Most oxygen scavenging systems are based on the oxidation of iron and depend on the incorporation of an oxygen-scavenging component into the package, rather than an active packaging material. Ferrous iron powder is often used as the active agent. It is typically contained in a small high oxygen-permeable sachet to separate it from the food product (see Fig. 4.1). A disadvantage of systems of this type is that the water activity of the product must be high enough for the moisture to trigger the scavenging reaction. The sachet also pose a real risk to consumers as large amounts of iron could be accidentally ingested and there is the danger that it could leak, causing contamination or undesirable changes in the odour and flavour of the packaged product. It is clear that active packaging solutions that do not depend on sachets would be an improvement. There have been attempts to disperse ferrous iron compounds directly into polymer matrices; however, this causes their effectiveness to diminish as the active compound is poorly dispersed or quickly deactivated. The development of new active oxygen scavenging packaging materials with higher levels of efficacy would be of benefit to the food industry. Some oxygen scavenging films have been developed by adding titanium dioxide (TiO2) nanoparticles to different polymers, but since TiO2 acts by a photocatalytic mechanism, its major drawback is the requirement of UV light for activation. Aerobic microorganisms have also been used as oxygen-scavenging ‘active compounds’ in hydroxyethyl cellulose and PVOH active coatings for high humidity foods, but their efficiency is restricted by the hydration conditions and the matrices in which they are entrapped.