Biodegradable Multilayer Films for Active Food Packaging, Based on Starch and Polyesters with Phenolic Acids

Active biodegradable multilayer films have been developed by thermoprocessing for food packaging purposes, combining improved starch films and a blend of polyesters (PLA-PHBV), with different phenolic acids (ferulic, p-coumaric and protocatechuic).Into the cassava or maize starch films, gums of microbial origin (xanthan and gellan) were incorporated (10%) to improve their functional properties.The gums improved the mechanical and barrier properties to water vapor and oxygen of the starch films.These films were combined with PLA:PHBV blend films in starch-polyester bilayers by thermocompression.The bilayers exhibited high barrier capacity to oxygen and water vapor compared to their respective monolayers.The polyester layer contributes to the mechanical reinforcement of the bilayer, providing high water vapor barrier capacity, while the starch layer provided high oxygen barrier capacity to the bilayer.The bilayer with cassava starch and gellan gum showed the best interlayer adhesion, with adequate functional properties for food packaging applications.Ferulic, p-coumaric and protocatechuic acids, with antimicrobial and antioxidant properties, were incorporated (2%) in the PLA: PHBV blend films to obtain active films.Phenolic acids positively modified the properties of the polyester blend, increasing its elastic modulus and resistance to break and its barrier capacity to water vapor and oxygen, while slightly increasing the Tg of the material.Protocatechuic acid caused the greatest effects, affecting the crystallization of PHBV.The release of these compounds in different food simulants (with high and intermediate polarity) was very limited in terms of release rate and released amount, which reduced the ability of the films to significantly inhibit the growth of Listeria innocua inoculated in culture medium.These films, with and without active compounds, disintegrated under composting conditions, without significant effect of phenolic acids.Films without active compounds and with ferulic acid biodegraded completely after 20 days of composting, whereas films containing p-coumaric and protocatechuic acids did so in 21 and 26 days, respectively.Therefore, none of the incorporated phenolic acids inhibited the biodegradation process, but the process was delayed, depending on the degree of retention of the compound in the polymeric matrix.The biodegradable bilayer films with a layer of starch-gellan and another of PLA: PHBV, with and without phenolic acids, were characterized as to their mechanical properties and barrier capacity to water vapor and oxygen and were used for packaging of pork meat whose quality development was analysed throughout storage time at 5 °C.The presence of phenolic acids decreased the elastic modulus and resistance to break of the bilayers and improved their barrier capacity to water vapor and oxygen.The latter, together with the active effect of the acids, contributed to improving the preservation of the meat during storage, reducing the levels of lipid oxidation, changes in pH and weight losses of the packed samples, as well as microbial growth, especially total coliforms and lactic acid bacteria.Biodegradable bilayer films with phenolic acids, based on starch and polyesters, appeared as a suitable strategy to obtain active packaging materials, with functional properties close to those of some synthetic plastics commonly used in food packaging.These materials can extend the shelf-life of foods, mitigating the environmental impact of plastic packaging since they can be composted.did not significantly inhibit the growth of Listeria innocua due to the limited release of active compounds.Chapter 3, entitled "Biodegradation of PLA-PHBV blend films as affected by the incorporation of different phenolic acids", evaluated the effect of incorporating ferulic, p-coumaric and protocatechuic acids, with antimicrobial activity, into PEG plasticized PLA/PHBV (75:25) blend films, on their disintegration and biodegradation behaviour under laboratory composting conditions.The sample mass loss, thermogradation behaviour and visual appearance were analysed at different times of the composting period.No effect of phenolic acids was observed on the film disintegration pattern, the films being completely disintegrated at the end of composting period.The PLA:PHBV sample without active compounds and with ferulic acid showed complete biodegradation after 20 composting days while the samples with p-coumaric and protocatechuic acids biodegraded 21 and 26 days, respectively.Chapter 4, entitled "Starch-polyester bilayer films with phenolic acids for pork meat preservation", analysed the physical properties of starch-polyester bilayer films incorporating ferulic, p-coumaric and protocatechuic acids, as well as the effect of this active bilayer films at extending the shelf life of pork meat during cold storage.The incorporation of phenolic acids significantly improved the water vapour and oxygen permeabilities and the antioxidant capacity of the active bilayer films, reducing lipid oxidation and decreasing the microbial counts in packaged pork meat during storage.The most relevant results obtained in the different chapters are analysed from a global perspective, in the GENERAL DISCUSSION section.Finally, in the last section the final CONCLUSIONS of the Thesis are presented.