Membranes for Food Packaging

The development of new materials for food packaging is a challenge that involves scientific and technological competences. Consumer needs and socioeconomic problems are the most important driving forces of this process that has, as ultimate goal, the delivery of high-quality and safe food products to the consumer in an efficient manner [1]. All the materials used as food contact materials (FCM) must have specific and distinctive characteristics. The preliminary requirement is the safety of material. This means that the possible migration of undesirable packaging constituents into the food has to be well known and controlled. The matters of inertness of FCM and packaging reliability are in the domain of law in all the developed countries, where nowadays exist very huge detailed and generally severe regulations on this topic. Other complementary and essential performances concern all those physical and chemical properties that give specific behavior to the material under conditions of use. For example, physical properties such as gas permeation through package walls, mechanical resistance to environmental stress, sealability, and so on, are very important and useful both for controlling the package-fabrication process and to design the food package able to maintain and guarantee the quality and safety of the product during its shelf life. In fact, environmental factors such as humidity, oxygen, light, and so on (which can induce degradation reactions during storage) should be strictly controlled and in some cases modulated by the packaging material. Synthetic polymers are the materials of choice for many food-packaging applications. They have molecular weights typically between 50 000 and 200 000, an optimum range suitable for shaping the polymers into bags, containers, or other forms that give the adequate protection to food during distribution and storage. The typical properties of common plastic packaging materials are reported in Table 10.1. It is important to highlight that the required packaging protection depends on the product characteristics but not always does the proper protection mean the complete isolation of food from the environment-degradation factors. For example, some fatty foods with long shelf life are sensitive to oxygen and light and, as a consequence, the ideal preservation requires the absence of oxygen inside the package, so a high barrier material to reduce the oxygen entrance and, possibly, no light transmission through the package have to be used. On the contrary, for minimally processed vegetables, the natural interplay between the respiration of the product and the transfer of gases through the packaging can lead to an appropriate atmosphere within packages that contributes to maintaining the product freshness during commercialization. In this specific case, the protection by the packaging is granted by films with proper gas permeability that allow the right exchanges between the internal and external sides of the package and not by high barrier materials. In recent years, besides the traditional basic functions of packaging (i.e. protection, communication, convenience, and containment) extra enhanced functions have been sought by the food-packaging sector to meet the consumer demands for minimally processed foods with fewer preservatives, increased regulatory requirements, market globalization, and concern for food safety. Active packaging is the main area in which most of recent innovative ideas have been applied to satisfy these needs, broadening and redefining the function of food packaging. Active packaging has been defined as a system in which the product, the package, and the environment interact in a positive way to extend shelf life or to achieve some characteristics that cannot be obtained otherwise. In other words, active packaging is a new generation of packaging materials that can release active compounds (antimicrobial, antioxidants, enzymes, flavors, nutraceuticals, etc.) or absorb undesirable substances (oxygen, ethylene, moisture, etc.) at controlled rates suitable for enhancing the quality and safety of a wide range of foods during extended storage. In this context, food packaging and membrane developers started collaborations in order to evaluate how membrane science could be applied to food packaging area. In fact, the wide range of properties required to the packaging gives the idea to design and synthesize the membranes as devices that should contribute to maintaining food quality. An example is the fact that recently in the International Membrane Conferences held in Korea (ICOM06, Seoul), in USA (ICOM08, Honolulu) and France (ICOM09, Montpellier) a specific session was devoted to food packaging. Moreover, the USA market for nonseparating membranes used in drug delivery, guided tissue regeneration, batteries, food packaging and high-performance textiles was calculated to be $2.8 billion in 2005, more than half the value of the combined market for all the membranes used in separation and nonseparating applications. The definition of a membrane is not univocal and many attempts have been made to describe it. The most general one may be the following, as reported by Paul and Yampol skii: A membrane is a phase or a group of phase that lies between two different phases, which is physically and/or chemically distinctive from both of them and which, due to its properties and the force field applied is able to control the mass transport between these phases. Membranes, both organic and inorganic, are generally classified based on their morphology as porous, nonporous (dense/tight) and liquid membranes. Depending on the specific membrane properties (porosity, hydrophobicity/hydrophilicity, pore size, etc.), they can be used as packaging materials in modulating the gas exchange rate between the inside and outside of the package environment (modified atmosphere packaging) or in actively controlling the release or absorption of specific compounds to or from the packaged food (active packaging). In this chapter, the use of membranes in food packaging will be analyzed under these two main perspectives, giving results of some examples and potential applications.