Design of Biodegradable Bio-Based Equilibrium Modified Atmosphere
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Postharvest Biology and Technology 111 (2016) 380–389 Contents lists available at ScienceDirect Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio Design of biodegradable bio-based equilibrium modified atmosphere packaging (EMAP) for fresh fruits and vegetables by using micro-perforated poly-lactic acid (PLA) films a, a a Antonis Mistriotis *, Demetrios Briassoulis , Anastasios Giannoulis , b Salvatore D’Aquino a Agricultural University of Athens, Laboratory of Agricultural Structures, 75 Iera Odos, Athens, 11855 Greece b National Council of Reserch of Italy—Institute of Sciences of Food Production (ISPA-CNR), Traversa La Crucca, 3, loc. Baldinca, Li Punti - 07100 Sassari, Italy A R T I C L E I N F O A B S T R A C T Article history: Equilibrium modified atmosphere packaging (EMAP) is used for prolonging the shelf life of fresh produce Received 12 February 2015 such as fruits and vegetables and preserving their quality characteristics such as freshness, colour and Received in revised form 3 September 2015 aroma. However, the resulting extensive use of plastic packaging films raises serious environmental Accepted 14 September 2015 concerns. Replacing conventional plastic films with novel biobased and biodegradable under composting conditions materials such as films made of poly-lactic acid (PLA), offers new sustainable solutions to the Keywords: problem. In the present work, the gas transport properties of three layer PLA films have been studied in EMAP relation to their potential as EMA packaging materials for fresh produce. A simple one-dimensional PLA film model simulating the combined gas diffusion through micro-perforations and the permeable membrane Gas diffusion Micro-perforation was developed as a designing tool for PLA based EMA packaging systems. By using this model, innovative fi Horticultural produce packaging biodegradable bio-based EMAP systems were designed speci cally for selected fruits and vegetables fi Bio-based materials using laser microperforated, water vapour (WV) permeable PLA lms. It was shown that the relatively Bio-based packaging high water vapour permeability of PLA films compared to conventional OPP films allows the development of an optimised biodegradable bio-based EMA packaging for the specific applications. ã 2015 Elsevier B.V. All rights reserved. 1. Introduction the temperature increases O2 requirements from tissues increase too, while tolerance to CO2 decreases (Kader, 1997). Fruits and vegetables are two of the main agricultural product The main disadvantage of EMAP, like any other conventional categories in Europe. Packaging is particularly important for food packaging, is the extensive use of plastic films resulting into exported fruits as it allows preserving their quality and health huge quantities of domestic plastic wastes. Global plastic film and safety and facilitates labelling of the produce. Recently, advanced sheets market is expected to reach 70.9 million tons by 2018 techniques such as equilibrium modified atmosphere packaging (Markets and Markets, 2014). A large percentage of this quantity is (EMAP) for dynamically modifying the in-package atmosphere are used for food packaging. Although recycling of these materials used for extending the shelf life of high value fresh produce increased during the last decade, only a small part of the generated (Sandhya, 2010). amount of plastic waste is finally recycled (Themelis et al., 2011). Successful applications of EMAP include a wide variety of Therefore replacing non-degradable conventional plastics based produce, such as broccoli florets, cauliflower florets, carrots, baby on fossil oil with sustainable bio-based biodegradable materials is carrots, peeled garlic (Lee et al., 1996). However, most of the of great environmental importance. Various bio-based plastics published studies for recommended CO2 and O2 concentrations have been studied already as possible alternatives to conventional generally represent the conditions in the temperatures range of 0– packaging materials (Siracusa, 2008). 5 C that maximize the storage life of each commodity (Fernández- Such a promising biodegradable plastic material is poly-lactic Trujilio et al., 1988; Malakou and Nanos, 2005; Irtwange, 2006). As acid (PLA). PLA was introduced as a packaging material and started being produced at a commercial level about ten years ago. It has attracted attention mostly because of its sustainable nature: it is * Corresponding author. Fax: +30 2105294023. synthesized from processed corn or other naturally produced E-mail address: [email protected] (A. Mistriotis). http://dx.doi.org/10.1016/j.postharvbio.2015.09.022 0925-5214/ã 2015 Elsevier B.V. All rights reserved. A. Mistriotis et al. / Postharvest Biology and Technology 111 (2016) 380–389 381 carbohydrates, thus it is a bio-based material, and it biodegrades contribute to a longer shelf-life of the packaged produce (Almenar after use under industrial composting conditions (Auras et al., et al., 2008; Briassoulis et al., 2013). 2004). The main objective of the present work was the development of a one-dimensional steady state analytical model of the in-package PLA can be used for the development of transparent thin films atmosphere assuming that WV transport process through the suitable for food packaging (Auras et al., 2004). PLA’s certified permeable packaging film obeys Fick’s law. Using this analytical compostability and compliance with the food contact safety model, packaging bags made of PLA have been optimally designed regulations (Auras et al., 2004) makes it attractive as packaging and developed for two selected horticultural produce: cherry material, since it meets the compostability requirements of tomatoes and peach, as typical high value vegetables and fruits EN13432 for packaging (EN 13.432, 2005), thus alleviating the respectively. These optimized packaging systems were tested plastic wastes problem. PLA exhibits high water vapour (WV) through full-scale experiments to confirm the validity of the design permeability compared to conventional plastic packaging films, methodology. while its permeability to CO2 and O2 is comparable. The performance of an EMA packaging greatly depends on its 2. Materials and methods optimised design which has to be tailored to the needs of the specific packaged produce. Gases are exchanged between the 2.1. Definitions and terminology package and the environment by a restricted diffusion process resulting into an EMA in the package. In a typical EMAP the Before presenting the relevant methodology and the results of synthesis of the in-package atmosphere is controlled by selecting the present work, it is important to clarify the definitions related to the gas transport properties of the packaging film. The equilibrium the diffusive gas transport through membranes in order to avoid (steady state) modified atmosphere (EMA) is obtained when the confusions, as the relevant terminology is not unique in the exchange rate of gases through the covering film is in equilibrium literature. The gas barrier property of a material is expressed by its with the production or consumption of gases at the respiring and À2 À1 À1 gas mass permeability P (kg m m s Pa ). This is defined as the transpiring produce. Therefore, the gas transport properties of the gas mass (kg) which, under steady conditions, crosses unit area fi packaging system have to be designed to meet the speci c 2 (m ) and unit thickness (m) of the specimen, in unit time (s) under requirements of the packaged produce. A technique for adjusting unit pressure difference (Pa) and at constant temperature. In the gas transport properties of a packaging film is perforation. Both particular, the permeability of a plate or membrane is expressed by macro-perforation by mechanical means (Van der Steen et al., the one-dimensional Fick’s law of diffusion as: 2002) and laser made micro-perforation (Ozdemir et al., 2005) are used for this purpose. In the case of a perforated film, the diffusion dp F ¼ À P A ð1Þ is not spatially uniform and the combined transmission effect of dx both perforations and film has to be investigated. The size and the À1 where F (kg s ) is the mass flow rate of the gas, dp=dxis the number of perforations have to be estimated to meet the specific À1 gradient of the gas pressure across the specimen (Pa m ) and A needs of the packaged fruits or vegetables for a given packaging 2 (m ) is the area of the membrane. If a gas mixture is considered, gas configuration. For this reason, the development of a model pressure, p (Pa) refers to the partial pressure of a gas in the mixture, predicting the gas transfer through a perforated film is a necessary thus it is a measure of the molar fraction, c, of the gas in the tool for designing the perforation pattern. Such a model has to take mixture. into account the combined gas transport through both the In the case of a gas mixture, the partial pressure gradient can packaging film and the perforations (Paul and Clarke, 2002; also be expressed as the molar fraction gradient of the gas, Rennie and Tavoularis, 2009; Briassoulis et al., 2013). À1 dc=dx(m ). Then the mass permeability is expressed in (kg m Several attempts have been made to model gas transfer through À2 À1 2 À1 m s ) and the volume permeability in m s . a perforated permeable film for optimizing EMAP (Paul and Clark, When a thin film is considered, its gas transfer characteristics 2002; Rennie and Tavoularis, 2009). These models focus on the gas are described by the permeance, PR. In the Standard ASTM-E96/ diffusion through a perforation (Chung et al., 2003), while the film À2 À1 E96-05 (ASTM, 2005) water vapour permeance PR (kg m s ) is itself is considered impermeable (barrier film) (Chung et al., 2003; defined by the equation: Gonzalez et al., 2008). Such modelling approaches are based on Fick’s law of diffusion (Chung et al., 2003) or Stefan–Maxwell law F P PR ¼ ¼ ð2Þ (Rennie and Tavoularis, 2009).