ABSTRACT
Plastics have revolutionized the packaging and transportation of foods, allowing foods to be packaged in light weight materials while offering excellent physical protection against mechanical damage, water vapour transmission and light oxidation. Approximately 70 to 80% of food and ingredients are packaged in polymeric materials (1). However, the use of plastic organic polymers containing functional additives such as plasticizing agents, antioxidants, U.V. light and heat stabilizers or lubricants in the manufacture, packaging and serving of common foodstuffs such as meat, cheese, margarine, bacon, vegetables and beverages may result in these polymer constituents potentially becoming indirect food additives (1, 2). This
phenomenon occurs due to the potential for contact and migration or transfer of polymer components from containers or packaging films into foods during processing, packaging and storage. Plastics (e.g. polyethylene, polypropylene, polystyrene etc.) are also extremely prevalent as food service utensils and containers both inside and outside the home (3, 4). Polymer additives can fall into two functional categories: those that modify the physical properties of polymers, namely catalysts, plasticizers, lubricants and colouring agents etc. and those that have a stabilizing or protective effect on polymer degradation (antiaging additives), such as antioxidants, U.V. light and heat protection agents (5, 6). Plasticizers are synthetic organic additives characterized by low molecular weight with low melting points or low volatility with high boiling
matrix (e.g. phthalic acid esters (PAEs)). They are used to improve the plasticity (e.g. flow, workability and flexibility) of polymers such as the vinyl derivatives (e.g. polyvinyl chloride (PVC), polyvinyl acetate (PVA), polyvinyl alcohol (PVAL)) and the polyolefins (e.g. polyethylene (PE), polypropylene (PP)). In this way, plastic formulations can contain up to 60% of plasticizer materials to transform an otherwise rigid polymer into a plastic with improved physical and mechanical properties such as flexibility, durability, and impact resistance (1, 2, 7). However, due to the relatively low molecular weight of residual polymeric monomers and certain additives (i.e. plasticizers and antioxidants), the migration to and absorption of these compounds by both solid and liquid foods is known to occur (8-10). This may result in off-odours or -flavours being imparted to the packaged food (11, 12) resulting in the loss of product and sales. As well, the toxicology of these substances has been the subject of intense investigation in animal models (13-17) and human subjects (18-21). These issues gain relevance due to the prevalence of microwavable convenience foods which are heated in the packaging containers, as well as the increasing interest in irradiating packaged foods for increased microbiological safety against foodborne illnesses (22-24). Gamma-irradiation of packaged foods is known to result in alterations such as crosslinking and scission of polymeric materials and component additives which may be, in turn, adsorbed by the packaged food contained therein. This chapter will discuss these issues as well as examining potential alternatives to the traditional polymeric packaging materials discussed in the recent literature.
