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PEER-REVIEWED REVIEW ARTICLE
Although more seldomly measured compared to oxygen/air, water, and water vapor permeability, the fat/oil/grease barrier performance is very important in the food packaging industry (Lavoine et al. 2012). This is due to an inherently high fat content in many food products (Leminen et al. 2015). Moreover, a few different methods of measurement for grease and oil exist. According to Auvinen and Lahtinen (2008), the amount of grease or oil penetration into a film material depends on both internal and external factors. The internal factors govern properties such as the relation of saturated fats to unsaturated fats and the average length of fat chains; the external factors govern the temperature and the relative humidity. Several options for the measurement of oil absorption are available: the COBB-Ungern method (SCAN-P 37:77 1976), the Kit-test (TAPPI Test Method T 559 cm-12 2012), and the ASTM F119-82 (2015) standard test are some of the most commonly applied methods. Other types of phenomena that need to be minimized in order to protect the package content are worth mentioning. In fact, the barrier film itself is not necessarily inert to the package ’s contents. Instead, it may release molecular species to the contained product. These can include volatile organic compounds (VOCs), including aromatic compounds, flavors, and fragrances. In EC No 10/2011 of the European Union (EU) legislation for plastic materials, the unit of migration is mg/kg. Here, migration loosely refers to mass transport through the barrier film, which affects food safety and quality, and involves direct contact with the package content and the package layer (Auvinen and Lahtinen 2008). In addition, pathogens, including various microbes and bacteria, such as Escherichia coli and Staphylococcus aureus , can harm the package content. Finally, given frequencies of light radiation can deteriorate the package content. UV light can cause harm to the package content by inducing oxidative rancidity. Likewise, fat- containing products tend to deteriorate when exposed to sunlight. In commercial packaging materials, a coating of aluminum foil is often used for protection against UV light (Paine and Paine1992; Kirwan 2005; Lavoine et al. 2012). WOOD BASED BARRIERS Wood consists mainly of cellulose (40% to 50%), hemicellulose (25% to 35%), and lignin (18% to 35%) (Pettersen 1984). These materials can be also isolated from various agro-based feedstocks (Laine et al. 2013) and, in fact, cellulose, hemicellulose, and lignin are the most abundant plant-based natural polymers (Klemm et al. 2005; Antonsson et al. 2008; Albertsson et al. 2011). Interesting properties from the barrier point of view have been discussed in several studies. In this section cellulose derivatives, nanocellulose, lignin, and hemicellulose are considered. Cellulose Derivatives Before adoption of petroleum-derived plastics, several commercially-produced cellulose plastics (cellulosics, cellulose chemicals, or cellulose derivatives) have been commonly used. From 1960s onwards, the superior performance and low cost of petroleum-derived plastics made them more attractive. Many large volume cellulose derivatives are still used today, in specific applications (Gilbert 2017). Cellulose derivatives are prepared from native cellulose, which is hydrophilic, yet water insoluble. Common cellulose derivatives are soluble in various industrial solvents, and this can be a great advantage for processing and for film development (Rastogi and Samyn 2015). The
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Helanto et al. (2019). “ Bio-based barriers ,” B io R esources 14(2), Pg #s to be added.
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