Lipid oxidation of a meat product packaged with poly (lactic acid)/clay nanocomposites

Vilarinho, Fernanda; Buonocore, Giovanna; Vaz, M.; Sanches-Silva, A.

http://hdl.handle.net/10400.18/4777

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Introduction: Polylactic acid or polylactide (PLA, Poly) is a biodegradable thermoplastic aliphatic polyester derived from renewable resources, such as corn starch, tapioca roots, chips or starch, or sugarcane. Biopolymer nanocomposites are of great interest to the packaging industry as they can overcome the limitations of biopolymers compared to synthetic polymers. In the last two decades, the nanocomposites have been studied intensively, once the addition of fillers such as organoclays, in particular, montmorillonite (MMT), can improve rheological, thermal and mechanical properties of the biopolymers (Jollands M. et al. 2010). The presence of MMT can lead to materials which generally exhibit great property enhancements, mainly due to its intercalation or exfoliation into the polymer chains. In this work, PLA was incorporated with 5% (w/w) Cloisite Na+ prepared through a two-step process: first extrusion of pellets and secondly melted matter was pressed. The nanocomposite was used to pack a model food (salami) in order to evaluate of the ability of the new packaging to inhibit lipid oxidation. Thiobarbituric Acid Reactive Substances (TBARS) assay was used to evaluate the lipid oxidation stage. This assay allows to measure malondialdehyde (MDA) content, which is formed in the lipid oxidation of polyunsaturated fatty acids. Material and Methods: Packaged salami was homogenized with trichloroacetic acid (10 %) in 0.02 M of orthophosphoric acid and the solution was filtered. The filtered solution was homogenized with thiobarbituric acid aqueous solution (0.02 M) and heated at 100 °C for 40 min. Solutions were cooled down and absorbance was measured at 530 nm. Results were expressed as mg MDA per kg of salami. Results and Discussion: Salami slices were packaged with a control film and with the nanocomposite and analysed at initial time and after 15, 30, 60 and 90 days of contact. Results showed that salami packaged with the nanocomposite presented lower amount of MDA after all contact periods, except after 60 days, where there were no differences between control and nanofilm. Conclusion: Although the results showed that the new nanocomposite tends to reduce the production of MDA, further studies should be carried out to confirm the inhibition of lipid oxidation, such as the peroxide index, p-anisidine value, or the monitorization of a lipid oxidation indicator like hexanal.