kGy). Mechanical properties of PS and EVAC remained unaffected after radiation at 30 kGy
Goulas, Riganakos, Badeka, & Kontominas, 2002
PVC/PE-HD; PE-HD/PA6; PE-HD; PET; PS; PP
Some degradation for PE-HD mono- and di-films occur (>60 kGy). PET was the most radiation-resistant material. PS was slightly affected after 30 kGy. PP was severly degraded and became very brittle. Migration from PP increases at higher doses, while from PE-HD/PVC tended to decrease. Odour and taste transfer as well as discoloration were observed with most plastics, especially at higher doses
Goulas, Riganakos, & Kontominas, 2004
Increase in tensile strength and puncture resistance and no change in elongation (5.22 W)
Banerjee et al., 1996
Powerful effect on mould spores destruction (from 0.244 to 0.977 J/cm2)
Turtoi & Nicolau, 2007
Decrease or increase in elongation depending on exposure time (0e30 h)
Tsobkallo, Petrova, & Khagen, 1988
PE, PP; PB
Reduction in melting point, increase in solubility and decrease in intrinsic viscosity (0e30 h)
Lofquist & Haylock, 1975
PP-O; BOPA
Significant changes in the thermal properties. Tensile strength (24 h exposure, 4.3 mg/L of ozone) of PP-O decreased (75%), and in BOPA increased (30%)
Ozen & Floros, 2001
PE-LLD; BOPA
O2 permeability decreased considerably with increasing treatment time
Ultrasound Sodium caseinate; Whey protein concentrate
Intense light pulse Paper/PE
Ozone PE
Ultrapasteurization PET Pulsed electric field PET; glass
PE-HD; PE-LD
Container lids: PA/Al/PE-LD Cups: PS-HI/PVDC/PE-LD
Chemically stable
Solano-Lopez, Ji, & Alvarez, 2005
Effective at retarding degradations of flavour compounds, vitamin C, and colour of treated orange juice (35 kV/cm, 59 ms), due to high O2-barrier Relatively low O2 barrier property caused vitamin C and flavour compounds lost (35 kV/cm, 59 ms)
Ayhan et al., 2001
PEF (35 kV/cm, 94 ms) for the apple juice, and PEF and PEF þ heat (60 C, 30 s) for the apple cider did not affect their colour stability during storage (4, 22, and 37 C for 70 days)
Evrendilek et al., 2000
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atmosphere (70% O2, 20% CO2, and 10% N2), and stored at 1 C have shelf life extended from 12 to 28 days (Djenane, Sanchez-Escalante, Beltran, & Roncales, 2001). UV-light, usually used for sterilization of packages used in aseptic processing, is often combined with ozone treatment. Ozone mainly reacts with the surface of the polymers and causes modification of the surface properties of polymers such as polarity and surface tension due to the formation of oxygen containing functional groups and degradation of the polymer chains. Plastic films with low surface tension have poor adhesion properties. However, both UV and ozone treatment, significantly increased the surface tension and hydrophilicity of polymers such as PE, PP and PET, and improved their adhesion properties (Razumovskii & Zaikov, 1983). UV and UV/ozone treatment resulted in extensive oxidation of PET, a strong UV absorbing film (Hill, Karbashewski, Lin, Strobel, & Walzak, 1995). The effect of ozone on the mechanical properties of plastic films depends on the polymer and the treatment conditions such as ozone concentration and temperature. Thus, in the case of PP-O tensile strength decrease up to 75%, while of BOPA increase of about 30% after ozone treatment (Ozen & Floros, 2001). Barrier properties of polymers might also be affected from ozone exposure. Oxygen permeability of linear low-density polyethylene (PE-LLD) treated with ozone (4.3 mg/l) for 24 h decreased about 50% (Ozen & Floros, 2001). UV treated PE-LD produced lower amounts of oxidation products compared to PET; however, oxidation was still significantly higher than of the samples contacted with untreated PE-LD. Higher oxidation observed in samples contacted with PET was attributed to polar nature of PET that may accelerate the oxidation of the film surface during UV-treatment (Berends, 1996). Ultrasound is also used in processing lines to detect the leaks in packages and control the microbiological quality of several foodstuffs (Ahvenainen, Wirtanen, & MattilaSandholm, 1991). Ultrasound treatment of sodium caseinate edible films greatly improved tensile strength and puncture resistance of these films while water vapour permeability, elongation at break and moisture content of the films were not affected by this treatment (Banerjee, Chen, & Wu, 1996). Authors argued that formation of smaller particles and lipid droplets due to ultrasound processing caused greater interaction between molecules, consequently resulting higher strength films. There is no general requirement for packaging materials for all non-thermal processes. However, from the above examples, most characteristics of packaging materials required for the various non-thermal processes are related to the barrier properties of the packaging materials. This is due to the satisfaction of the primary functions of packaging systems: containment, protection, and preservation (Han, 2007). Changes that might take place in the properties of the packages after exposure to new processing techniques as well as possible foodepackage interaction (i.e., migration of additives, monomers etc.) still need further investigation.
The effects of novel processing on packaging materials and food-package material interactions with the food itself (e.g. migration) is the main objective of EU-funded Integrated Project “NovelQ”. The project is designed to stimulate incremental innovations in novel food processing and packaging. Modifications in the properties of the packaging materials due to exposure to these processes do not necessarily have negative implications. Some of these processes could be used to add desirable properties to the materials. Therefore, it is necessary to understand the effects of these new treatments, not only on food and packaging but also consequences of foodepackage interaction, which is critical in the development of new and safe food products. The term interaction encompasses the sum of all mass transports from the package into the product as well as mass transport in the opposite direction. Food shelf-life determination It is recognized that defining the shelf life of a food, especially under the aforementioned time constraints, is a difficult task. This is an area of intense research for food product development scientists. Study of the different deterioration mechanisms that occur in food systems and judicious interpretations of the results have lead to meaningful and objectively measurable ways of accessing food quality and determining shelf life. Proper application of chemical kinetic principles to food quality loss allows for efficiently designing appropriate shelf-life tests and maximizing the useful information that can be obtained from the resulting data. There are different types of product changes that can limit the shelf life of food. Essentially, the shelf life of a food, i.e., the period it will retain an acceptable level of eating quality from a safety and organoleptic point of view, depends on four main factors, namely formulation, processing, packaging and storage conditions. In today’s modern processing terminology these factors are addressed in the HAACP (Hazard Analysis Critical Control Point) concept, a comprehensive quality control-quality assurance methodology that aims to ensure both food safety and high quality. All four factors are critical but their relative importance depends on the perishability of the food. Generally, a perishable food (properly stored) has, under 14 days of shelf life limited in most cases by biochemical or microbial decay. With new aseptic technology and controlled atmosphere/modified atmosphere packaging (CAP/MAP) such foods may last up to 90 days. Formulation involves the selection of the most appropriate raw materials and functional ingredients that will increase the appeal and ensure safety and integrity of the food for its intended shelf life. With respect to shelf life, key factors include the moisture content, Aw, pH and the addition of microbial preservatives and antioxidants. Processing subjects the formulated materials and ingredients to conditions that are unfavourable or inhibitory to undesirable deteriorative
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reactions and promotive to desirable physical and chemical changes thus giving the food product its final form and characteristics (except in the relatively few cases where post processing aging is necessary, e.g. in wines and hard cheeses). Once the food leaves the processing stage its keeping properties and the extent to which it will retain its intended attributes is a function of the microenvironment in the package. The important parameters are gas composition (oxygen, carbon dioxide, inert gases, ethylene, etc.), the relative humidity (%RH), pressure or mechanical stresses, light and temperature. These parameters are dependent on both packaging and storage conditions (He & Hoseney, 1990). Depending on the product nature, various properties or quality indices must be experimentally followed as a function of time in order to evaluate the degradation of the product quality in terms of the sensory, the microbiological and the physicochemical properties (Labuza & Contreras-Medellin, 1982). In order to fully account for all the degradation criteria, a well planned experimental investigation and analysis must be adopted (Figs. 1 and 2). In these terms, a standard and comprehensive protocol using the accelerated shelf life testing (ASLT) method, have been outlined (Corradini & Peleg, 2007). The data analysis can at times be very cumbersome and confusing especially if the product nature is not fully understood. In general, the analysis is performed by following the variation of each quality index in time during storage and then comparing the measured value to a threshold, which is officially set by the standards or commonly accepted by the profession or the consumer. As such, the quality degradation of the product is judged by looking independently to the variations of the individual properties of the product during storage, with a particular attention to the rapidly varying properties. Proper application of chemical kinetic principles to food quality loss is essential for efficiently designing appropriate tests and analyzing the obtained results (Mizrahi, 2004; Singh & Cadwallader, 2004). Traditional methods for the determination of shelf life include storage of the product at different temperatures and determining spoilage by sensory evaluation or microbial count. This will involve the natural
Testing strategy Prototype development Challenge study Pilot line testing Accelerated shelf-life testing Scale-up line trial Confirmatory storage study Full line production marketplace
On-going shelf-life monitoring
Fig. 1. Shelf-life testing strategy at different product development stages.
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flora of the product, which may vary between batches. An experimental evaluation of the optimal packaging conditions (in terms of package and food properties) is usually avoided because it is time-consuming; instead, a rough estimation is generally made by means of empirical methods. Semiempirical kinetic models are often used to describe the change in quality of frozen foods, and an Arrhenius equation may be used to describe the effect of temperature on the rate constant. These models would facilitate the design of packages that provide products with desired quality attributes (Taoukis, Labuza, & Saguy, 1997, chap. 10, pp. 1e75). As an alternative to this latter methodology, the optimal packaging conditions can be determined by means of mathematical models able to predict the shelf life of the packed product. This approach was first introduced by Heiss (1958), and subsequently, many authors proposed different mathematical models in which the moisture sensitivity of the food and the package performances were combined differently (Fava, Limbo, & Piergiovanni, 2000). Legislation Two of the primary functions of packaging are to protect food from contamination and to preserve its integrity. This makes demands on the packaging material itself. The materials may contain substances that are capable of migration into the packaged food. In order to protect consumers against potential hazards from oral exposure of packaging substances, European Union (EU) legislation has five main instruments: Regulations, Directives, Decisions, Recommendations and Opinions. The safety of food packaging materials is therefore generally based on the lack of potential toxic substances (from toxicological data) and the absence of migration from such substances (migration testing). Within the European Union, food packages are regulated by Regulation (EC) 1935/2004 of the European Parliament and of the Council of 27 October 2004 on materials and articles intended to come into contact with food. EU Directive 2002/72/EC lays down limits with respect to the concentration of certain substances in packaging or of migrants in foodstuffs or corresponding food simulants. These regulations are based on the toxicological data of substances. EU Directive 2002/72/EC stipulates that a maximum of 10 mg/dm2 or 60 mg/kg of physiologically nonhazardous substances may transfer from the packaging to the foodstuff (global migration). EU legislation (Regulation (EC) 1935/2004) also contains general provisions on the safety of active and intelligent (A&I) packaging and sets the framework for the safety evaluation process. A new Regulation specific to A&I packaging, published in 2009 (Regulation (EC) 450/2009), sets down additional requirements in order to ensure their safe use and introduces an authorisation scheme for substances used for active and intelligent functions in food contact materials.
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Before product on market
Packaging Food: from row materials to processing, packaging, storage..
Identify what may cause the food to spoil or become unsafe: food and process related spoilage; storage conditions...
Material properties: ex.Barrier to: Gases, vapour, aroma...
Sensitivity parameters Decide which tests to use
Plan the shelf life study: Actual sampling dates; number of samples; test parameters...
Methods: Vacuum, MAP, active...etc.
Determine the shelf life Keep written records of everything used or done, as these can be helpful when interpreting results = Permanent company database
Once product on market
Continue to monitor shelf-life: Physicochemical; Microbiological; Sensory parameters
Fig. 2. General food shelf- life protocol.
Conclusions There is a wide range of materials and technologies used in food packaging. Many changes have taken place over the last twenty years regarding the packaging of food. Recent research developments indicate that food packaging will continue to evolve and respond to the increased consumer needs and demands. Any decision, which packaging shall be used for a certain food, should be proceed by specific laboratory tests. A well known procedure is the test concerning migration, qualitatively (overall migration) and quantitatively (specific migration) as well. What packaging have in common is to protect what they contain and to help to maintain health (active protection function). The term “safety” sums up a number of legislative requirements which are demanded upon packagings. In practice, a package is regarded “safe”, if it has successfully passed relevant tests to prove that it meets with all of these requirements. It must be noted that responsible manufacturers of interactive packaging materials are aware of food law and incorporate packaging materials only with preserving agents, which are in conformity with the food law. Active packaging will probably increase in European countries in the near future, particularly in small and medium-sized enterprises (SMEs) and exporting food companies. This is due to both the consumers’ preference for minimally processed and naturally preserved foods and the food industry’s eagerness to invest in product quality and safety. The best way to avoid possible negative consumer attitudes towards new
packaging techniques would be to incorporate an active absorber and/or emitter into the packaging film or into the label. Furthermore, effects of non-thermal processing on the packaging materials and effects of packaging materials on the quality of non-thermally processed foods during shelf-life need to be studied for the selection of optimal packaging materials and methods. The globalization of the food industry enforces international standards and compliance with multiple regulations. New technologies should also be examined for their effect on product quality and public health, and the results of these tests should be disclosed to the public.
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Abbreviations1 ABS: Acrylonitrile/butadiene/styrene. Al: Aluminium. BOPA: Biaxially oriented polyamide. BOPP: Biaxially oriented polypropylene. CPP: Cast polypropylene. EBP: Ethylene-1-butene copolymer. EVAC (EVA): Ethylene/vinyl acetate. EVAL (EVOH): Ethylene/vinyl alcohol. OS: Oxygen scavenging. OTR: Oxygen transmission rate.
1 Recommended abbreviations (ISO, 2001), and old abbreviations (in brackets).
K. Gali c et al. / Trends in Food Science & Technology 22 (2011) 127e137 PA: Polyamide (Nylon). PA-MXD6: Poly(m-xylylene adipamide). PB: Polybutene. PBD: Polybutadiene. PE: Polyethylene. PE-HD (HDPE): High density polyethylene. PE-LD (LDPE): Low density polyethylene. PE-LLD (LLDPE): Linear low density polyethylene. PE-LMD: Linear medium density polyethylene. PEN: Polyethylene naphtalate. PET: Poly(ethylene terephthalate). PET-A (A-PET; APET): Amorphous poly(ethylene terephthalate). PE-UHMW (aTPE) (UHMWPE): Ultra high molecular weight polyethylene, aetocopherol-doped.
PG: 1,2-propanediol. PLA: Polylactides. PP: Polypropylene. PP-O (OPP): Oriented polypropylene. PS: Polystyrene. PS-HI (HIPS): High-impact polystyrene. PUR (PU): Polyurethane. PVAL (PVOH): Poly(vinyl alcohol). PVC: Poly(vinyl chloride). PVDC: Poly(vinylidene chloride). RPs: Radiolysis products. SAN: Styreneeacrylonitrile. VDC: Vinylidene chloride. WVTR: Water vapour transmission rate.
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Review
The benefits of processing and packaging *, Mario Scetar and Kata Galic Mia Kurek University of Zagreb, Faculty of Food Technology and Biotechnology, Pierottijeva 6, 10000 Zagreb, Croatia (e-mail: [email protected]) Food processing and preservation are generic terms that cover all aspects of extending the shelf life of foods. A number of novel thermal and non-thermal processing methods are actively undergoing research and development. A key step that needs addressing is finding the best packaging materials for commodities which preserve the benefits of improved product quality imparted by preservation technologies.
Introduction Food is packaged for storage, preservation, and protection traditionally for a long time. These three are the basic functions of food packaging that are still required today for better maintenance of quality and handling of foods. However, following the evolution of modern society and lifestyle, the significance of several functions of packaging is also shifting from one aspect to another (Brody, Bugusu, Han, Sand, & McHugh, 2008). There is a trend of changes in the priority of these functions with time and social circumstances. The distribution of priority of each packaging function is highly dependent on the commodities and, therefore, the properties of packaged foods. The commercialization of a newly developed non-thermal processing system essentially requires deep research on the packaging material properties and the interactions between the packaging materials and non-thermally processed foods. The packaging for non-thermally processed foods may necessitate extra functions of packaging for successful commercialization. Packaging materials should have strong physical and mechanical resistance to the non-thermal * Corresponding author. 0924-2244/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2010.04.001
process mechanisms. Non-thermal processes do not utilize increased temperature to inactivate decomposing microorganisms and enzymes. This is the biggest advantage of non-thermal processes because this low-temperature pasteurization does not overcook food and/or degrade foods thermally (Min & Zhang, 2005). Furthermore, hurdle technology is the term often applied when foods are preserved by a combination of processes. In general, hurdle technology is now widely used for food design in making new products according to the needs of processors and con´ lvarez, 2007; Siripatrawan & Jantawat, 2008). sumers (A This low-temperature treatment widens the selection of packaging materials and system does not require high melting temperature for heat seal. These methods produce far less volatile odour of plastics, additives, and printing solvent. This is very beneficial to high-fat foods and frozen/refrigerated foods. Since some of these techniques might require the processing of foods inside their package, it is important to understand the interaction between the package and the process itself (Clough, 2001; Devlieghere, Vermeiren, & Debevere, 2004; Ozen & Floros, 2001). Proper selection and optimizing of packaging are of major importance to food manufacturers due to aspects such as economy, marketing, logistics, distribution (Lelieveld, 2007; Min & Zhang, 2005; Trienekens, Hagen, Beulensc, & Omta, 2003), environmental impact of the packaging as well as the consumer demands (Ba´na´ti, 2005). Food-package interaction The quality of the packaged food is directly related to the food and packaging material attributes (Cooksey, 2007; Lee, Yam, & Piergiovanni, 2008). Most food products deteriorate in quality due to mass transfer phenomena, such as moisture absorption, oxygen invasion, flavour loss, undesirable odour absorption, and the migration of packaging components into the food (Kester & Fennema, 1986; Sajilata, Savitha, Singhal, & Kanetkar, 2007). The phenomena can occur between the food product and the atmospheric environment, between the food and the packaging materials, or among the heterogeneous ingredients in the food product itself. Thus, the rate of transport of such reactants across the partial barrier of the package wall can become the limiting factor in shelf life (Giacin, 1995; Hotckiss, 1995). Non-thermal processing in sequence with packaging requires transfer of the food into the package by aseptic or
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other means under reduced or elevated oxygen. After packaging, non-thermal processing generally requires hermetic closure before processing and maintenance of hermetic closure throughout the process and distribution. Non-thermal process also may be conducted while in package prior to hermetic closure. Critical protective barrier properties of packaging materials must be preserved to prevent chemical, physical, or microbial degradation of contents after nonthermal processing. Therefore, it is necessary to understand the process parameters and mechanisms/kinetics of the non-thermal process and their effects on packaging material properties. Some examples will be given to illustrate the possible issues arising from novel trends in food processing and packaging. High-pressure technology involves different packaging considerations, based on whether a product is processed in-container or packaged after processing. The packaging material must be able to withstand the operating pressures, have good sealing properties, and the ability to prevent quality deterioration during the application of pressure. At least one interface of the package should be flexible enough to transmit the pressure. Thus, rigid metal, glass, or plastic containers cannot be used. Due to the fact that air or gases are very compressible under high pressure, the more the headspace, the bigger the deformation strains on the packaging materials. The presence of headspace must be kept as small as possible (Rastogi, Raghavarao, Balasubramaniam, Niranjan, & Knorr, 2007). To increase the shelf life of processed foods, the package must be designed with an adequate water vapour (WV) and/ or gases (O2, CO2, etc.) permeabilities. According to literature data laminates, such as, PP/EVAL/PP; PP-O/PVAL/ PE; PA/PE; PET/PVDC/PE; PA/PP/PE etc., (Table 1) show no significant changes in gas barrier properties (Lambert et al., 2000; Masuda, Saito, Iwanami, & Hirai, 1992). The effect of high-pressure processing (HPP) treatment on functional properties of packages showed, in some cases, significant loss of heat sealability (PA/PE; PE/PA/EVAL/PE; PET/PE/EVAL/PE) or increase of migration levels (PE-LD/EVAC/VDC), (Dobias, Voldrich, Marek, & Chuda´ckova´, 2004; Rivas-Ca nedo, Ferna´ndezGarcı´a, & Nu nez, 2009). Furthermore, delamination between PP and Al, in PE/PA/Al/PP laminate, was observed in meal-ready-to-eat pouches treated at 200 MPa and 90 C for 10 min (Schauwecker, Balasubramaniam, Sadler, Pascall, & Adhikari, 2002). The packaging materials for irradiation (Table 1) should be chemically stable under the radiation dose to prevent polymer degradation and low molecular weight hydrocarbons and halogenated polymers formation which can migrate into foods (Clough, 2001; Haji-Saeid, Sampa, & Chmielewski, 2007; Oral, Rowell, & Muratoglu, 2006; Pentimalli et al., 2000; Rojas De Gante & Pascat, 1990). Radiolysis products (RPs) formed upon irradiation of a polymer or adjuvant could migrate into food and affect odour, taste, and safety of the irradiated food. Radiation
does not generally affect all properties of a polymer to the same degree. Barrier properties (Table 1) of some monofilms (PE-HD, PE-LD, PS, BOPP) where not significantly changed by irradiation (Rojas De Gante & Pascat, 1990). As for the laminates, barrier properties either decrease, as in the case of BOPP/CPP and PET/PVDC/PE (Kim-Kang & Gilbert, 1991; Mizani, Sheikh, Ebrahimi, Gerami, & Tavakoli, 2009), or are not significantly affected, ex. PA/PVDC/EVAC, PET/PE/EVAL/PE and PET/ PET/PE-LLD (Descheˆnes et al., 1995; Mizani et al., 2009; Riganakos, Koller, Ehlermann, Bauer, & Kontominas, 1999), with applied radiation doses. Modified atmosphere packaging (MAP) has been intensively investigated to minimize quality changes of irradiated foods during storage. However, an attention needs to be drawn in applying MAP for the packaging of non-thermally processed foods since MAP can selectively change the microbiology of foods. The suppression of aerobic spoilage microorganisms will decrease competition for growth and provide sufficient time for the growth of pathogenic microorganisms, especially if the MAP foods received a nonsterilizing treatment (Hotchkiss & Banco, 1992). Aseptic packaging is considered the most appropriate way of packaging for pulsed electric fields (PEF) processed foods. Traditional methods for juice packaging aim to reduce the exposure of the juice to oxygen through the use of high barrier materials such as glass or foil laminates in brick packs, with or without nitrogen flushing or improving gas barrier of PET by blending with aromatic polyamides (Hu et al., 2005). The use of oxygen scavengers with an appropriate packaging material can further reduce the presence of dissolved oxygen in the juice or present initially in the headspace (Ros-Chumillas, Belissario, Iguaz, & Lo´pez, 2007; Zerdin, Rooney, & Vermue¨, 2003). Unlike glass and PET, PE-HD and PE-LD bottles were not effective at retarding degradations of flavour compounds and vitamin C of PEF-treated orange juice during storage at 4 C for 112 days, which might be due to their relatively low barrier property of polyethylene to oxygen (Ayhan, Yeom, Zhang, & Min, 2001). The degradation of lycopene of PEF-processed tomato juice in a PP tube was found most significant during the first seven days of the storage at 4 C (Min, Jin, & Zhang, 2003). The main cause of carotenoid degradation in foods is oxidation (Thakur, Singh, & Nelson, 1996), and thus the significant reduction was considered due to oxygen availability in the headspace of the PP tubes (Min et al., 2003). The MAP, which limits oxygen in the headspace, may be applied as a complement to PEF to reduce oxidation of PEF-processed food products. For pulsed UV/white-light emission process, the packaging material must be transparent during pulsed light emission. Due to poor penetrative properties, UV light is more or less limited to surface applications, but it shows promise as a post-packaging treatment. For example UV irradiated beef steak, packaged in PE pouches with modified
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Table 1. Effects of new processing techniques on the packaging material properties Packaging material
Effect of processes
Reference
Barrier properties and structural characteristics of material were not affected (400 MPa, for 30 min at 25 C)
Nachamansion, 1995
PE/PA/EVAL/PE; PET/PE/EVAL/PE; PE-LD/PA/PE-LD; PE-LD/PE-LLD; PPantifog; BOPP; PA/PE; PE-LD/EVAL/PE-LD/PETA/expPET/PET-A;
Loss of heat sealability, increased migration levels (600 MPa for 60 min, at room temperature). Further confirmation needed
Dobias et al., 2004
PET/PA/Al/PP PA/EVAL/PE
No detectable PG migration PG migration was similar at 30, 50, and 75 C after 10 min. under atmospheric pressure. PG migration into the PA/EVAL/PE significantly decreased when treated with high pressure (200, 400, 690 and 827 MPa) at 30, 50, and 75 C At 75, and 50 C, the PG migration was significantly higher than the amounts detected at 30 C. Visible signs of delamination between the PP and Al layers (at200 MPa and 90 C for 10 min)
Schauwecker et al., 2002
The increase in permeance was less than 11%. No significant changes in tensile strength, elongation and modulus of elasticity (600e800 MPa for 5,10 and 20 min at 45 C). Prolonged exposure had a greater effect on the permeance of inorganic layers in some films, than lower pressure/time combinations. Mechanical analysis is not a good analytical approach to determine the suitability of films for HPP
Caner, Hernandez & Pascall, 2000; Caner, Hernandez & Harte, 2004; Caner, Hernandez, Pascall, & Riemer, 2003; Caner, Hernandez, Pascall, Balasubramaniam, & Harte, 2004
High pressure processing Polymer based packaging
PE/PA/Al/PP;
PET/SiOx/PUR/PE-LD; PET/Al2O3/PUR/PE-LD; PET/PVDC/PA/PE-HD/PP; PE/PA/EVAL/PE; PE/PA/PE; PET/EVAC, PP; PET/SiOx/PE-LD; PP/PA/PP; PET/Al2O3/PE-LD; PET/PVDC/EVAC Met-PET/EVAC/PE-LLD;
PP; PE/PA/EVAL/PE;
Significant increase in O2, CO2 and WV permeability. Significant D-limonene sorption. Significant physical damage. Unsuitable for batch HPP food packaging (at 800 MPa, 10 min, 60 C) No significant absorption of D-limonene (at 800 MPa for 10 min, at 60 C)
PP/EVAL/PP; PP/EVAL26/PP PP/EVAL48/PP
O2 permeability is not altered significantly. Polymers structure is not significantly affected (400 and 800 MPa, 5 and 10 min, 40, and 75 C).
Lo´pez-Rubio et al., 2005
PP/EVAL/PP; PP-O/PVAL/PE; PET/Al/CPP;
No significant change in: O2, and WV permeability; tensile strength and heat seal strength (400e600 MPa, 5 and 10 min)
Masuda et al., 1992
PA/PE; PET/PVDC/PE; PA/PP/PE
No significant change in: O2 and WV permeability, tensile strength, heat-seal strength and laminations (at 200, 350 and 500 MPa for 30 min at ambient temp.)
Lambert et al., 2000
PA/PE/EVOH/PE; PA/PP/EVAL/PP; PE/PA/PE; PET/Al/PE;
Oxygen permeability was not affected (550 MPa for 55 C and 20 min)
Cruz et al., 2003
PE-LD/PE-HD/PE-LD;
Poor sealing properties and mechanical damage (550 MPa for 55 C and 20 min) Decrease in the permeation rate of p-cymene (25 min, at 23 C at 50 MPa)
Go¨tz & Weisser, 2002 (continued on next page)
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Table 1 (continued) Packaging material
Effect of processes
Reference
PE-LD/EVAC/VDC;
Significant migration of compounds from the plastic material. No significant changes in material structure (400 MPa, 10 min at 12 C)
Rivas-Ca nedo et al., 2009
PLA isomers (L, D and DL)
Glass transition temperature (Tg) decrease (350, 450 and 650 MPa for 15 min and 22e26 C). The melting temperature remained unaffected. Partial shift in crystallinity of L-isomer was detected (at 650 MPa) with significant drop in enthalpy
Ahmed, Varshney, Zhang, & Ramaswamy, 2009
No change in O2 permeability. No significant global migration. Hydroperoxides and carbonyl compounds (ketones and aldehydes) formation (<25 kGy)
Rojas De Gante & Pascat, 1990
PE pouch
No change in O2 and WV permeability (gama-photons, 60Co)
Pilette, 1990
PET/PVDC/PE (glycol modified laminate)
Decrease in O2 permeability (60Co)
Kim-Kang & Gilbert, 1991
Surlyn
No significant change in tensile strength, elongation, Young’s modulus, tear strength and heat seal strength (100 kGy)
Hoh & Cumberbatch, 1991
PE-LD; EVAC; PET/PE/EVAL/PE
Number of volatile compounds were produced after irradiation (5, 20 and 100 kGy), and increase with increasing irradiation dose. No significant changes were observed in O2, WV and CO2 permeability
Riganakos et al., 1999
PS; SAN; PS-HI; ABS; PBD
High resistance to radiation (1e100 kGy). PBD very easily undergoes both cross-linking and degradation. In the absence of stabilizers, the effect of irradiation on PS is negligible even at high doses. Antioxidants and stabilizers are crucial in PBD and BD-containing copolymers
Pentimalli et al., 2000
PE; PP; PS
Decreased elongation, crystallinity, and solubility. Increased mechanical strength (40 kGy)
Ozen & Floros, 2001
PE-LD; PA6-PA6.6, PET
Reduction in transmittance (up to 100 kGy) No significant changes (up to 100 kGy)
Moura et al., 2004
PE-LD/EBP
Good seal quality and high overall package performance (0e100 kGy)
Nho, Kim, & Kang, 2006
PS, PET, PE-LD, PP, EVAC, PA6; PVC
RPs formation depends on the absorbed dose, dose rate, atmosphere, temperature, time after irradiation and food stimulant (10e50 kGy with gamma or e-beam sources)
Paquette, 2004
PA/PVDC/EVAC; PE-LD; PET/PE/EVAL/PE
Volatile compounds generated (1 kGy). Permeability to O2, CO2, and WV were not significantly altered
Descheˆnes et al., 1995; Riganakos et al., 1999
PET/PET/PE-LLD;
Significant decrease of mechanical properties. OTR and WVTR were not significantly affected (8, 10 and 15 kGy) OTR increased by 25%. WVTR was not changed significantly. Melting peak temperature decreased by 3.9% (at 15 kGy). No significant effect on tensile strength
Mizani et al., 2009
Alkyl, allyl and polyenyl free radicals formation (115 kGy) Higher oxidative stability than PE-UHMW (115 kGy)
Oral et al., 2006
Ionizing radiation PE-LD; PP-O
BOPP/CPP
PE-UHMW PE-UHMW (aTPE)
K. Gali c et al. / Trends in Food Science & Technology 22 (2011) 127e137 Table 1 (continued ) BOPP; EVAC; PE-LD; PE-HD; PS; Ionomers
No significant changes in the permeability (O2 and CO2) and WV (5, 10 and 30 kGy). Mechanical properties (tensile strength, percentage elongation at break and Young’s modulus) remained unaffected (5 and 10 kGy). No changes in overall migration values. 30 kGy resulted in an increase in overall migration values of BOPP and decrease in PE-HD and Ionomer films. Tensile strength of PE-HD, BOPP and Ionomers decreased (at 30 kGy). Mechanical properties of PS and EVAC remained unaffected after radiation at 30 kGy
Goulas, Riganakos, Badeka, & Kontominas, 2002
PVC/PE-HD; PE-HD/PA6; PE-HD; PET; PS; PP
Some degradation for PE-HD mono- and di-films occur (>60 kGy). PET was the most radiation-resistant material. PS was slightly affected after 30 kGy. PP was severly degraded and became very brittle. Migration from PP increases at higher doses, while from PE-HD/PVC tended to decrease. Odour and taste transfer as well as discoloration were observed with most plastics, especially at higher doses
Goulas, Riganakos, & Kontominas, 2004
Increase in tensile strength and puncture resistance and no change in elongation (5.22 W)
Banerjee et al., 1996
Powerful effect on mould spores destruction (from 0.244 to 0.977 J/cm2)
Turtoi & Nicolau, 2007
Decrease or increase in elongation depending on exposure time (0e30 h)
Tsobkallo, Petrova, & Khagen, 1988
PE, PP; PB
Reduction in melting point, increase in solubility and decrease in intrinsic viscosity (0e30 h)
Lofquist & Haylock, 1975
PP-O; BOPA
Significant changes in the thermal properties. Tensile strength (24 h exposure, 4.3 mg/L of ozone) of PP-O decreased (75%), and in BOPA increased (30%)
Ozen & Floros, 2001
PE-LLD; BOPA
O2 permeability decreased considerably with increasing treatment time
Ultrasound Sodium caseinate; Whey protein concentrate
Intense light pulse Paper/PE
Ozone PE
Ultrapasteurization PET Pulsed electric field PET; glass
PE-HD; PE-LD
Container lids: PA/Al/PE-LD Cups: PS-HI/PVDC/PE-LD
Chemically stable
Solano-Lopez, Ji, & Alvarez, 2005
Effective at retarding degradations of flavour compounds, vitamin C, and colour of treated orange juice (35 kV/cm, 59 ms), due to high O2-barrier Relatively low O2 barrier property caused vitamin C and flavour compounds lost (35 kV/cm, 59 ms)
Ayhan et al., 2001
PEF (35 kV/cm, 94 ms) for the apple juice, and PEF and PEF þ heat (60 C, 30 s) for the apple cider did not affect their colour stability during storage (4, 22, and 37 C for 70 days)
Evrendilek et al., 2000
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atmosphere (70% O2, 20% CO2, and 10% N2), and stored at 1 C have shelf life extended from 12 to 28 days (Djenane, Sanchez-Escalante, Beltran, & Roncales, 2001). UV-light, usually used for sterilization of packages used in aseptic processing, is often combined with ozone treatment. Ozone mainly reacts with the surface of the polymers and causes modification of the surface properties of polymers such as polarity and surface tension due to the formation of oxygen containing functional groups and degradation of the polymer chains. Plastic films with low surface tension have poor adhesion properties. However, both UV and ozone treatment, significantly increased the surface tension and hydrophilicity of polymers such as PE, PP and PET, and improved their adhesion properties (Razumovskii & Zaikov, 1983). UV and UV/ozone treatment resulted in extensive oxidation of PET, a strong UV absorbing film (Hill, Karbashewski, Lin, Strobel, & Walzak, 1995). The effect of ozone on the mechanical properties of plastic films depends on the polymer and the treatment conditions such as ozone concentration and temperature. Thus, in the case of PP-O tensile strength decrease up to 75%, while of BOPA increase of about 30% after ozone treatment (Ozen & Floros, 2001). Barrier properties of polymers might also be affected from ozone exposure. Oxygen permeability of linear low-density polyethylene (PE-LLD) treated with ozone (4.3 mg/l) for 24 h decreased about 50% (Ozen & Floros, 2001). UV treated PE-LD produced lower amounts of oxidation products compared to PET; however, oxidation was still significantly higher than of the samples contacted with untreated PE-LD. Higher oxidation observed in samples contacted with PET was attributed to polar nature of PET that may accelerate the oxidation of the film surface during UV-treatment (Berends, 1996). Ultrasound is also used in processing lines to detect the leaks in packages and control the microbiological quality of several foodstuffs (Ahvenainen, Wirtanen, & MattilaSandholm, 1991). Ultrasound treatment of sodium caseinate edible films greatly improved tensile strength and puncture resistance of these films while water vapour permeability, elongation at break and moisture content of the films were not affected by this treatment (Banerjee, Chen, & Wu, 1996). Authors argued that formation of smaller particles and lipid droplets due to ultrasound processing caused greater interaction between molecules, consequently resulting higher strength films. There is no general requirement for packaging materials for all non-thermal processes. However, from the above examples, most characteristics of packaging materials required for the various non-thermal processes are related to the barrier properties of the packaging materials. This is due to the satisfaction of the primary functions of packaging systems: containment, protection, and preservation (Han, 2007). Changes that might take place in the properties of the packages after exposure to new processing techniques as well as possible foodepackage interaction (i.e., migration of additives, monomers etc.) still need further investigation.
The effects of novel processing on packaging materials and food-package material interactions with the food itself (e.g. migration) is the main objective of EU-funded Integrated Project “NovelQ”. The project is designed to stimulate incremental innovations in novel food processing and packaging. Modifications in the properties of the packaging materials due to exposure to these processes do not necessarily have negative implications. Some of these processes could be used to add desirable properties to the materials. Therefore, it is necessary to understand the effects of these new treatments, not only on food and packaging but also consequences of foodepackage interaction, which is critical in the development of new and safe food products. The term interaction encompasses the sum of all mass transports from the package into the product as well as mass transport in the opposite direction. Food shelf-life determination It is recognized that defining the shelf life of a food, especially under the aforementioned time constraints, is a difficult task. This is an area of intense research for food product development scientists. Study of the different deterioration mechanisms that occur in food systems and judicious interpretations of the results have lead to meaningful and objectively measurable ways of accessing food quality and determining shelf life. Proper application of chemical kinetic principles to food quality loss allows for efficiently designing appropriate shelf-life tests and maximizing the useful information that can be obtained from the resulting data. There are different types of product changes that can limit the shelf life of food. Essentially, the shelf life of a food, i.e., the period it will retain an acceptable level of eating quality from a safety and organoleptic point of view, depends on four main factors, namely formulation, processing, packaging and storage conditions. In today’s modern processing terminology these factors are addressed in the HAACP (Hazard Analysis Critical Control Point) concept, a comprehensive quality control-quality assurance methodology that aims to ensure both food safety and high quality. All four factors are critical but their relative importance depends on the perishability of the food. Generally, a perishable food (properly stored) has, under 14 days of shelf life limited in most cases by biochemical or microbial decay. With new aseptic technology and controlled atmosphere/modified atmosphere packaging (CAP/MAP) such foods may last up to 90 days. Formulation involves the selection of the most appropriate raw materials and functional ingredients that will increase the appeal and ensure safety and integrity of the food for its intended shelf life. With respect to shelf life, key factors include the moisture content, Aw, pH and the addition of microbial preservatives and antioxidants. Processing subjects the formulated materials and ingredients to conditions that are unfavourable or inhibitory to undesirable deteriorative
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reactions and promotive to desirable physical and chemical changes thus giving the food product its final form and characteristics (except in the relatively few cases where post processing aging is necessary, e.g. in wines and hard cheeses). Once the food leaves the processing stage its keeping properties and the extent to which it will retain its intended attributes is a function of the microenvironment in the package. The important parameters are gas composition (oxygen, carbon dioxide, inert gases, ethylene, etc.), the relative humidity (%RH), pressure or mechanical stresses, light and temperature. These parameters are dependent on both packaging and storage conditions (He & Hoseney, 1990). Depending on the product nature, various properties or quality indices must be experimentally followed as a function of time in order to evaluate the degradation of the product quality in terms of the sensory, the microbiological and the physicochemical properties (Labuza & Contreras-Medellin, 1982). In order to fully account for all the degradation criteria, a well planned experimental investigation and analysis must be adopted (Figs. 1 and 2). In these terms, a standard and comprehensive protocol using the accelerated shelf life testing (ASLT) method, have been outlined (Corradini & Peleg, 2007). The data analysis can at times be very cumbersome and confusing especially if the product nature is not fully understood. In general, the analysis is performed by following the variation of each quality index in time during storage and then comparing the measured value to a threshold, which is officially set by the standards or commonly accepted by the profession or the consumer. As such, the quality degradation of the product is judged by looking independently to the variations of the individual properties of the product during storage, with a particular attention to the rapidly varying properties. Proper application of chemical kinetic principles to food quality loss is essential for efficiently designing appropriate tests and analyzing the obtained results (Mizrahi, 2004; Singh & Cadwallader, 2004). Traditional methods for the determination of shelf life include storage of the product at different temperatures and determining spoilage by sensory evaluation or microbial count. This will involve the natural
Testing strategy Prototype development Challenge study Pilot line testing Accelerated shelf-life testing Scale-up line trial Confirmatory storage study Full line production marketplace
On-going shelf-life monitoring
Fig. 1. Shelf-life testing strategy at different product development stages.
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flora of the product, which may vary between batches. An experimental evaluation of the optimal packaging conditions (in terms of package and food properties) is usually avoided because it is time-consuming; instead, a rough estimation is generally made by means of empirical methods. Semiempirical kinetic models are often used to describe the change in quality of frozen foods, and an Arrhenius equation may be used to describe the effect of temperature on the rate constant. These models would facilitate the design of packages that provide products with desired quality attributes (Taoukis, Labuza, & Saguy, 1997, chap. 10, pp. 1e75). As an alternative to this latter methodology, the optimal packaging conditions can be determined by means of mathematical models able to predict the shelf life of the packed product. This approach was first introduced by Heiss (1958), and subsequently, many authors proposed different mathematical models in which the moisture sensitivity of the food and the package performances were combined differently (Fava, Limbo, & Piergiovanni, 2000). Legislation Two of the primary functions of packaging are to protect food from contamination and to preserve its integrity. This makes demands on the packaging material itself. The materials may contain substances that are capable of migration into the packaged food. In order to protect consumers against potential hazards from oral exposure of packaging substances, European Union (EU) legislation has five main instruments: Regulations, Directives, Decisions, Recommendations and Opinions. The safety of food packaging materials is therefore generally based on the lack of potential toxic substances (from toxicological data) and the absence of migration from such substances (migration testing). Within the European Union, food packages are regulated by Regulation (EC) 1935/2004 of the European Parliament and of the Council of 27 October 2004 on materials and articles intended to come into contact with food. EU Directive 2002/72/EC lays down limits with respect to the concentration of certain substances in packaging or of migrants in foodstuffs or corresponding food simulants. These regulations are based on the toxicological data of substances. EU Directive 2002/72/EC stipulates that a maximum of 10 mg/dm2 or 60 mg/kg of physiologically nonhazardous substances may transfer from the packaging to the foodstuff (global migration). EU legislation (Regulation (EC) 1935/2004) also contains general provisions on the safety of active and intelligent (A&I) packaging and sets the framework for the safety evaluation process. A new Regulation specific to A&I packaging, published in 2009 (Regulation (EC) 450/2009), sets down additional requirements in order to ensure their safe use and introduces an authorisation scheme for substances used for active and intelligent functions in food contact materials.
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Before product on market
Packaging Food: from row materials to processing, packaging, storage..
Identify what may cause the food to spoil or become unsafe: food and process related spoilage; storage conditions...
Material properties: ex.Barrier to: Gases, vapour, aroma...
Sensitivity parameters Decide which tests to use
Plan the shelf life study: Actual sampling dates; number of samples; test parameters...
Methods: Vacuum, MAP, active...etc.
Determine the shelf life Keep written records of everything used or done, as these can be helpful when interpreting results = Permanent company database
Once product on market
Continue to monitor shelf-life: Physicochemical; Microbiological; Sensory parameters
Fig. 2. General food shelf- life protocol.
Conclusions There is a wide range of materials and technologies used in food packaging. Many changes have taken place over the last twenty years regarding the packaging of food. Recent research developments indicate that food packaging will continue to evolve and respond to the increased consumer needs and demands. Any decision, which packaging shall be used for a certain food, should be proceed by specific laboratory tests. A well known procedure is the test concerning migration, qualitatively (overall migration) and quantitatively (specific migration) as well. What packaging have in common is to protect what they contain and to help to maintain health (active protection function). The term “safety” sums up a number of legislative requirements which are demanded upon packagings. In practice, a package is regarded “safe”, if it has successfully passed relevant tests to prove that it meets with all of these requirements. It must be noted that responsible manufacturers of interactive packaging materials are aware of food law and incorporate packaging materials only with preserving agents, which are in conformity with the food law. Active packaging will probably increase in European countries in the near future, particularly in small and medium-sized enterprises (SMEs) and exporting food companies. This is due to both the consumers’ preference for minimally processed and naturally preserved foods and the food industry’s eagerness to invest in product quality and safety. The best way to avoid possible negative consumer attitudes towards new
packaging techniques would be to incorporate an active absorber and/or emitter into the packaging film or into the label. Furthermore, effects of non-thermal processing on the packaging materials and effects of packaging materials on the quality of non-thermally processed foods during shelf-life need to be studied for the selection of optimal packaging materials and methods. The globalization of the food industry enforces international standards and compliance with multiple regulations. New technologies should also be examined for their effect on product quality and public health, and the results of these tests should be disclosed to the public.
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Abbreviations1 ABS: Acrylonitrile/butadiene/styrene. Al: Aluminium. BOPA: Biaxially oriented polyamide. BOPP: Biaxially oriented polypropylene. CPP: Cast polypropylene. EBP: Ethylene-1-butene copolymer. EVAC (EVA): Ethylene/vinyl acetate. EVAL (EVOH): Ethylene/vinyl alcohol. OS: Oxygen scavenging. OTR: Oxygen transmission rate.
1 Recommended abbreviations (ISO, 2001), and old abbreviations (in brackets).
K. Gali c et al. / Trends in Food Science & Technology 22 (2011) 127e137 PA: Polyamide (Nylon). PA-MXD6: Poly(m-xylylene adipamide). PB: Polybutene. PBD: Polybutadiene. PE: Polyethylene. PE-HD (HDPE): High density polyethylene. PE-LD (LDPE): Low density polyethylene. PE-LLD (LLDPE): Linear low density polyethylene. PE-LMD: Linear medium density polyethylene. PEN: Polyethylene naphtalate. PET: Poly(ethylene terephthalate). PET-A (A-PET; APET): Amorphous poly(ethylene terephthalate). PE-UHMW (aTPE) (UHMWPE): Ultra high molecular weight polyethylene, aetocopherol-doped.
PG: 1,2-propanediol. PLA: Polylactides. PP: Polypropylene. PP-O (OPP): Oriented polypropylene. PS: Polystyrene. PS-HI (HIPS): High-impact polystyrene. PUR (PU): Polyurethane. PVAL (PVOH): Poly(vinyl alcohol). PVC: Poly(vinyl chloride). PVDC: Poly(vinylidene chloride). RPs: Radiolysis products. SAN: Styreneeacrylonitrile. VDC: Vinylidene chloride. WVTR: Water vapour transmission rate.
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