ORIGINAL PAPER Adaptation of the ORAC assay to the common laboratory equipment and subsequent application to antioxidant plastic films K. Bentayeb & P. Vera & C. Rubio & C. Nerin Received: 21 January 2009 / Revised: 13 March 2009 / Accepted: 23 March 2009 / Published online: 9 April 2009 # Springer-Verlag 2009 Abstract The oxygen radical absorbance capacity (ORAC) method has been adapted to the instrumental laboratory and optimized for the determination of the antioxidant capacity of a novel active packaging. As the ORAC assay requires the monitorization of a reaction at controlled temperature by means of the fluorescence signal decrease over time, specific instrumental is usually necessary. In this work, a common liquid chromatographic device has been adapted to perform the ORAC assay, leaving it accessible to any laboratory. Using this adaptation, five different essential oils have been determined resulting in the following antioxidant order: clove (2.66 g Trolox per gram of essential oil), oregano (2.25), cinnamon (1.93), rosemary (1.66), and ginger (1.47). After incorporating the essential oils to the film, its antioxidant capacity has also been checked and related to the concentration of essential oil as well as the thickness of the active film. The results point out that for the same amount of essential oil incorporated measured as grams per square meter, thicker films have more antioxidant capacity than the thinner and more concentrated ones. Furthermore, the antioxidant capacity found in the films was always higher than expected taking into account the amount of essential oil incorporated. Some likely explanations have been proposed, leading to the improvement of the antioxidant film under development. Keywords ORAC . Antioxidant film . Essential oil . Active packaging Introduction The active packaging and among them the antioxidant ones are becoming more and more important, as it is a good way to preserve the food against the oxidation process which limits the shelf life of the packaged food. However, when a new material is obtained, its characteristics have to be measured in an objective manner, so that the new material can be referred to a standard or compared with others. It could be argued that knowing the performance of the antioxidant agents used to prepare the active packaging should be enough to demonstrate the antioxidant behavior of the expected material. But this is not true, as, once in the material, the behavior of the active agents does not always correspond exactly to the prediction made. Previous research carried out in this area drove us to develop a new system to measure the antioxidant capacity of the new plastic films containing essential oils as antioxidant agents [1, 2]. This system was based in the hydroxylation of salicylic acid by the OH radicals and the decrease of the hydroxylated products in the presence of the new antioxidant plastic was quantitatively measured. Thus, the mechanism of action as radical scavenger of the new active plastic was demonstrated. Nonetheless, the test requires more than 10 h is not very practical for daily control in industry. On the other hand, the developed system is mainly based on hydroxyl radicals and the radical scavenger in fact acts on all kind of radicals. Futhermore, the antioxidant capacity of the product depends not only on the film but also on the packaging shape, the free volume, the atmosphere inside the packaging during the product shelf life, and, of course, on the natural features of the food. This fact involves the optimization of the antioxidant tailor-made packaging. When developing a new antioxidant active packaging material, it is important to be able to evaluate its final Anal Bioanal Chem (2009) 394:903–910 DOI 10.1007/s00216-009-2766-0 K. Bentayeb : P. Vera : C. Rubio : C. Nerin (*) Department of Analytical Chemistry i3A, CPS, University of Zaragoza, María de Luna 3, 50018 Zaragossa, Spain e-mail: cnerin@unizar.es