BHT-impregnated film has shown that retards lipid oxidation of
a packaged oatmeal cereal through its migration from the product
via an evaporation/sorption mechanism (Lee et al., 2004). BHT is a
small molecule that exhibits high mobility and therefore has a tendency
to migrate rapidly from packaging materials into foods
(Wessling et al., 1998). Slow release of BHT from the package will
help extend the shelf-life of the food product. The use of antioxidant
packaging has also been proposed to reduce lipid oxidation
in milk (Granda-Restrepo et al., 2009).
Polyurethanes (PUs) are versatile polymers prepared from condensation
of polyisocyanates and polyols. The properties of these
raw materials and their ratio, expressed as NCO/OH, determine
the final properties. PU based materials were not used for contact
in foods probably due to migration of different components and
additives used during their manufacturing. However, several polymeric
materials were tested by Gramiccioni et al. (1986) using
olive oil and isooctane as a liquid simulant for fatty foods and they
found that the global migration values obtained with olive oil and
isooctane for polyurethane were much lower than those for the
PVC based materials. This situation is currently changing as a consequence
of gained knowledge on PU synthesis and the availability
of new raw materials. General properties of polyurethanes can be
modified without using plasticizers or additives just selecting the
raw materials, reducing in this way the global migration and
allowing them to be used in contact with food. The urethane moiety
is a suitable functional group to promote interactions with
other molecules and in particular with active principles capable
of forming hydrogen bonds, modifying in this way their releasing
behavior. On the other hand, polyolefin polymers like polyethylene,
used frequently in food industry, do not have this possibility.