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Control the release of natural antioxidants from polymer packaging with cyclodextrins.

Synthetic antioxidants have traditionally been added directly to food products in a single initial dose to protect against the autoxidation of lipids and the generation of free radicals. Natural antioxidants lose their activity and become pro-oxidants at high concentrations. So, there is a need to develop active packaging systems that can gradually deliver antioxidants in a controlled manner.

Researchers at Virginia Tech found that encapsulating antioxidants at the molecular level in cyclodextrins may be a way to create a controlled release mechanism for polymer food packaging systems. Such an approach could gradually deliver an effective antioxidant concentration to a product and limit the oxidation process, while at the same time maintain nutritional quality and extend shelf life.

The scientists attempted to form and characterize cyclodextrin inclusion complexes with the natural antioxidants alpha-tocopherol and quercetin. They also wanted to incorporate cyclodextrin inclusion complexes containing natural antioxidants into linear low-density polyethylene (LLDPE) and measure the release kinetics of the complexes from LLDPE into a model food system.

The scientists formed cyclodextrin inclusion complexes of alpha-tocopherol and quercetin using a coprecipitation technique. Solid inclusion complex products of alpha-tocopherol:beta-cyclodextrin and quercetin:gamma-cyclodextrin had molar ratios of 1.7. This was equivalent to 18.1% alpha-tocopherol on a weight-by-weight basis (w/w) and 13.0% quercetin (w/w).

Using a twin-screw mixer, the investigators compounded free- and cyclodextrin-complexed antioxidant additives into two LLDPE resins. These were compression-molded into films. The release of alpha-tocopherol and quercetin from LLDPE films into coconut oil at 30 C was quantified by high-performance liquid chromatography for four weeks. The total release of alpha-tocopherol after four weeks reached 57% from the free additives and 7% from the complexed additives, averaged across both the LLDPE resins.

Free alpha-tocopherol was released from the polymer in an initial burst, and this was followed by a decreasing release rate. Cyclodextrins decrease the antioxidant mobility within the bulk polymer by forming inclusion complexes. Alpha-tocopherol was complexed with cyclodextrin to target a sustained, linear release rate of the antioxidant for use in an extended shelf life product.

Incorporating cyclodextrin complexes of natural antioxidants into polymer packaging decelerates the release of active antioxidants to provide a continuous replenishment throughout the entire shelf life of the packaged food. The mechanism of alpha-tocopherol release from the bulk LLDPE polymer film was decelerated by the large molecular weight increase during association of alpha-tocopherol and beta-cyclodextrin. The diffusion coefficient of alpha-tocopherol in LLDPE decreased by a factor of about 100 in its inclusion-complexed form with beta-cyclodextrin, compared with free alpha-tocopherol.

Further information. John Koontz, Department of Food Science and Technology, Virginia Tech, 124B Food Science and Technology, Blacksburg, VA 24061; phone: 540-231-6255; fax: 540-231-9293; email:
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Publication:Emerging Food R&D Report
Date:Oct 1, 2008
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